Download doc midterm 1 chapter notes

A little key (you’ll find I’m freakishly organized):
Bold terms: correspond to bold terms in the book, for which there are definitions.
Italic terms: Names of researchers (I don’t know if we’ll need to know these, but they’re there anyways)
Chapter 1: Introduction
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In ancient times, movements were thought to be made by animating spirits: animism.
They’ve since abandoned this approach, in favour of physical explanations.
Humans think we have something intangible that animates us; a spirit, a mind, a soul.
Does the mind control the nervous system? Is it a part of the nervous system? This is THE MIND-BODY
QUESTION.
Dualism: The belief that the body is physical but the mind (or soul) is not.
Monism: The belief that the world consists only of matter and energy and that the mind is a phenomenon
produced by the workings of the nervous system.
Scientists believe that we will eventually be able to solve the mind-body problem through empirical, practical and
monistic approaches.
Understanding Human Consciousness: A Physiological Approach
 Consciousness in this sense means that we are aware of our thoughts, perceptions, memories and feelings.
 We can hypothesize that consciousness is a physiological function, just like behaviour.
 It is possible that our ability to communicate gave rise to consciousness.
o Our ability to send and receive messages with other people enables us to send and receive our own
messages inside our own heads.
Blindsight: The ability of a person who cannot see objects in his or her blind field to accurately reach for them while
remaining unconscious of perceiving them; caused by damage to the “mammalian” visual system of the brain. (See Figure
1.2)
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Suggests that the common belief that we must perceive something in order for our behaviour to be affected is
false. We can be guided by something that enters into our sensation, without being aware of it at all.
Two systems of the visual system can explain blindsight:
o First, more primitive system evolved mainly for controlling eye movements and bringing to our attention
sudden movements that occur off to the side of our field of vision.
o Second, “mammalian” visual system, is responsible for our perception of the world around us. Blindsight
is caused by damage to this system.
We use the primitive system during blindsight, so we can reach for objects even though we don’t know what
we’re looking at.
This suggests that consciousness is not a general property of all parts of the brain.
Split Brains
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Surgical procedures disconnect two parts of the brain, to help with severe epilepsy. Nerve cells on one side of the
brain become overactive, and the activitiy is transmitted to the other side of the brain via the corpus callosum:
The largest commissure of the brain, interconnecting the areas of neocortex on each side of the brain. These
transmissions cause seizures.
Split-brain operation: Brain surgery that is occasionally performed to treat a form of epilepsy; the surgeon cuts
the corpus callosum. This can greatly reduce the frequency of epileptic seizures.
Cerebral hemispheres: The two symmetrical halves of the brain; constitute the major part of the brain. The
corpus callosum allows communication between the two halves.
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Example: the right hemisphere of an epileptic person with a split brain is capable of understanding instructions,
but is totally incapable of producing speech.
A person will find themselves putting down a book held in their left hand even though they’re very interested,
because the right hemisphere (which controls movement of the left hand) cannot read, and therefore finds the
book boring.
Unilateral Neglect: A syndrome in which people ignored objects located toward their left and the left sides of objects
located anywhere; most often caused by damage to the right parietal lobe.
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The parietal cortex is responsible for putting together information about the movements and location of the parts
of the body with the locations of objects in space around us.
The can sense things on the left side of their bodies, but they just act as if it doesn’t exist.
Volpe, LeDoux, Gazzaniga: presented subjects with a stimulus on the left and right visual fields. The subjects
reported seeing only the one in the right visual field, but when asked if the two stimuli were identical, the
answered correctly.
People with unilateral neglect fail to notice not only things to their left, but also the left halves of things.
This also comes out when they draw pictures (Drawing only the right half of a clock, a flower).
Bisiach and Luzzatti: asked patients to imagine themselves standing to the north of a piazza; they described only
the west side (to their right). When they imagine themselves standing to the south, they described only the east
side.
Damage to the left parietal lobe does not produce unilateral neglect as much as damage to the right parietal lobe,
as much as to be considered nonexistent. Why? Nobody knows yet.
Ehrsson, Spence and Passingham: the rubber hand illusion: See figure 1.6. If we hide our left hand and place a
rubber hand, stroking them at the same time, we begin to feel the rubber hand as our own.
MRI revealed activity in the parietal lobe and the prefrontal cortex, involved in planned movements. When the
parietal lobe passes information to the prefrontal cortex, we begin to feel the rubber hand as our own.
Furthermore, if the rubber hand was threatened with a stab, we react, as if the hand were our own.
The Nature of Physiological Psychology
 The primary function of the brain is control of movement, which is supported by our memory, perception, reason,
etc.
The Goals of Research
 Scientific explanation takes two forms:
1. Generalization: a general conclusion based on many observations of similar phenomena.
o General laws predict specific behaviours. Example, a fear of dogs can be explained by classical
conditioning.
2. Reduction: A phenomenon is described in terms of the more elementary processes that underlie it.
o Example: describing the movement of a muscle as the movements of membranes of muscle cells, or
chemicals entering and exiting the cells.
 It is not enough to simply use reduction, because the same behaviour may be caused by a number of different
physiological phenomena.
 In reality, physiological psychologists use both generalization and reduction as forms of explanation.
Biological Roots of Physiological Psychology
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Has its roots in antiquity (Egyptian, Indian and Chinese Cultures).
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They believed the heart was the seat of thought and emotions, because it beat harder when we were feeling
emotions.
Hippocrates concluded that the role should be assigned to the brain.
o Aristotle disagreed, saying the brain acted to calm the passions of the heart.
o Galen discounted this, saying that if it were so, then nerve endings would go to the heart, not the mind.
René Descartes, said that animals (including humans) are machines, and once set on this earth behave without any
divine intervention.
He defined the term reflex: An automatic, stereotyped movement that is produced as a direct result of a stimulus.
He said that energy coming from an outside source would be reflected back through the nervous system to the
muscles, which would contract (we of course have a different explanation for this now.)
Descartes was a dualist, but he was the first to hypothesize a link between the brain and the mind:
o The mind controls movement, while the body provided information to the mind, via the brain.
o This interaction was said to take place in the pineal body, a small organ at the top of the brain stem.
o He noted that the brain contained fluid-filled VENTRICLES, and when the mind wanted to move, it tilted
the pineal body like a joystick, causing fluid to flow from the brain to the appropriate set of nerves.
Descartes used a model of moving bronze statues, which work in much the same way, to come to his conclusion.
Model: A mathematical or physical analogy for a physiological process; for example, computers have been used
as models for various functions of the brain.
It did not take long for this model to be tested experimentally, and to prove that Descartes was wrong.
Galvani discovered that electrical impulses toward a nerve cause the muscle to which it is attached to move,
regardless of activity in the brain. Therefore, the ability of a nerve to send a message to the muscles is a
characteristic of the tissue itself.
Johannes Müller:
o A prominent nineteenth-century physiologist, who applied experimental techniques.
o Doctrine of specific nerve energies: Müller’s conclusion that because all nerve fibers carry the same
type of message, sensory information must be specified by the particular nerve fibers that are active.
o Example, we receive optical information from auditory nerves, and auditory information from auditory
nerves.
o Explanation: although the information sent is the same, the different nerves go to different parts of the
brain, and are thus interpreted differently.
Pierre Flourens:
o Removed various parts of animals’ brains and observed their behavior;
o Brain ablation: The research method in which the function of a part of the brain is inferred by observing
the behaviors and animal can no longer perform after that part is damaged.
o Flourens claimed to have discovered regions of the brain that control heart rate and breathing, purposeful
movements, and visual and auditory reflexes.
Paul Broca:
o Applied the brian ablation technique to humans, by observing the behavior of those whose brains had
been damaged by strokes.
o Observations of those who could no longer speak, led him to conclude that there was an area in the left
side of the brain performing functions necessary for speech.
Gustav Fritsch and Eduard Hitzig:
o Applied a current to a dog’s brain and observed the effects.
o Stimulation of specific parts of the brain led to contractions of specific muscles on the opposite side of the
body. This region is now called the PRIMARY MOTOR CORTEX.
Hermann von Helmholtz:
o Provided many great discoveries, including theories of color vision.
o He opposed Muller in that he believed all physiological phenomena can be subject to experimental
investigation (they are all mechanistic).
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He also found that neural conduction was much slower than conduction through an electrical wire (only
about 90 ft per second).
Natural Selection and Evolution (Formulated by Charles Darwin)
Functionalism and the Inheritance of Traits
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Darwin emphasized that all of the characteristics of an organism have functional significance (for example,
camouflage, nest construction).
The brain is inherited by future generations, and this causes similar behaviors to occur.
Functionalism: The principle that the best way to understand a biological phenomenon (a behavior or a
physiological structure) is to try to understand its useful functions for the organism.
Difference between machines and organisms: machines have an inventor, who designed the function of the
machine purposefully. Organisms are the result of a long series of accidents.
Therefore, we cannot say that a specific mechanism in an organism has a PURPOSE. We instead say that it has a
FUNCTION.
The cornerstone of Darwin’s theory of acquiring adaptive characteristics, is that of natural selection: The process
by which inherited traits that confer a selective advantage (increase an animal’s likelihood to live and reproduce)
become more prevalent in a population.
Darwin noted that not all members of a species are identical, and these differences are inherited by their offspring.
If a particular difference (trait) permits the organisms to more successfully reproduce, then they will reproduce
more, sending those traits to their offspring, who in turn will reproduce more themselves. Thus, the trait will
become more prevalent in future generations.
In ARTIFICIAL SELECTION (selective breeding of dogs, for instance), can produce such a variety of different
breeds, then Darwin hypothesized that NATURAL SELECTION could produce speciation.
Here’s how it works:
o Cells contain chromosomes, which are molecules that contain the recipes for producing the proteins that
cells need to grow and to perform their functions.
o These “blueprints” get altered, through a mutation: A change in the genetic information contained in the
chromosomes of sperms or eggs, which can be passed on to an organisms’ offspring; provides genetic
variability.
o Most mutations are not advantageous, they provide a sort of handicap to the offspring. But every so often
the mutations confer a selective advantage: A characteristic of an organism that permits it o produce
more than the average number of offspring of its species.
The effects of the physical alterations can be seen in our behavior.
o Example: if a mutation occurs changing the structure of the brain, which tells an animal to freeze upon
viewing a novel stimulus, this animal will be less likely to be preyed upon, giving it a selective advantage.
Evolution of the Human Species
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Evolution: A gradual change in the structure and physiology of plant and animal species (I don’t know why they
don’t include other types of organisms… But whatever) – generally producing more complex organisms – as a
result of natural selection.
The first vertebrates to emerge from the sea were amphibians.
Seventy million years later, the first reptiles appeared, providing an advantage over amphibians, because they
could lay their eggs out of the water.
Reptiles divided into three lines: the ANAPSIDS (ancestors of today’s turtles), DIAPSIDS (ancestors of dinosaurs,
birds, lizards, crocodiles, snakes), and SYNAPSIDS (ancestors of mammals.)
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One group of synapsids called the THERAPSIDS became the dominant land animal during the Permian period,
the end of which was marked by a mass extinction.
One species of therapsid called CYNODONT survived, and became the ancestor of all mammals.
The earliest mammals had poor eyesight, but good hearing, because of the malleus, incus, and stapes in the ear
(reptiles only had the stapes). They hunted at night when larger predators couldn’t see insects.
Another mass extinction occurred 65 million years ago, due to a meteorite in the Yucatan peninsula. This killed
off all the dinosaurs, allowing mammals to flourish.
Primates evolved; then, as fruit-bearing trees evolved in a proper climate, fruit-eating primates evolved. The early
advantage of color vision was to tell the difference between fruits.
The first HOMINIDS appeared in Africa, in woodlands and the savanna.
The primates evolved characteristics that allowed them to gather roots and tubers, to hunt and kill game, and to
defend themselves. They used tools, produced clothing, constructed dwellings; they discovered fire, they
domesticated dogs, and eventually developed language.
The closest relatives of humans are chimpanzees (with whom we share 98.8% of our DNA), gorillas and
orangutans.
Homo erectus was the first hominid to leave Africa, and scattered across Europe and Asia.
Our own species, homo sapiens, evolved in East Africa around 100,000 years ago.
Evolution of Large Brains
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A large brain requires a large skull, and an upright position limits the size of a woman’s birth canal.
Therefore, the brain starts out small, and continues to grow as the baby grows.
All mammals require extensive parental care, providing them with the tools they need to survive in the world. For
this reason, the brain is capable of being rewired or “programmed”.
The human brain is large IN PROPORTION TO OUR BODY SIZE. In fact, elephants and whales have a much
larger brain than us, but our brain takes up 2.3% of our body weight, while an elephant’s brain takes up 0.2% of
its body weight.
The shrew brain takes up 3.3% of the body weight, but it is far less complex than a human brain, so the
explanation needs more work.
Although bigger bodies require bigger brains, the size of the brain does not have to go up proportionally with that
of the body.
What counts is having a brain with plenty of nerve cells that are not devoted to moving muscles or analyzing
sensory information. These cells are available for learning, remembering, reasoning, and making plans.
What also matters is the number of neurons per gram of tissue. More neurons/gram, the more intelligent the
species.
Evidence for the development of a large brain is the slowing of the process of brain development, allowing more
time for growth. Neoteny: A slowing of the process of maturation, allowing more time for growth; an important
factor in the development of large brains.
Ethical Issues in Research with Animals
 We must make sure when we do animal research that it is both humane and worthwhile.
 Most regions have strict rules for doing surgery, keeping the animals in safe and happy conditions, and the vast
majority of laboratory animals are treated humanely.
 Whether it is worthwhile is difficult to say.
 In fact, pet owners cause more suffering among animals than do researchers. Pet owners are not bound by the
same laws as researchers are.
 Animal rights activists seem to spend more time targeting researchers (who rarely mistreat animals) than they do
targeting animal uses of food, furs, hunting, etc.
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Research is the one indispensable use of animals. We can do without eating animals, hunting, etc. but we cannot
make advances in discovering cures for diseases without the use of animals.
The pursuit of knowledge is also a good endeavour for its own sake, and this also sometimes requires use of
animals.
Careers in Neuroscience
 Physiological Psychologist: A scientist who studies the physiology of behavior, primarily by performing
physiological and behavioral experiments with laboratory animals.
 Study such topics as sensory processes, sleep, emotional behavior, ingestive behavior, aggressive behavior, sexual
behavior, parental behavior, learning and memory.
 Other terms: biological psychology, biopsychology, psychobiology, behavioral neuroscience.
 It belongs to the larger field of neuroscience, concerning itself with all aspects of the nervous system.
 Two other overlapping fields: neurology and experimental neuropsychology (cognitive neuroscience).
Neurologists are physicians that treat diseases of the nervous system.
 Cognitive neuroscientists specialize in studying the behavior of those whose brains have been damaged.
(I won’t put the last section here as there isn’t really any content, but have a look if you want to know how the book is
organized. The section titled “Strategies for Learning”, on p. 26.)
QUESTIONS QUESTIONS QUESTIONS! (Answers on the last page) (BTW, these questions are my creation, so if there
are any problems or things that are blatantly wrong, let me know: [email protected])
1. ______ is the belief that the body is physical but the mind (or soul) is not; ______ is the belief that the world
consists only of matter and energy and that the mind is a phenomenon produced by the workings of the nervous
system.
a. Monism; Dualism
b. Neoteny; Reduction
c. Dualism; Monism
d. Reduction; Neoteny
2. Brain ablation is a technique used by scientists to discover the function of a particular region of the brain, in
which
a. subjects are hooked up to an fMRI scanner and electrical activity is noted when the subject is asked to
perform certain tasks.
b. different parts of the brain are electrically stimulated, and the resulting behavior is noted.
c. researchers open the skull and look at the little squiggly blue electricity lines that travel between the
neurons, while asking them to perform certain tasks.
d. The behavior that can no longer be performed by an animal is observed, after a part of the brain has been
damaged or removed.
3. An animal with more neurons per gram of tissue in the brain will be ______ intelligent as (than) an animal with
less neurons per gram of tissue in the brain.
a. more
b. less
c. equally
d. None of the above
Answers: 1. C; 2. D; 3. A
Chapter 2: Structure and Functions of Cells of the Nervous System
Sensory neuron: Neuron that detects changes in external or internal environment and sends info about these
changes to CNS
Motor neuron: Neuron located within CNS that controls contraction of muscle or secretion of gland
Interneuron: Neuron located entirely within central nervous system (between sensory neurons and motor
neurons)
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Local interneurons form circuits with nearby neurons and analyze small pieces of info
Relay interneurons connect circuits of local interneurons in one region of brain with those in other
regions
Central nervous system (CNS): Brain and spinal cord
Peripheral nervous system (PNS): Part of nervous system outside the brain and spinal cord, including nerves
attached to brain and spinal cord
Soma (Cell body): Cell body of neuron, contains nucleus
Dendrites: Branched structure attached to soma of neuron; receives info from terminal buttons of other neurons
Synapse: Junction between terminal button of axon (sending cell) and somatic (soma) or dendritic membrane of
receiving cell
Axon: Long, thin, cylindrical structure; carries info from cell body to terminal buttons
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Covered by myelin sheath
Basic message it carries: action potential
When action potential reaches point where axon branches, it splits but does NOT diminish in size. Each
branch receives full-strength action potential
Multipolar neuron: Neuron with one axon and many dendrites attached to its soma (FIG 2.1)
Bipolar neuron: Neuron with one axon and one dendrite attached to soma; found in sensory systems (ex.
Vision and audition)
Unipolar neuron: Neuron with one axon attached to its soma; axon divides, one branch receiving sensory info
(dendrites) and other sending info (terminal buttons) into CNS; found in somatosensory system (touch, pain,
sensory events that affect skin) (FIG 2.2)
Terminal buttons: Bud at end of branch of an axon; forms synapses with another neuron; sends info to that
neuron
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When action potential traveling down axon reaches terminal buttons, they secrete neurotransmitter, a
chemical that has an excitatory or inhibitory effect on another neuron
Membrane: Defines the boundary of cell. Consists of double lipid layer. Embedded proteins in membrane:
detect substances outside cell (like hormones) and pass info about presence of these substances to interior of
cell. Other proteins control access to interior of cell (selectively permeable). Some act as transporters, actively
carrying molecules into or out.
Nucleus: Structure in central region of cell, containing nucleolus (produces ribosomes [involved in protein
synthesis, is site of production of proteins translated from mRNA]) and chromosomes (long strands of DNA
[long, complex macromolecule consisting of two interconnected helical strands; contain organism’s genetic
info])
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mRNA: Macromolecule that delivers genetic info concerning synthesis of protein from portion of
chromosome to a ribosome
Gene: functional unit of chromosome, which directs synthesis of one or more proteins
Enzymes: molecule that controls chemical reaction, combining two substances or breaking a substance into two
parts.
Genome is sequence of nucleotide bases on chromosomes that provide info needed to synthesize all proteins
that can be produced by a particular organism
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1.5 percent of human genome encodes from proteins; amount of genome that codes for proteins does
NOT correlate to organism’s complexity
Non-protein-coding DNA does correlate with complexity of organism
Non-coding RNA (ncRNA): Form of RNA that does NOT encode for protein
o Constitutes spliceosomes, a molecule that cuts mRNA into pieces, discard some parts, and splice
(glue) the pieces back together
o Can attach to, and modify, proteins that regulate gene expression
Cytoplasm: Viscous, semiliquid substance contained in interior of cell; contains organelles
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Mitochondria: Organelle responsible for extracting energy from nutrients; inner membrane made up of
wrinkles (cristae)
o Adensodine triphosphate (ATP): Molecule important to cellular energy metabolism; its
breakdown liberates energy
Endoplasmic reticulum: Rough ER contains ribosomes and is involved with productions of secreted proteins.
Smooth ER is site of synthesis of lipids and provides channels for segregation of molecules involved in various
cell processes. ER used for storage and as a channel for transporting chemicals through cytoplasm
Golgi apparatus: Complex molecules (made of simpler individual molecules) are assembled here. Packages
products of secretory cell (like those that release hormones)
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Exocytosis: Secretion of substance by a cell through means of vesicles; the process by which
neurotransmitters are secreted
Golgi also produces lysosomes: Organelle containing enzymes that break down waste products
Cytoskeleton: Gives cells its shape; made of 3 types of protein strands, linked together, forming a cohesive
mass.
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Microtubules: thickest strand; long strand of bundles of protein filaments arranged around a hollow
core; involved in transporting substances from place to place within cell
o Axoplasm: cytoplasm of axon
 Axoplasmic transport: Active process by which substances are propelled along
microtubules that run length of axon (FIG 2.8)
 Anterograde axoplasmic transport: Movement from soma to terminal buttons
o Done by molecules of protein kinesin, which “walks” down microtubule,
carrying cargo to its destination
 Retrograde axoplasmic transport: Movement from terminal buttons to soma;
protein dynein carries substances in this transport
Neuroglia: Important supporting cells of CNS, “nerve glue”
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Glia: Supporting cells of CNS; they surround neurons and hold them in place, controlling their supply
of nutrients and some chemicals they need to exchange messages with other neurons; they insulate
neurons from one another; they can destroy and remove dead or injured neurons.
o Astrocyte: Provides physical support to neurons and clean up debris within brain (phagocytosis,
“eating”); provides nutrients and other substances (provides nourishment to neurons), and
regulates chemical composition of extracellular fluid (FIG 2.9)
 Neurons receive some glucose directly from capillaries BUT they receive MOST of their
nutrients from astrocytes; astrocytes receive glucose from capillaries and break it down to
lactaterelease lactate into extracellular fluidneuron takes it up and transport it to
mitochondria for energy
 Also, they store carbohydrate glycogen which is used when metabolic rate of neurons is
very high
 Once dead tissue broken down, framework of astrocytes will fill vacant area, and form
scar tissue, walling off the area
o Oligodendrocytes: Supports axons and produces myelin sheath, which insulates most axons
from each other (prevents messages from spreading between adjacent axons); surrounds many
axons in CNS
 Node of Ranvier: Naked portion of myelinated axon, between adjacent oligodendroglia
or Schwann cells
o Microglia: smallest of glial cells; like astrocytes, act as phagocytes, engulfing and breaking
down dead and dying neurons. Serve as one of the representatives of immune system in brain,
protecting brain from invading microorganisms. Primarily responsible for inflammatory reaction
in response to brain damage.
Schwann cells: Cell in PNS that is wrapped around a myelinated axon, providing one segment of its myelin
sheath; Schwann cell provides myelin for only one axon
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Help in digestion of dead and dying axons. After, Schwann cells arrange themselves in series of
cylinders that act as guides for regrowth of axons (FIG 2.11)
In CNS, axon damage new sprouts of axon will form (like in PNS) BUT budding axons encounter scar tissue
produced by astrocytes, and they can NOT penetrate this barrier. Even if they did, axons would not re-establish
their original connections without guidance similar to Schwann cells in PNS.
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Development of axons; two modes of growth:
o 1st mode: Elongate to reach target (Schwann cells provides this signal)
o 2nd mode: Stop elongating and begin sprouting terminal buttons
 Even if astrocyte does NOT produce scar tissue, they produce a chemical signal that
instructs regenerating axons to begin 2nd mode; stops before it reaches target
o Difference in regenerative properties of axons in CNS and PNS results from differences in
characteristics of supporting cells, not from differences in axons
o Composition of myelin is different between oligodendrocytes of CNS and Schwann cells of
PNS; (i.e. immune system of multiple sclerosis patients attack oligodendrocytes only)
Blood-Brain barrier: Semipermeable barrier between blood and brain produced by cells in wall of brain’s
capillaries (FIG 2.12)
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Ehrlich; injected blue dye into animal’s bloodstream and all tissues EXCEPT the brain and spinal cord
were blue
o Injected blue into fluid-filled ventricles of brain, and CNS turned blue
Selectively permeable; cells that line capillaries (in body) do not fit together tightly; small gaps are
found between them, permitting free exchange between blood plasma and fluid outside the capillaries
that surrounds cells of body
o In CNS, capillaries lack small gaps (but have extremely small gaps) many substances cannot
leave the blood (blood-brain barrier)needs to be actively transported through capillary walls by
special proteins (ex. Glucose transporters)
Function: Presence of blood-brain barrier helps regulate composition of extracellular fluid that surrounds
neurons. Transmission of messages in brain depends on delicate balance between substances within
neurons and extracellular fluid; if changed slightly, transmission disruptedbrain function disrupted
Area postrema: Region of medulla (p.93) where blood-brain barrier is weak; poisons can be detected there
(poisons in the blood, entering circulator system from stomach) and can initiate vomiting
Neural communication; See FIG 2.13 & 2.14
Electrodes: Conductive medium that can be used to apply electrical stimulation or to record electrical
potentials
Microelectrode: Very fine electrode, generally used to record activity of individual axons (FIG 2.16)
Membrane potential: Electrical charge across a cell membrane; difference in electrical potential inside and
outside the cell
Oscilloscope: Lab instrument that is capable of displaying a graph of voltage as a function of time on the face
of a cathode ray tube
Resting potential: Membrane potential of neuron when it is not being altered by excitatory or inhibitory
postsynaptic potentials; ~ -70mV in giant squid axon
Depolarization: Reduction (toward zero) of membrane potential of a cell from its normal resting potential
(positive charge applied to inside of membrane)
Hyperpolarization: Increase in membrane potential of cell, relative to normal resting potential (more polarized,
negative) FIG 2.17
Action potential: Brief electrical impulse that provides basis for conduction of info along an axon; very rapid
reversal of membrane potential (see p.45)
Threshold of excitation: Value of membrane potential that must be reached to produce an action potential
Diffusion: Movement of molecules from regions of high concentration to regions of low concentration
Electrolytes: Aqueous solution of a material that ionizes (substances that have the property that when dissolved
in water, split into parts with opposing charge) – soluble acid, base, or salt
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Ion: Charged molecule. Cations are positively charged, anions are negatively charged
Electrostatic pressure: Force exerted by attraction (between charged particles of opposite charges) or
repulsion (between charged particles of same charge) (See FIG 2.18)
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Na+ is driven inside the cell by diffusion and electrostatic pressure
Cell membrane is ~100 times more permeable to K+ than to Na+
Intracellular fluid: Fluid contained within cells
Extracellular fluid: Body fluids located outside of cells
Sodium-potassium transporters: Protein in membrane of all cells that pumps sodium ions out and transports
potassium ions into the cell; 3 Na+ out, 2 K+ in
Ion channel: Specialized protein molecule that permits specific ions to enter or leave cells (FIG 2.20)
Movement of ions during the action potential (FIG 2.21)
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2.
3.
4.
5.
6.
Threshold of excitation reached  Na+ channels open, Na+ enters cell by forces of
diffusion and electrostatic pressure; opening of channels triggered by reduction of membrane potential
(depolarization)
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Voltage dependent ion channels: Ion channel that opens or closes according to
value of membrane potential
K+ channels require greater level of depolarization; opens after Na+ channels; K+
begin to leave cell
Action potential reaches its peak, Na+ channels become refractory – channel
becomes blocked and remains closed until membrane reaches resting potential (no more Na+ enters cell)
K+ continues to leave cell; driven out by diffusion and by electrostatic pressure.
Outflow of cations cause membrane to return to resting level (decreases in +ive charge)
Membrane potential returns to resting state, K+ channels close, Na+ channels reset
(next depolarization can cause them to open again)
Membrane overshoots resting value (-70mV) and gradually returns to normal.
*Accumulation of K+ ions outside the membrane are responsible for this temporary hyperpolarization.
Extra K+ outside diffuse away, and membrane potential returns to -70mV. Sodium-potassium
transporters remove Na+ and retrieve K+
Sodium-potassium transporters are important on a long term basis; without them, concentration of Na+ in
axoplasm would eventually increase enough that the axon no longer functions
All-or-none law: Action potential either occurs or does not occur; once triggered, it is transmitted down axon to
its end; action potential always remains the same size, without growing or diminishing. When action potential
reaches a point where axon branches, it splits but does not diminish in size.
Rate law: Variations in intensity of stimulus or other information being transmitted in an axon are represented
by variations in the rate at which that axon fires (FIG 2.24)
Cable properties: Passive conduction of electrical current, in a decremental fashion, down the length of an
axon

Decremental condution: signal decreases in size (decrements); conduction of weak
depolarization by axon follows cable properties (happens in myelinated axons)
Saltatory conduction: Conduction of action potentials by myelinated axons. Acction potential appears to jump
from one node of Ranvier to the next (FIG 2.26)


Advantage: Economic; Na+ enter myelinated axons only at nods of Ranvier, much
less gets in, and consequently, much less has to be pumped out (an active process, requires ATP)
Advantage: Speed; Conduction of action potential is faster in myelinated axon
because transmission between nodes (by means of axon’s cable properties) is very fast. Increased speed
enables animal to react faster and think faster.
o
Increase size of axon (diameter), increase speed of conduction
Synaptic transmission: Transmission of messages from one neuron to another through synapse; messages
carried by neurotransmitters, released at terminal buttons
Postsynaptic potentials: Alterations in membrane potential of postsynaptic neuron, produced by liberation of
neurotransmitter at synapse (brief depolarizations or hyperpolarizations that increase or decrease rate of firing
of axon in postsynaptic neuron)
Binding site: Location on receptor protein to which ligand binds
Ligand: Chemical that binds with binding site of receptor
Synapses can occur in 3 places: on dendrites, on soma, and on other axons; axodendritic, axosomatic, axoaxonic
(FIG 2.27)

Axodendritic synapses can occur on smooth surface of a dendrite or on dendritic
spines: small protrusion that forms synapses with a terminal button
Presynaptic membrane: Membrane of a terminal button that lies adjacent to postsynaptic membrane and
through which neurotransmitter is released
Postsynaptic membrane: Cell membrane located on the neuron that receives the message (opposite from the
terminal button in a synapse)
Synaptic cleft: Space between presynaptic membrane and postsynaptic membrane
Synaptic vesicles: Small, hollow, beadlike structure found in terminal buttons; contains molecules of a
neurotransmitter


Small synaptic vesicles: Found in all terminal buttons, contain molecules of neurotransmitter
Transport proteins fill vesicles with neurotransmitter, and trafficking proteins are involved in the release
of neurotransmitter and recycling of vesicles
Release zone: Region of interior of presynaptic membrane of synapse to which synaptic vesicles attach and
release their neurotransmitter into synaptic cleft


Large, dense-core synaptic vesicles can be found scattered in the terminal buttons. These vesicles
contain one of a number of different peptides (functions will be described later in this chapter)
FIG 2.28
Postsynaptic density is caused by the presence of receptors – specialized protein molecules that detect presence
of neurotransmitters in synaptic cleft – and protein filaments that hold receptors in place
Release of neurotransmitter *FIG 2.31








Ca2+ are located in highest concentration in extracellular fluid; when voltage-dependent calcium
channels open, Ca2+ flows into cell, propelled by electrostatic pressure and force of diffusion
Entry of Ca2+ is essential; if no Ca2+, an action potential no longer causes the release of
neurotransmitter
Calcium transporter remove intracellular Ca2+, like sodium-potassium transporters removed Na+
Entry of calcium opens fusion pore “omega” figures  release of neurotransmitter
Fusion pore – hole through both membranes that enables them to fuse together (FIG 2.31)
Kiss and stay: Fusion pore of synaptic vesicles open enough for some neurotransmitters to diffuse into
synaptic cleft. Fusion pore closes again, and vesicle remains in docked position. Vesicles are refilled
(Don’t know how)
Kiss and leave: Synaptic vesicles release most or all of their neurotransmitter, the fusion pore closes ,
and then vesicle detaches from presynaptic membrane and joins the pool of Undocked vesicles, where it
gets filled with neurotransmitter again
Synaptic vesicles that merge and recycle merges with presynaptic membrane, making terminal button
slightly larger little buds of membrane pinch off into cytoplasm and merge with other little buds of
membrane, forming pools of membrane (endosomes). Endosomes become synaptic vesicles
o *FIG 2.33
Postsynaptic receptors: Receptor molecule in postsynaptic membrane of synapse that contains binding site for
a neurotransmitter
Neurotransmitter-dependent ion channel: An ion channel that opens when a molecule of neurotransmitter
binds with a postsynaptic receptor
Ionotropic receptor (direct): Receptor that contains a binding site for a neurotransmitter and an ion channel
that opens when a neurotransmitter attaches to binding site
 Ionotropic receptors are sensitive to neurotransmitter acetylcholine and contain sodium channels
Metabotropic receptor (indirect): Receptor that contains a binding site for a neurotransmitter; activates an
enzyme that begins a series of events that opens an ion channel elsewhere in membrane of cell when a molecule
of neurotransmitter attaches to binding site (FIG 2.35)
 G protein: Protein coupled to metabotropic receptor; conveys messages to other molecules when a
ligand binds with and activates the receptor
 Second messenger: Chemical produced when G protein activates an enzyme; carries a signal that
results in the opening of ion channel or causes other events to occur in the cell (FIG 2.35 b)
 Potentials produced by metabotropic receptors take longer to begin and last longer
o First second messenger discovered: cyclic AMP, chemical that is synthesized from ATP
 Second messengers important in both synaptic and nonsynaptic communication.
o They can travel to nucleus or other regions of neuron and initiate biochemical changes that affect
the functions of the cells. Can turn specific genes on or off initiating/terminating production
of particular proteins
Excitatory postsynaptic potential (EPSP): Excitatory depolarization of postsynaptic membrane of a synapse
caused by liberation of a neurotransmitter by terminal button *FIG 2.36 a
Inhibitory postsynaptic potentials (IPSP): Inhibitory hyperpolarization of postsynaptic membrane of a
synapse caused by the liberation of a neurotransmitter by terminal button *FIG 2.36 b
For Cl- at resting potential, nothing happens, forces of diffusion and electrostatic pressure are balanced. If
membrane potential has already been depolarized by activity of excitatory synapses located nearby, Clchannels open, permitting Cl- to enter cell. Influx of anions will bring membrane potential back to normal
resting condition; open Cl- channels serve to neutralize EPSP (FIG 2.36c)
Open Ca2+ channels depolarize the membrane, producing EPSP. Entry of Ca2+ into terminal button triggers
migration of synaptic vesicles and release of neurotransmitter. In dendrites of postsynaptic cell, calcium binds
with and activates special enzymes, which can have a variety of effects (ex. Production of biochemical and
structural changes in postsynaptic neuron)
Reuptake: Reentry of neurotransmitter just liberated by terminal button back through its membrane, thus
terminating the postsynaptic potential (FIG 2.37)
Enzymatic deactivation: Destruction of a neurotransmitter by an enzyme after its release – ex. Destruction of
acetylcholine by acetylcholinesterase
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Acetylcholine (ACh): Neurotransmitter found in brain, spinal cord, and parts of PNS; responsible for
muscle contraction
Acetylcholinesterase (AChE): The enzyme that destroys acetylcholine soon after it is liberated by
terminal buttons, thus terminating the postsynaptic potential. Breaks down ACh into parts: choline and
acetate; neither of this parts are capable of activating postsynaptic receptors postsynaptic potential
terminated
Physostigmine deactivates AChE; cure for curare poisoning b/c increases and prolongs effects of ACh
on postsynaptic membrane, increasing strength of synaptic transmission at synapses
“The rate at which an axon fires is determined by the relative activity of excitatory and inhibitory synapses on
the soma and dendrites of that cell”
Neural integration: Process by which inhibitory and excitatory postsynaptic potentials summate and control
the rate of firing of a neuron
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Axon hillock: located at base of axon *FIG 2.38
Neural inhibition (that is, an inhibitory postsynaptic potential) does NOT always produce behavioural
inhibition. “Inhibition of inhibitory neurons makes behaviour more likely to occur”
The reverse is true: “Excitation of neurons that inhibit a behaviour suppresses that behaviour.” (ex.
Dreaming; set of inhibitory neurons in brain becomes active and prevents us from getting up and acting
out our dreams)
Autoreceptor: Receptor molecule located on a neuron that responds to neurotransmitter released by that neuron.
They regulate internal processes, including synthesis and release of neurotransmitter; they are metabotropic; the
control they exert on these processes is accomplished through G proteins and second messengers

Most times, effects of autoreceptors activation are inhibitory; if too much neurotransmitter is released,
autoreceptors inhibit both production and release; Opposite effect if not enough are released
Axoaxonic synapses do not contribute directly to neural integration. They alter amount of neurotransmitter
released by the terminal buttons of postsynaptic axon. Can produce presynaptic modulation: presynaptic
inhibition or presynaptic facilitation *FIG 2.39
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Presynaptic inhibition: Action of presynaptic terminal button in an axoaxonic synapse; reduces the
amount of neurotransmitter released by the postsynaptic terminal button
Presynaptic facilitation: Action of presynaptic terminal button in an axoaxonic synapse; increase the
amount of neurotransmitter released by postsynaptic terminal button
Small neurons have extremely short processes and lack axons; these neurons form dendrodendritic synapses, or
synapses between dendrites. They do NOT transmit info from place to place within the brain (believed to
perform regulatory functions, perhaps help organize activity of groups of neurons)
Larger neurons also form dendrodendritic synapses. Some of these synapses are chemical. Others are electrical;
the membranes meet and almost touch, forming a gap junction: Special junction between cells that permits
direct communication by means of electrical coupling
Neuromodulators: Naturally secreted substance that acts like a neurotransmitter except that it is not restricted
to synaptic cleft but diffuses through extracellular fluid.
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
Most are peptides, chains of amino acids joined together by peptide bonds. Most neuromodulators, and
some hormones, consists of peptide molecules
Affect general behavioural states such as vigilance, fearfulness and sensitivity to pain
Hormone: Chemical substance that is released by an endocrine gland that has effects on target cells in other
organs. Hormones affect the activity of cells (including neurons) that contain specialized receptors located
either on surface of membrane or deep within their nuclei
Endocrine gland: Gland that liberates its secretions into extracellular fluid around capillaries and hence, into
the bloodstream
Target cells: Type of cell that is directly affected by hormone or other chemical signal; has receptors for
particular hormone

Peptide hormones exert their effects on target cells by stimulating metabotropic receptors
Steroid: Chemical of low molecular weight, derived from cholesterol. Steroid hormones affect their target cells
by attaching to receptors found within nucleus. Soluble in lipids  pass easily through cell membrane (FIG
2.41)
QUESTIONS:
In the ____ form of neurotransmitter release, the terminal button becomes slightly ____ and pieces of
______ become new synaptic vesicles.
Kiss and leave; larger; spliceosomes
Kiss and stay; smaller; endosomes
Kiss and recycle; smaller; G proteins
Merge and recycle; larger; endosomes
Saltatory conduction is advantageous because
Nodes of Ranvier are bypassed.
Less energy is required to operate the sodium-potassium transporters.
It is unaffected by diseases that damage myelin.
It permits myelinated axons to transmit action potentials almost as fast as unmyelinated axons.
Large synaptic vesicles are produced in the _______ and are transported to the _________.
Synapse; extracellular fluid
Cytoplasm; dendrites
Soma; terminal buttons
Dendrites; release zone
Answers:
Merge and recycle; larger; endosomes
Less energy is required to operate the sodium-potassium transporters.
Soma; terminal buttons
Neuro – Chapter 3 – Structure of the nervous system
Note from Julia: This chapter has A LOT of terms. Things get pretty detailed with the structures and I would really
recommend that if you didn’t read the chapter, to look at the pictures in the book. The most important parts are the
definitions (highlighted words), and any extra details I think could be important or would help with your understanding
are in these notes.
Notes:
Ryan B – seizures, ha d seizure surgery where they remove the part of the brain that is causing the problem without
removing parts of the brain that have important functions. Focal-seizure disorder.
Basic Features of the nervous system
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Names of structures in the brain correspond to commonplace objects which may help us remember their function.
Neuraxis: An imaginary line drawn through the center of the length of the central nervous system, from the
bottom of the spinal chord to the front of the forebrain.
o Directions described relative to this structure
Anterior: Located near or toward the head
Posterior: Located near or toward the tail, or the end.
Rostral: In the direction of the front of the face.  beak
Caudal: In the direction away from front of the face.  tail
Dorsal: In the direction perpendicular to the neuraxis toward the top of the head or the back  back or top of
head
Ventral: In the direction perpendicular to the neuraxis toward the bottom of the skull or the front surface of the
body  belly
Lateral: Toward the side of the body, away from middle
Medial: Toward the middle of the body, away from the side.
Ipsilateral: Located on the same side of the body
o i.e olfactory bulb sends signals to ipsilateral hemisphere, or same hemisphere.
Contralateral: Located on the opposite side of the body.
o i.e left cerebral cortex controls contralateral hand, or right hand
There are different ways to slice the brain to see what is there
o Cross Section – A slice taken at right angles to the neuraxis.
 Aka Frontal Sections – A slice through the brain parallel to the forehead.
 **Cross sections of spinal chord would be parallel to the ground.
o Horizontal Sections – A slice through the brain parallel to the ground/
o Sagittal sections – A slice through the brain parallel to the neuraxis and perpendicular to the ground.
 Midsagittal plane – the plane through the neuraxis perpendicular to the ground; divides the brain
into two symmetrical halves.
An overview of the nervous system
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CNS – brain and spinal chord, encased in bone (brain covered by skull, spinal chord covered by vertebral column).
PNS – cranial nerves, spinal nerves, and peripheral ganglia
Brain –
o large mass of neurons, glia, and other supporting cells.
o Most protected organ
o Receives lots of blood and is chemically guarded by barrier
o Received 20% of blood flow consistently
o
 Needs it because it can’t store its own fuel
6 second interruption would produce unconsciousness and a few minutes would create damage.
Meninges
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Meninges: The three layers of tissue that encase the CNS: the dura mater, arachnoid membrane, and pea mater.
o Protective sheaths around the brain
o Dura Mater: the outermoust of the meninges, tough and flexible.
o Arachnoid Membrane: Middle layer, located between the other two.
o Pia Matter: Inner layer, clings to the surface of the brain.
 Follows every surface convolution
 Contains smaller surface blood vessels of the CNS
o Subarachnoid Space: The fluid-filled space that cushions the brain; located between the arachnoid
membrane and the pia mater.
 Cerebrospinal Fluid – clear fluid, similar to blood plasma, fills ventricular system of the brain
and subarachnoid space.
o PNS has only two layers – dura mater and pia mater, which fuse and form a sheath that covers the PNS
structures.
Ventricular system and production of CSF
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Brain is soft and jellylike, weighs 1400g.
Brains are well protected
o Floats in a bath of CSF fluid, and being immersed in fluid reduces its net weight to 80g, diminishing
pressure. CSF also reduces shock.
Brains contain Ventricles: Hollow spaces in the brain, filled with CSF fluid.
o Lateral ventricles (first and second) – largest ventricles, one of two located in the center of the
telencephalon, connected to third ventricle.
o Third ventricle – located in the center of the diencephalon, the middle of the brain. Divides surrounding
brain into symmetrical halves.
 Massa intermedia - neural tissue that crosses through middle of third ventricle and serves as a
reference.
 Cerebral aqueduct – long tube that connects third ventricle to fourth ventricle, located in center
of mesencephalon.
o Fourth ventricle – the ventricle located between the cerebellum and the dorsal pons, in the center of the
metencephalon.
Choroid plexus – vascular tissue that protrudes into the ventricles and produces CSF. Located in lateral ventricles.
CSF
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Constantly produced, 125mL total, 3hour half life (meaning within three hours the volume has decreased to half
its original amount and more needs to be made).
Produced by choroid plexus
CSF Flow: Lateral ventricles  third ventricle (more produced here) through cerebral aqueduct  fourth
ventricle (more is produced here) Leaves through small openings  through subarachnoid spacearound CNS.
Reabsorbed into the bloodstream by arachnoid granulations
o Arachnoid granulation: Small projections of the arachnoid membrane through the dura mater into the
superior sagittal sinus; CSF flows through them to be reabsorbed into the blood supply.
o Superior sagittal sinus: A venous sinus located in the midline just dorsal to the corpus callosum,
between the two cerebral hemispheres.
If CSF flow gets blocked, for instance by a tumor, there is increased pressure within the ventricles, since CSF will
continue to be produced. Causes obstructive hydrocephalus when the ventricle walls expand.
o
Obstructive hydrocephalus: A condition in which all or some of the brains ventricles are enlarged,
caused by an obstruction that impedes the normal flow of CSF. Could cause permanent brain damage if
pressure isn’t reversed.
 Drilling a hole and inserting a tube into one of the ventricles, which is connected to a pressure
release valve permanently, can work to allow CSF to escape.
Central Nervous System
Development of CNS
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CNS begins in embryonic life as a hollow tube. During development, tube elongates, pockets and folds form, and
tissue thickens.
Overview of Brain Development
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18th day after conception, nervous system begins developing, forming out of the back of the embryo into a plate
whose edges form ridges that curl toward each other and fuse together by the end of the 21st day.
o Neural tube: A hollow tube, closed at the rostral end, that forms from ectodermal tissue early in
embryonic development; serves as the origin of the CNS.
28th day – neural tube is closed, rostral end has developed 3 interconnected chambers which become ventricles.
Tissue around these chambers become the forebrain, the midbrain, and the hindbrain.
The rostral chamber (forebrain) divides into three parts, which become two lateral ventricles and third ventricle
Regions around ventricles become telencephalon, and region around the third ventricle becomes diencephalon.
Chamber inside the midbrain forms cerebral aqueduct, and two structure develop in hindbrain, the metencephalon
and the myelencephalon.
Details of Brain Development
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Cerebral cortex: The outermost layer of gray matter of the cerebral hemispheres.
o 3mm thick, surrounds cerebral hemispheres, larger in humans than other species, role in cognition and
control of movement.
Ventricular zone: a layer of cells that line the inside of the neural tube; contains progenitor cells that divide and
give rise to cells of the CNS.
o Cerebral cortex is built from this zone, from the inside out.
START OF DEVELOPMENT OF CORTEX :
During the first phase of development, progenitor cells divide and multiply, increasing the size of the ventricular
zone.
o Progenitor cells: Cells of the ventricular zone that divide and give rise to cells of the CNS.
Symmetrical Division: Division of a progenitor cell that gives rise to two identical progenitor cells; increases the
size of the ventricular zone and hence that brain that develops from it.
Asymmetrical division: Division of a progenitor cell that gives rise to another progenitor cell and a neuron,
which migrates away from the ventricular zone toward its final resting place in the brain.  after 7 weeks
o Radial Glia: Special glia with fibers that grow radially outward from the ventricular zone to the surface
of the cortex; provide guidance for neurons migrating outward during brain development.
 Glia extend from ventricular zone and attach to pia mater and these connections are maintained as
cortex grows
 Glia are the first type of brain cells produced through asymmetrical division.
o Cajal-Retzius cells: Specialized neurons that establish themselves during cortical development in a layer
near the terminals of the radial glia, just inside the pia mater; secrete a chemical that controls the
establishment of migrating neurons in the layers of the cortex.
 Second type of brain cells produced through asymmetrical division
o
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Layers: After the first layer of CR cells, a second set of neurons is produced and forms a layer just
beneath. This layer is the innermost of six layers of the cortex. As neurogenesis continues, cells leave the
ventricular zone and pass the layers that have already been made, establishing the next cortical layer,
guided by glial cells.
 Chemicals secreted by CR cells cause neurons to detach and establish themselves in the
outermost layer.
o Asymmetrical division lasts about 3 months
o One billion per day
o Last layer of cells migrate for about 2 weeks (have to pass through many layers).
END OF DEVELOPMENT OF CORTEX:
Cortical development ends when progenitor cells get a chemical signal that causes them to die;
o Apoptosis: Death of a cell caused by a chemical signal tat activates a genetic mechanism inside the cell.
At this time, some radial glia undergo apoptosis, but many are transformed into astrocytes or neurons.
After migrating to final location, cells form connections, grow dendrites and axons. Some extend dendrites
laterally, or even to distant areas of the brain.
Growth of axons: guided by physical/chemical factors, form branches once reached their targets, and each branch
establishes a synaptic connection.
o Cells and cell parts secrete different chemicals to attract certain types of axons to their membrane to
create a synaptic connection. These chemical signals are related to the type of postsynaptic receptors the
cell has.
More neurons than are needed are created, and 50% of axons do not find connections and die. Why? Chemical
signal is sent to cell to allow it to survive only if it reaches a postsynaptic membrane. If a cell can’t find a spot on
the membrane, it doesn’t receive life sustaining signal.
What factors control pattern of development that allows certain regions of the brain to receive specific inputs?
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1. Genetic programming that determines which glial fiber the cell follows, determined by which progenitor cell
the neuron comes from (all neurons from one progenitor cell follow the same fiber)
2. By the axons themselves - Specialization of specific regions can be induced by the axons that give the input to
that region.
o Krubitzer et al removed some cerebral cortex from an opposum early in development, before receiving
input from thalamus, Found that the boundaries of specialized regions were different from those seen in a
normal brain (regions were squeezed in)  growth of axons from a particular region affected
development of the cortical region they served.
3. Experience - Experience affects brain development. Different views from each eye provide a depth cue, called
stereopsis, and neural circuits necessary for this cue will not develop unless the infant has experience viewing
objects with both eyes. There is a critical period for this, 1-3 years.
4. Rewiring after development, as an adult, can occur.
o Amputated arm, region of cortex associated with analyzing info from that limb will start analyzing info
from adjacent areas and may actually become more sensitive.
o Musicians have a larger cortical area devoted to information coming from the hand they use.
Appears that neurogenesis does occur in adults, adult brain contains some stem cells that can divide and produce
neurons.
o Tested using radioactive nucleotide base that cells need for neurogenesis, and then tracing the
radioactivity.
o Results: hippocampus and olfactory bulb, are two areas that contain stem cells.
Evolution of the Human Brain
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Evolution brought about changes that led to more complex brains in later animals.
Genetic Duplication – Most genes perform important functions, and if a mutation causes one of them to do
something new, previous function will be lost. Some genes can be duplicated, and the offspring will get two
versions of the same gene, which leaves room for a mutation to occur that could be beneficial.
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Our brains are larger than other animals. What creates large brain? Rakic; Difference may be due to very simple
process. Since size of brain is determined by size of ventricular zone, and symmetrical division doubles the
number of progenitor cells, a larger brain is due to more symmetric divisions, or delay in termination of the
symmetrical and asymmetrical periods of development. This could be controlled by only a few simple genes that
control timing of brain development.
o i.e, human brain 10x larger than rhesus macaque monkey brain, this is equal to three or four additional
symmetric divisions. Lasts two days longer in humans.
Possible genetic differences – we are unsure about genetic differences that cause our larger brains, but we have
some ideas.
o B-catenin protein regulates cell division and tissue growth, and may also play a role in determining size of
cerebral cortex by controlling symmetrical division.
o Chenn and Walsh – higher levels of B-catenin in progenitor cells of mouse fetuses. Number of progenitor
cells increases dramatically, and mice developed larger brains and larger heads.
o Follow up study – interfering with B-catenin led to a smaller cerebral cortex.
The Forebrain
- Forebrain: The most rostral of the three major divisions of the brain; includes the telencephalon and diencephalon.
Surround rostral end of neural tube.
Telebcephalon
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Telencephalon: most of the two cerebral hemispheres in the cerebrum. The two hemispheres are covered by the
cerebral cortex, and contain the limbic system and the basal ganglia, which are subcortical regions of the brain.
Cerebral Hemispheres: Two major portions of the forebrain, covered by the cerebral cortex (development of
cerebral cortex detailed above)
Subcortical Region: Region located in the brain, beneath cortical surface.
Cerebral Cortex
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Surrounds cerebral hemispheres
In humans, greatly convoluted, with three types of grooves that enlarge the surface area of the cortex, in
comparison to a smooth brain. 2/3 of surface of cortex hidden in these grooves.
o Sulci: A groove in the surface of the cerebral hemisphere, small.
o Fissures: A major or larger groove in the surface of cerebral hemisphere.
o Gyri: A convolution of the cortex of the cerebral hemispheres, separated by sulci or fissures.
2360cm2 in total, 3mm thickness
Consists of glia, cell bodies, dendrites, and axons, but cell bodies predominate, giving it a gray appearance 
grey matter
Below cortex, “in” the brain, axons predominate  white matter
Sensory Receiving Areas
o 1. Primary Visual cortex: Region of posterior occipital lobe with primary input from visual system.
Inner surface of cerebral hemispheres, on banks of the calcarine fissure.
 Calcarine Fissure: Fissure located in the occipital lobe on the medial surface of the brain.
o 2. Primary Auditory cortex: Region of superior temporal lobe that receives input from auditory system.
Located on lower surface of the lateral fissure.
 Lateral Fissure: Separates temporal lobe from the overlying frontal and parietal lobe.
o 3. Primary Somatosensory cortex: Region of anterior parietal lobe whose primary input is from the
somatosensory system. Caudal to central sulcus. Different regions receive information from different
body parts. Some taste information is received at the base of the somatosensory cortex, along with a
portion of the insular cortex.
 Central Sulcus: The sulcus that separates the frontal lobe from the parietal lobe. Separates
somatosensory cortex from motor cortex. Also separates caudal from rostral cerebral cortex.

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-
-
-
-
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Insular Cortex: A sunken region of the cerebral cortex that is covered and hidden from view by
the rostral superior temporal lobe and caudal inferior frontal lobe.
o Usually, sensory information (vision, hearing, touch) is sent to the sensory cortex in the contralateral
hemisphere (except olfaction and gustation)
Primary Motor Cortex: Region of the posterior frontal lobe that contains neurons that control movements of
skeletal muscles. Part of cerebral cortex most involved in the control of movement. Located just in front of the
somatosensory cortex.
o Connections of cells in the motor cortex to muscles in different parts of the body are contralateral.
o Each part of motor cortex associated with a particular part of the body.
Sensory and motor cortexes occupy a small region of cerebral cortex, the rest perform learning, perceiving,
remembering, planning, and acting.  association areas
o Rostral region – movement-related activities (planning and executing behaviors)
o Caudal region – perceiving and learning
o Separated by central sulcus.
Cerebral cortex is divided into lobes
o Frontal Lobe: Anterior portion of cerebral cortex, rostral to parietal lobe, and dorsal to temporal lobe. 
everything front of central sulcus
o Parietal Lobe: Caudal to the frontal lobe, and dorsal to the temporal lobe.  on the side
o Temporal Lobe: Rostral to occipital lobe and ventral to the parietal and frontal lobes.  forward from
base of the brain
o Occipital Lobe: Caudal to parietal and temporal lobes. back of brain
Primary sensory areas send info to adjacent (or near) regions in the cortex, these regions are called: Sensory
Association Cortex: Regions of the cerebral cortex that receive information from the regions of primary sensory
cortex (auditory, visual, somatosensory).
o These regions analyze the information  create perception  create and store memories
o These regions make it possible to integrate information from more than one sensory system
o In the posterior part of the brain
Damage to somatosensory association cortex  deficits related to somatosensation and to environment in general,
because it is an association area that integrates information.
o Unable to name parts of their bodies or perceive shapes they are holding.
o Ex: Mr. M, city bus driver, couldn’t understand what lady was saying and his speech wasn’t making sense
either. MRI showed Mr. M had intracerebral hemorrhage that had damaged his left parietal lobe. Couldn’t
identify body parts at all after, although his speech returned and he could understand what was being told
to him.
Frontal Association Cortex – involved in planning and execution of movements.
o Motor Association Cortex: Region of frontal lobe rostral to primary motor cortex, aka prefrontal cortex.
Controls primary motor cortex, so controls behavior.
o Prefrontal cortex: Rest of the frontal lobe, rostral to motor association cortex. Less involved with control
of movement and more involved with formulating plans and strategies.
The two cerebral hemispheres (left and right) sometimes work together, but some functions are lateralized
functions, located on one side of the brain.
o Left hemisphere – analysis of information (extracting info), good at sequences of events.
 Verbal activities: reading, writing, speaking
o Right hemisphere: synthesis, putting isolated elements together to create wholes.
 Drawing sketches
We are unaware that the two hemispheres operate separately, we have unified memories and perceptions, this is
accomplished by corpus callosum
o Corpus Callosum: Large bundle of axons that interconnects corresponding regions of the association
cortex on each side of the brain. Mostly symmetric connections (parietal lobe to parietal lobe, etc), but
some asymmetrical connections, too.
Neocortex: Phylogenetically newest cortex including primary sensory cortex, primary motor cortex, and
association cortex. Covers most of the surface of the cerebral hemispheres.
Limbic System: Phylogentically old cortex, located at the medial edge of the cerebral hemispheres; part of the
limbic system.
Cingulate Gyrus: A strip of the limbic cortex lying along the lateral walls of the groove separating the cerebral
hemispheres, just above the corpus callosum.
Limbic System
-
-
Papez, first hypothesized about a set of interconnected brain structures that controlled motivation and emotion.
MacLean, expanded the system, and coined it the limbic system.
Limbic System: A group of brain regions including the anterior thalamic nuclei, amygdale, hippocampus, limbic
cortex, and parts of the hypothalamus, and was as their interconnecting fiber bundles. Most important part besides
limbic cortex is hippocampus and amygdala.
Hippocampus: A forebrain structure of the temporal lobe, constituting an important part of limbic system;
includes the hippocampus proper, dentate gyrus, and subicum.
Amygdala: A structure in the interior of the rostral temporal lobe, containing a set of nuclei; part of the limbic
system.
Fornix: A fiber bundle that connects the hippocampus with other parts of the brain, including the mammillary
bodies of the hypothalamus; part of limbic system.
o Mammillary bodies: A protrusion of the bottom of the brain at the posterior end of the hypothalamus,
containing some hypothalamic nuclei; part of limbic system.
Evolution of this system coincided with development of emotional responses.
Basal Ganglia
-
Basal Ganglia: A group of subcortical nuclei in the telencephalon that lie below the anterior portion of the lateral
ventricles. Major parts include: the caudate nucleus, the globus pallidus, and the putamen; important parts of the
motor system.
Involved in control of movement
Parkinson’s disease is caused by degeneration of neurons that send axons to the caudate nucleus and the putamen.
Diencephalon
-
Diancephalon: Major division of the forebrain, surrounds the third ventricle, includes thalamus and
hypothalamus. In between telencephalon and mesencephalon.
Thalamus
-
-
-
Thalamus: The largest portion of the diencephalon, located above the hypothalamus; contains nuclei that project
information to specific regions of the cerebral cortex and receive information from it.
Dorsal part of diencephalons.
Location: near middle of cerebral hemispheres, medial and caudal to the basal ganglia.
Has two lobes connected by massa intermedia, a bridge of grey matter that in some people is missing.
Sends neural input to cerebral cortex through projections
o Projections: An axon of a neuron in one region of the brain whose terminals form synapses with neurons
in another region.
o Specific portions of the cerebral cortex receive projections from specific parts of the thalamus.
Divided into nuclei
o Sensory nuclei – receive info from sensory system and relay the information to specific parts in cerebral
cortex
 Lateral geniculate nucleus – receives information from the eye and relays it to primary visual
cortex
 Medial geniculate nucleus – receives information from the inner ear and sends info to primary
auditory cortex.
o Nonsensory info
 Ventrolateral nucleus – receives information from cerebellum and send info to motor cortex
 Some nuclei receive and send within the cerebral cortex
General widespread projections to all cortical regions
Hypothalamus
-
Hypothalamus: The group of nuclei of the diencephalons situated beneath the thalamus at the base of the brain;
involved in regulation of the autonomic nervous system, control of the anterior and posterior pituitary glands, and
integration of species typical behavior (four F’s).
Basic functions: autonomic nervous system control, endocrine system control, organizes behaviors related to
survival.
Situated on both sides of ventral portion of third ventricle.
Pituitary gland is attached at the base of the hypothalamus via pituitary stalk
Optic Chiasm: An X-shaped connection between the two optic nerves, located below the base of the brain, just
anterior to the pituitary gland. Optic nerves cross over here.
Hypothalamus creates hormones that control endocrine system, through a special system of blood vessels that
connects hypothalamus with anterior pituitary gland and posterior pituitary gland, thereby controlling their
secretions.
o Anterior Pituitary gland: The anterior part of the pituitary gland; an endocrine gland whose secretions
are controlled by the hypothalamic hormones. Its secretions control endocrine glands (gonadrotopic
hormones stimulate gonads to release male or female sex hormones)
o Neurosecretory cells: Secrete hypothalamic hormones, these cells are located near the base of the
pituitary stalk and stimulate anterior pituitary gland to release its hormones.
o Posterior Pituitary Gland: The posterior part of the pituitary gland; an endocrine gland that contains
hormone-secreting terminal buttons of axons whose cell bodies lie within the hypothalamus. The axons
travel down the pituitary stalk and the vesicles varying the hormones collect in this gland.
 Ex: oxytocin, a secretion of the hypothalamus, stimulates the posterior pituitary gland to release
vasopressin which regulates urine output.
The Midbrain
-
Midbrain: The mesencephalon; the central of the three major divisions of the brain.
Tectum
-
-
Tectum: The dorsal part of the midbrain; includes the superior and inferior colliculli which appear as four bumps
on the dorsal surface.
o Superior Colliculi: Protrusions on the top of the midbrain, part of the visual system.
o Inferior colliculi: Protrusions on the top of the midbrain; part of the auditory system.
Brain stem includes midbrain and hindbrain and looks like a stem
Tegmentum
-
-
Tegmentum: The ventral part of the midbrain; includes the periaqueductal gray matter, reticular formation, red
nucleus, the substantia nigra, and the ventral tegmental area.
Beneath tectum
Reticular Formation: A large network of neural tissue located in the central region of the brain stem, from the
medulla to the diencephalons.
o Contains lots of nuclei and interconnected network of neurons
o Occupies core of brain stem
o Connects with cerebral cortex, thalamus, and spinal chord and receives sensory information from these
areas
o Functions: arousal, attention, sleep
Periaqueductal gray matter: The region of the midbrain surrounding the cerebral aqueductal contains neural
circuits involved in species-typical behaviors.
o Mostly cell bodies of neurons
-
Red nucleus: A large nucleus of the midbrain that receives inputs from the cerebellum and motor cortex and
sends axons to motor neurons in the spinal cord.
Substantia Nigra: A darkly stained region of the tegmentum that contains neurons that communicates with the
caudate nucleus and putamen in the spinal chord.
The Hindbrain
-
Hindbrain: The most caudal of the three major divisions of the brain; includes the metencephalon and
myelencephalon.
Mentacephalon
-
consists of pons and cerebellum
Cerebellum
-
Cerebellum: A major part of the brain located dorsal to the pons, containing the two cerebellar hemispheres,
covered with the cerebellar cortex and important component of the motor system.
o Cerebellar cortex: The cortex that covers the surface of the cerebellum.
Contains deep cerebellar nuclei: Nuclei located within the cerebellar hemispheres; receives projections from the
cerebellar cortex and sends projections out of the cerebellum to other parts of the brain.
Each hemisphere is attached to the pons by bundles of axons
o Cerebellar peduncles: Three bundles (superior, middle and inferior) of axons that attach cerebellar
hemispheres to dorsal pons.
Cerebellum receives visual, auditory, vestibular, somatosensory information, and info about muscle movements,
and integrates all this information to modify motor outflow, allowing for coordinated and smooth movements.
Damage to this structure impairs standing, walking, coordinated movements
Pons
-
Pons: The region of the metencephalon rostral to the medulla, caudal to the midbrain, and ventral to the
cerebellum.
Contains portion of reticular formation including nuclei for sleep and arousal
Contains large nucleus that relays information from cerebral cortex to cerebellum.
Myelencephalon
-
Contains medulla oblongata: the most caudal portion of the brain; located in the myelencephalon, immediately
rostral to the spinal cord.
Contains part of reticular formation, including nuclei that control cardiovascular system, respiration, and skeletal
tonus.
The Spinal Chord
-
Spinal cord: Cord of nervous tissue that extends caudally from the medulla.
Principal function is to distribute motor fibers to effector organs and to collect information for the brain
Controls some reflexive circuits, separate from the brain
Protected by vertebral column composed of individual vertebrae in the neck/cerival, chest/thoracic, and
lowerback/lumbar regions, and fused vertebrae of the sacral and coccygeal portions (pelvis)  spinal cord passes
through a hole in this structure.
-
Spinal roots: A bundle of axons surrounded by connective tissue that occurs in pairs, which fuse and form a
spinal nerve.
Cauda Equina: a bundle of spinal roots located caudal to the end of the spinal cord.
Spinal roots and cauda fill up empty space at the end of the vertebrae that the spinal cord doesn’t fill (vertebral
column grows a little faster than the spinal cord)
Caudal block: the anesthesia and paralysis of the lower part of the body produced by injection of a local
anesthetic into the cerebrospinal fluid surrounding the cauda equina. Blocks conduction in the axons.
Dorsal roots: Spinal root that contains incoming sensory fibers.
Ventral roots: the spinal root that contains outgoing motor fibers.
Meninges cover the spinal cord, and small bundles of fibers emerge from each side of the spinal cord to create the
dorsal and ventral roots, which fuse together to form spinal nerves.
Contains white matter and grey matter – white matter on the outside
Peripheral Nervous System
-
Conveys information to the CNS, and sends info from CNS to body
Communication occurs via cranial and spinal nerves
Somatic nervous system: the part of the peripheral nervous system that control the movement of skeletal muscles
or transmits somatosensory information to the central nervous system.
Autonomous nervous system: the portion of the peripheral nervous system that controls the body’s vegetative
functions.
Spinal Nerves
-
Spinal Nerves: A peripheral nerve attached to the spinal cord. Begin at junction of dorsal and ventral roots, leave
vertebral column and go to muscles/sensory receptors.
Branches of these often follow blood vessels
Pathway of sensory info entering spinal cord/motor information leaving spinal cord
Afferent axons (axon directed towards CNS, conveys sensory info) belong to dorsal root ganglia (a nodule on a
dorsal root that contains cell bodies of afferent spinal nerve neurons) that are unipolar neurons that have one stalk
inside the spinal cord and one axon out toward the sensory organ.
Efferent axons (an axon directed away from the central nervous system, conveying motor commands to muscles
and glands) leave the spinal cord through ventral roots, which joins a dorsal root to make a spinal nerve. The cell
bodies of efferent axons are in the grey matter.
Cranial Nerves
-
Cranial nerves: A peripheral nerve attached directly to the brain, to the ventral surface. Serve sensory functions
of the head and neck region.
Receive somatosensory and taste information from the unipolar neurons
Receive auditory, vestibular, and visual information from bipolar neurons
Receive olfactory information from the olfactory bulb
o Olfactory bulb: the protrusion at the end of the olfactory nerve; receives input from the olfactory
receptors.
Vagus nerve: The largest of the cranial nerves, conveys efferent fibers of the parasympathetic division of the
autonomic nervous system to organs of the thoracic and abdominal cavities.
Autonomic Nervous System (the portion of the peripheral nervous system that controls the body’s vegetative functions.)
-
Concerned with movement of smooth muscle, cardiac muscle, and glands (as opposed to skeletal muscle, which is
the somatic nervous system).
Two systems – sympathetic division and parasympathetic division
Sympathetic division of the ANS
-
-
Sympathetic division: The portion of the autonomic nervous system that controls functions that accompany
arousal and expenditure of energy.
Most concerned with activities that expend energy reserves
o Ex: when an organism is excited, sympathetic system increases blood flow to skeletal muscles, stimulates
secretion of epinephrine and causes piloerection.
Cell bodies of these neurons are in gray matter of the thoaracic and limbar regions of spinal cord
Fibers exit ventral roots, join spinal nerves, and branch off into sympathetic ganglia (nodules that contain
synapses between preganglionic and postganglionic neurons of the sympathetic nervous system.
Sympathetic ganglion chain: one of a pair of groups of sympathetic ganglia that lie ventrolateral to the vertebral
column.
Preganglionic neurons: the efferent neuron of the autonomic nervous system whose cell body is located in a
cranial nerve nucleus or in the intermediate horn of the spinal gray matter and whose terminal buttons synapse
upon postganglionic neurons in the autonomic ganglia.
Postganglionic Neurons: Neurons of the autonomic nervous system that form synapses directly with their target
organ.
Adrenal Medulla: The inner portion of the adrenal gland, located atop the kidney, controlled by the sympathetic
nerve fibers; secretes epinephrine and norepinephrine.
o VERY similar to sympathetic ganglion because it receives input from preganglionic cells and innervated
by postganglionic cells
o These hormones that are released function in coordination with the sympathetic system, like by increasing
blood flow to the muscles.
Acetylcholine released by preganglionic cells, norepinephrine by postganglionic cells.
Parasympathetic Division of the ANS
-
Parasympathetic division: the portion of the autonomic nervous system that controls functions that occur during
a relaxed state.
Activities that help increase the body’s supply of stored energy
o i.e. salivation, secretion of digestive juices, etc.
Cell bodies located in cranial nerves and gray matter of sacral region of spinal cord.
Parasympathetic ganglia located very close to target organ
Neurotransmitter is acetylcholine for both types of cells (post and pre).
Questions:
1. What is the importance of CSF fluid, and detail its path and production in the brain. What happens if the flow of
CSF is blocked?
Question 2: Outline the differences between the autonomic and somatic nervous systems.
Question 3: Which part is the most caudal of the three main divisions of the brain?
Answer 1 :
-
CSF protects the brain
CSF Flow: Lateral ventricles  third ventricle (more produced here) through cerebral aqueduct  fourth ventricle (more
is produced here) Leaves through small openings  through subarachnoid spacearound CNS.
- Reabsorbed into the bloodstream by arachnoid granulations
- If CSF flow gets blocked, for instance by a tumor, there is increased pressure within the ventricles, since CSF will continue to
be produced. Causes obstructive hydrocephalus when the ventricle walls expand.
o Obstructive hydrocephalus: A condition in which all or some of the brains ventricles are enlarged, caused by an
obstruction that impedes the normal flow of CSF. Could cause permanent brain damage if pressure isn’t reversed.
 Drilling a hole and inserting a tube into one of the ventricles, which is connected to a pressure release valve
permanently, can work to allow CSF to escape.
Answer 2:
-
Somatic nervous system: the part of the peripheral nervous system that control the movement of skeletal muscles or
transmits somatosensory information to the central nervous system.
Autonomous nervous system: the portion of the peripheral nervous system that controls the body’s vegetative functions.
o Sympathetic division: The portion of the autonomic nervous system that controls functions that accompany arousal
and expenditure of energy.
o Parasympathetic division: the portion of the autonomic nervous system that controls functions that occur during a
relaxed state.
-
Answer 3: Hindbrain
Introduction to Behavioural Neuroscience Chapter 4
SEPARATE PAGE
Neuroscience- Chapter 5

o
Introduction
Story





o
o
1982-young people going to neurology clinics in California with severe symptoms (looked like
Parkinson's, but not cuz Parkinson's is gradual and usually only older)
Common factor= had been taking a "new heroin" (contaminated with a chemical that damaged
dopaminergic neurons)
Gave L-DOPA (used to treat Parkinson's)- only temporary improvement
Instead, FETAL TRANSPLANTATION (neurosurgical method to treat Parkinson's)

Since caused by lack of dopamine in caudate nucleus/putamen in both cases, put
dopamine-secreting neurons into these places so symptoms will diminish

Used neurons from aborted human fetuses
Ex: Patient

Got injection of L-DOPA

Put in PET scanner- info from positrons being emitted as radioactive particles broke
down in head

Few weeks later, implanted dopaminergic neurons into brain

Made cuts in brain, attached stereotaxic apparatus to skull, drilled holes

Used stereotaxic apparatus to guide injections

SUCCESSFUL!-year later: put in PET scanner again and showed cells had survived and
were secreting dopamine
Need to know advantages/limitations of methods
Best: compare results of studies with different methods

Experimental Ablation
 Destroy part of brain and then evaluate behaviour (usually destroy tissue, but leave it in his place (don't
remove))
Oldest
method, yet common

o
Evaluating the Behavioural Effects of Brain Damage
LESION: wound/injury

Researcher who destroys part of brain refers to damage as BRAIN LESION

LESION STUDIES: experiments where part of brain is damaged and animal's behaviour is

observed
Want to discover what functions are performed by different regions of brain and what functions

are combined for different behaviours

Circuits within brain perform functions (not behaviours)
Ex: act of reading involves functions for controlling eye movements...

Some functions participate in other behaviours

No one region is solely responsible for a behaviour


Must understand functions needed for different behaviours and what circuits of neurons
are responsible
Hard because all regions are interconnected


so if find damage to X impairs certain behaviour, doesn't mean function is for sure
performed in X (could mean damage to X impairs neural circuits of Y)
o
Producing Brain Lesions
When want to destroy parts of brain immediately beneath skull


Anesthetize animal, cut scalp, remove part of skull, cut through dura mater so see cortex,
place glass pipette on surface of brain and suck away brain tissue with vacuum pump attached to
pipette
When regions are deep in brain (in subcortex)


Method 1
Pass electrical current through wire that is coated with varnish except for tip

Guide wire stereotaxically so reach region

Lesion-making device produces radio frequency (RF) current, which produces

heat, which kills all cells, neural cell bodies, and axons surrounding tip or passing through
region (not specific at all)

Method 2: Excitotoxic Lesions
More selective

Excitatory amino acid (kainic acid) is injected through cannula, which destroys

neural cell bodies, but spares axons passing by and that belong to other neurons
Researcher can tell whether effects are because of neurons in that region or axons

passing by

Method 3
Even more specific

Attach toxic chemicals to antibodies that bind with particular proteins found only

on certain types of neurons
SHAM LESIONS


Using electrode/cannula causes damage to brain (even before start injection) so can't
compare to unoperated, need control group:

So anesthesize all animals, put in stereotaxic apparatus, cut open scalp, drill holes, insert
cannula/electrode but don't turn on machine/start infusion for control!
To temporarily damage region (others were permanent)


Inject muscimol (stimulates GABA-inhibitory transmitter) into brain, which blocks action
potentials entering/leaving region

Called REVERSIBLE BRAIN LEGION
o
Stereotaxic Surgery

To get electrode/cannula to a specific place in brain

STEREOTAXIC: solid arrangement- ability to locate objects in space

STEREOTAXIC APPARATUS:
contains holder that fixes animal's head to in a standard position




o


and a carrier that moves electrode/cannula through measured distances in all three axes of
space
The Stereotaxic Atlas

Must study to perform stereotaxic surgery

Contains pictures/drawings that correspond to frontal sections taken at various distances
rostral/caudal to bregma

BREGMA
Skull made up of several bones that grow together and form SUTURES (seams)

Heads of newborns contains soft spot (called FONTANELLE) at junction of

coronal and sagittal sutures
Once gap closes, junction is called BREGMA (good reference point)


To get to specific region,
Drill hole through skull above it- each page of stereotaxic atlas is labelled

according to distance of the section anterior or posterior to bregma and grid on each page
shows distances of brain structures ventral to top and lateral to midline
Always relative to skull height at bregma! (with help of stereotaxic atlas)- only

approximate so must slice and stain to test
The Stereotaxic Apparatus

Made for humans

Includes head holder (keeps skull in proper orientation), a holder for the electrode, and a
calibrated mechanism that moves electrode holder along 3 axes (anterior-posterior, dorsal-ventral,
lateral-medial)

Obtain coordinates from atlas, cut scalp open, locate bregma, dial in appropriate numbers
on apparatus, drill hole though skull, and lower device correct amount- then brain scan to make
sure right place before lesioning

Not only for lesioning, can also stimulate neurons or inject particular drugs that
stimulate/block receptors

Sewn together after
Histological Methods

After brain lesion, slice and stain brain so can see location under microscope

HISTOLOGICAL METHODS: fix, slice, stain and examine brain to verify precise location (often
miss mark)
Fixation and Sectioning

First, PERFUSION of tissue
Removal of blood and replacement with dilute salt solution so better histological

methods

Then, place neural tissue in FIXATIVE
Most common fixative: FORMALIN (halts autolysis (turning into mush),

hardens soft brain, and kills microorganisms) so can study in form when animal died

Then, slice into thin sections and stain cellular structures
Slice with MICROTOME (has 3 parts)

Knife
Platform to mount tissue on
Mechanism that advances knife/platform the correct amount so another section
can be cut
Also might have section to freeze brain so easier to cut

Then, attach slices to microscope slides, stain them, add transparent liquid (mounting
medium) to keep coverslip in place
Staining

Different stains to see specific substances within and outside of cell

Cell-body stain:
Nissl discovered methylene blue stains cell bodies of brain tissue
Nissl substance (material that makes up dye consists of RNA/DNA/associated proteins)
Besides methylene blue, other dyes, most frequent: cresyl violet
First used to dye cloth, then identify nuclear masses in brain
Fiber bundles do not take up stain so lighter


o


Stain is not selective for neural cell bodies- neurons and glia are stained so researcher
identifies by size/shape/location
Electron Microscopy

Use TRANSMISSION ELECTRON MICROSCOPE to see small anatomical structures
and details of cell organelles
Beam of electrons pass though tissue
Beam casts shadow on fluorescent screen, which is scanned onto computer
Electron photomicrographs provide lots of detail

SCANNING ELECTRON MICROSCOPE
Provides less detail than transmission one, but shows in 3D
Scans tissue with moving beams of electrons, info is received by detector, and computer
produces 3D view
Confocal Laser Scanning Microscopy

Possible to see details in thick/slabs of tissue (others were for thin)
Cells must be stained with fluorescent dye (immunocytochemistry)
Beam of light is produced by laser and reflected off dichroic mirror (transmits light of
certain wavelengths and reflects others)
Lenses focus at depth and light triggers fluorescence in tissue to pass through lens and go
through pinhole aperture
Aperture blocks extraneous light
Two moving mirrors cause laser light to scan tissue, which provides computer with
information to form image of slice
If multiple scans are made while aperture moved, stack of images of slices
In example, saw loss of dendritic spines after 4 hours

Tracing Neural Connections
Ex: want to study neural mechanisms for reproductive behaviour

First, physiology of sexual behaviour in female rats--> stereotaxic surgery in two groups
of rats (lesion in VMH and sham surgery on control); then put with males and those with lesions
refused to copulate; confirmed with histology that VMH was destroyed in brains

But VMH not alone; what structures send axons to VMH and what structures does VMH
send its axons- to know connections:
Tracing Efferent Axons

We know eventually VMH will affect behaviour (neurons will send axons to part of brain
responsible for muscular movements)

Need to trace EFFERENT AXONS (axons leaving VMH)
Use ANTEROGRADE LABELING METHOD to trace these axons- inject

chemicals into nucleus using stereotaxic apparatus that are taken up by cell bodies (use PHAL for VMH) and are then transported through the axons to the terminal buttons
After a few days, cells/dendrites/soma/axons/branches/terminal buttons are filled

with PHA-L
Then kill animal, slice brain, and mount onto microscopic slides

Use IMMUNOCYTOCHEMICAL METHOD to make PHA-L molecules visible

Immune system produces antibodies (produced by white blood cells) in

response to antigens (proteins on bacteria/viruses)
Have developed method to produce antibodies (which are on dye

molecules) to any peptide/protein (antigen)
Some dyes react with chemicals and stain tissue brown

Others glow when exposed to light of specific wavelength

To see where protein (antigen) is, places slices of tissue that

contains antibody/die molecules
Antibodies then attach to antigens and can see, though

microscope, which parts of brain contain the antigen
In example, showed some efferent axons of VMH terminate in

PAG
So then we'd inject PAG with PHA-L and see where

their axons go, eventually see whole pathway from VMH to motor neurons

Tracing Afferent Axons
For before reaching the VMH (upstream components)
Use RETROGRADE LABELLING METHOD
First, inject small quantity of chemical called FLUOROGOLD into VMH, which

is taken up by terminal buttons and is transported back by retrograde axoplasmic transport to
the cell bodies
A few days later, kill animal, slice its brain, and examine tissue under specific

light
The molecules of fluorogold fluoresce under this light

In example, discovered medial amygdala is one that provides input


TRANSNEURONAL TRACING METHODS
Identify a series of two, three or more neurons that form serial synaptic

connections with each other
Most effective retrograde transneuronal tracing method:

Uses a PSEUDORABIES VIRUS (weakened form of pig herpes virus

that was originally developed as vaccine)
Most effective anterograde transneuronal tracing method:

Uses HERPES SIMPLEX VIRUS (similar to one that causes cold sores)

Virus injected into region and affects neurons there, eventually passed on to other

neurons that form synaptic connections with them
The longer experimenter waits after injecting virus, the larger the number of neurons that become
infected
After animal is killed and brain sliced, immunocytochemical methods used to localize protein
produced by virus
SO anterograde and retrgrade labelling methods-including transneuronal methods- enable us to
discover circuits!
Studying the Structure of the Living Human Brain
Study function of brains of animals so can make inferences about various neural systems in
humans
Diseases/accidents where human brain is damaged- if know where damage, can study behaviour
and make inferences without deliberate damage
But, for long time, wouldn't know where exactly damage was until person died
Now, advances in X-ray techniques/computers to study anatomy of living brain

Method 1: Computerized Tomography (CT)
Head placed in doughnut-shaped ring

Ring contains x-ray tube and an x-ray detector on the other side of the patient's

head
X-ray beam passes though patient's head and detector measures amt of

radioactivity that gets through it
Computer translates numbers into pictures of skull

Along horizontal plane

Figure 5.19 (p.148): damage=white/empty spot in #5


Method 2: Magnetic Resonance Imaging
More detailed, high resolution

Looks like CT machine, but uses strong magnetic field (not x-rays)

Because of magnetic field, nuclei of some atoms in body spin in particular

orientation
If radio frequency wave is then passed though the body, nuclei emit radio waves

of their own at different frequencies
MRI scanner detects radiation from hydrogen atoms- because they're in different

concentrations in brain, scanner prepares pictures of slices of brain
Along horizontal, sagittal, and frontal planes

Distinguishes between gray and white matter so fiber bundles (corpus callosum)

can be seen- small fibers not visible
The higher the temperature, the faster the random movement






o


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


Uses info about movement of water molecules to determine location/orientation
of bundles of axons in white matter

Diffusion Tensor Imaging
Takes advantage of fact that movement of water molecules in bundles of white

matter will not be random--> will move in direction parallel to axons that make up bundles
Computer adds colour to distinguish different bundles of axons

o
***SUMMARY-p. 150***
Recording and Stimulating Neural Activity
 Different behaviours involve different patterns of activity in brain--> methods to record these
patterns:
o
Recording Neural Activity

Recordings can be made during stimulus presentations, decision-making, or motor activities

Can be made
Chronically (over an extended period of time after animal recovers from surgery)

Acutely (for a relatively short period of time during which animal is kept anesthesized)
restricted to studies of sensory pathways, not behavioural observations
Recordings with MICROELECTRODES


Made of thin wires, have a very fine tip, so can record electrical activity of an individual
neuron

Called SINGLE-UNIT RECORDING
Want durable electrodes since recording chronically

Made up of very fine wires, gathered together in bundle, which record activity of

many different neurons - wires= insulated so only tips are bare
Implant electrodes through stereotaxic surgery, then animals plugged into

recording system (behave normally even though sockets on skull)
Can also move electrode around so can record from different parts of brain

Electrical signals form microelectrodes are small and must be amplified (weak-->

strong signals)- displayed on oscilloscope and store in computer
Ex: measured particular neurons during REM sleep and saw firing rates fall to

zero--> have inhibitory effect-->REM sleep occurs when neurons stop firing
Recordings with MACROELECTODES


Record region as whole (not individual neurons) --> represent postsynaptic potentials of
millions of cells in electrode area

Can be unsharpened wires, screws attached to skull or metal disks attached to scalp with
paste that conducts electricity (this one = enormous number)

Sometimes, directly into brain to detect source of abnormal electrical activity leading to
seizures
Can then remove source of seizure


Electrical activity is recorded through electrodes and displayed on polygraph
Moves long strip of paper past series of pens, which move up/down in response

to electrical signal sent to them by biological amplifiers, then shown on computer
ELECTROENCEPHALOGRAM: writings of electricity from the head

can study stages of epilepsy/sleep

To monitor condition of brain during procedures that could damage it

(ex: if having operation)
If brain not receiving enough blood, EEG will show "slow

waves"
Magnetoencephalography


When electrical current flows though conductor, induces magnetic field (as action
potentials pass down dendrites, very small magnetic field is produced)

Have SQUID (superconducting detectors) that can detect these small magnetic fields

Performed with neuromagnetometers (devices that have lots of SQUIDS) so computer
can calculate source of particular signals in brain
Ex: can find source of seizures so it can be removed

Can measure regional brain activity that accompanies behaviours

o
Recording the Brain's Metabolic and Synaptic Activity


o

If neural activity increases, so does metabolic rate (because of increased operation of ion
transporters)
Metabolic rate measured by

Method 1
Injecting 2 DG (like glucose) into blood, which is taken into cells

The most active cells will take up highest concentration of 2 DG, but will not be

metabolized so will stay in cell
The animal is killed, brain is removed, sliced, and prepared for

AUTORADIOGRAPHY
Autoradiography

Sections put on slides in darkroom and coated with photographic

emulsion
After several weeks, 2 DG molecules show as silver grains, most active

(highest metabolic rate) shows as dark spots

Method 2
When neurons are activated, immediate early genes are turned on and particular

proteins are produced, these proteins bind with chromosomes on nucleus, and the presence of
these nuclear proteins indicates neuron is activated
FOS= nuclear protein

If wanted to use to see how neurons are activated during female rat's

sexual behaviour, let females and males copulate
Then, remove rat's brains, slice them, and stain Fos protein (dark spots

indicate Fos on those neurons)

FUNCTIONAL IMAGING (computerized method to detect metabolic/chemical changes
in brain) - 2 kinds
Method 3: POSITRON EMISSION TOMOGRAPHY (PET)

Receives injection of 2-DG (leaves in 2-110 mins); head placed in CT

scanner; when 2 DG molecules decay, emit positrons detected by scanner; comp
determines which region took up substance, and produces picture of slice with different
activity levels for places in that slice
Disadvantages: expensive, poor spatial resolution, poor temporal

resolution
Since decay so quick, must be produced on site in CYCLOTRON to

accelerate(more money)
Advantage: can measure concentration of particular chemicals in various

parts of brain (fMRI can't)
Method 4: FUNCTIONAL MRI (fMRI)

Best spatial and temporal resolution, indicate regional metabolism

Activity measured indirectly- detect levels of oxygen in blood vessels

Increased activity stimulates blood flow to that region, which

increases local blood oxygen level
Formal name is BOLD (blood oxygen level dependent signal)

Stimulating Neural Activity

Artificially change activity of regions to see effects on behaviour
Electrical and Chemical Stimulation (to activate neurons)

Electrical stimulation: pass electrical current through wire inserted into brain

Chemical stimulation: inject amino acid into brain (principle excitatory neurotransmitter:
glutamate, kainic also used)- stimulate glutamate receptors-activates neurons on these
Injections are with apparatus that is permanently attached to skull so can observe

behaviour
Put cannula in and cement to top of skull

Then, another day, put smaller cannula in that one and inject chemical into brain

Since animal is free to move, can observe behaviour

More complicated than electrical (need more materials), but activates cell bodies

in that regions (not axons passing though) cuz only cell bodies contain glutamate receptors
(unlike electrical)--> more localized

Kainic usually stimulates to death, but when small doses of dilute is used, it just
stimulates them
In example, stimulating VMH does substitute female sex hormones

(they copulated)
Photostimulation


To stimulate or inhibit certain types of neurons in particular brain regions (so don't
activate everything around)

Photosensitive proteins
Channelrhodopsin-2 (ChR2) (in green algae)

permits flow of sodium, potassium, and calcium ions

When blue light strikes, channel opens, and positively charged

sodium/calcium depolarizes membrane
Natronomaonas pharaonis halorhodospin (NpHR) (found in bacterium)

Controls transporter that moves chloride into cell when activated by blue

light
Since negative, hyperpolarizes membrane

Both need right wavelength and happens quickly

Both are put in neuron by attaching genes that code for them into genomes of

harmless viruses, viruses injected and will affect certain neurons
Both need light so if in

Cerebral cortex: small hole drilled in skull and LED's (light emitting

diodes) are attached to hole
Depths of brain: optical fibres implanted with stereotaxic surgery and

light transmitted through fibers
This way, can study certain neural circuits and may help treat problems (ex:

blindness, Parkinson's)
Transcranial Magnetic Stimulation


Uses coil of wires in 8 formation to stimulate neurons in cerebral cortex

Placed on top of skull so crossing point is just above region to be stimulated

Pulses of electricity send magnetic fields activating neurons in cortex

Effects similar to those of direct stimulation of exposed brain
o
***SUMMARY-p.159***
Neurochemical Methods
 To get locations of neurons that possess particular types of receptors, to measure amount of chemicals
secreted by neurons in particular region
o
Finding Neurons that Produce Particular Neurochemicals
Ex: farmers exposed to certain types of insecticides had bizarre dreams, know this drug acts at

acetylcholinergic synapses- what neurochemical methods can be used to discover sites of action of drugs
in brain?
Localize particular neurochemicals (like neurotransmitters/neuromodulators)
In example, look for neurons containing acetylcholine
Either
Localize chemicals themselves

Localize enzymes that produce them

Localize messenger RNA involved in synthesis

Peptides/proteins can be localized with immunocytochemical method (acetylocholine is
not peptide so use immunocytochemical method to localize enzymes that produce it- ChAT)
IN SITU HYBRIDIZATION
When protein producd, info copied onto messenger RNA, which travels to ribosome
where protein synthesis takes place
Can synthesize piece of radioactive RNA containing nucleotides complementary to
sequence on messenger RNA
Then use autoradiographic methods to reveal location of messenger RNA
o
Localizing Particular Receptors
Since neurotransmitters convey messages by binding to receptors, location of these receptors

must be determined:
1.
Using Autoradiography
Expose brain slice to solution with radioactive ligand for particular receptor
Then, rinse to only ligand bound to their receptors is left
Use autoradiography to localize radioactive ligand and its receptors
2.
Using Immunocytochemistry
Receptors are proteins so can produce antibodies against them

Expose slice to appropriate antibody (shown with fluorescent die) and look at

slices with microscope under light of particular wavelength
Ex: put small amount of sex hormone into VMH in rats whose ovaries

had been removed--> hormone does reactivate sex behaviour
Ex: use audiography to look for receptors for sex hormone- expose slices

to radioactive hormone, rinse them, and perform audiography--> would find
radioactivity in VMH
Ex: could use immunocytochemistry to localize hormone receptors and

get same results
o
Measuring Chemicals Secreted in the Brain
Dialysis: process where substances are separated by means of artificial membrane that is

permeable to some molecules, but not others
Microdialysis:


Small metal tube inserted through stereotaxic surgery

Put solution (like extracellular fluid) into section of dialysis tubing

Fluid circulated in dialysis tubing

Then passes through other small metal tube, which leads solution away so can analyse
with sensitive analytical method (can detect neurotransmitters that have been released from
synaptic cleft into extracellular fluid

Not on humans yet (only those with head trauma)- use PET instead
In fig. 5.38 (p.164)- shows amount of radioactivity before and after transplant

(shown in fluorescent colour)
o
***SUMMARY-p.165***
Genetic Methods
 All behaviour depends on interaction between brain and environment
 Many behavioural characteristics (talents/personality/disorders) run in family --> genetic factors
 Sometimes, defective gene interferes with brain development and neurological abnormality causes
behavioural deficits
 Other cases, need genetic methods to see links between heredity and behaviour
o
Twin Studies
Compare concordance rate for trait in pairs of monozygotic (identical genotypes-chromosomes

are same) and dizygotic twins (fraternal-genetic similarity= 50%)
If both twins diagnosed with disorder, they are CONCORDANT

If only one, called DISCONCORDANT

If genetic, % of monozygotic who are concordant will be higher than dizygotic


Ex: schizophrenia is 4 times more likely in monozygotic so heritable
o
Adoption Studies
Compare people adopted early in life with biological parents- genetic associated with biological

parents and postnatal environment associated with adoptive parents
Environmental (social/biological) (prenatal/postnatal)

If resemble biological parents, it's probably genetic (also need to rule out possible differences in

prenatal environment of adopted children)
If resemble adoptive parents, trait influenced by environment

If resemble both, it's influences by both

o
Targeted Mutations
Mutated genes produced in lab and inserted into chromosomes of mice- they're defective (don't

produce functional protein)
Can also produce conditional knockouts (cause genes to stop expressing particular gene when

animal is given certain drug)
Genes can also cause increased production of proteins or can produce completely new proteins





o




Antisense Oligonucleotides
Blocks production of proteins encoded by particular genes
Most common: modified strands of RNA/DNA that will bind with messenger RNA and prevent
them from producing their protein
Once molecules of mRNA are trapped, they are destroyed by enzymes
ANTISENSE: synthetic oligonucleotides contain sequences of bases complementary to those
contained by particular gene/molecule of mRNA
Chapter 6: VISION!






Sensory receptors
o Specialized neurons that detect particular category of physical events
o We receive information about the environment via them
o Do not confuse with receptors for neurotransmitters, neuromodulators and hormones
Sensory transduction
o Stimuli impinge on the receptors
o Alter their membrane potential
Receptor potential
o Slow, graded electrical potential produced by a receptor cell in response to a physical stimulus
o Affect the release of neurotransmitters
o Modify pattern of firing in neurons
o Information reaches the brain
Vision
o Sensory modality that receives most attention from experts
o Important for us as individual
o 20% of cerebral cortex role in analysis of visual info
The stimulus
o Our eye detect presence of light  see Electromagnetic Spectrum (figure 6.1 page 171)
o Wavelength of between 380nm and 760nm visible to us
o Animal have other wavelengths
 Honeybee: detect ultraviolet radiation
o Light
 Part of the continuum that we can see
 300 000 kilometers per second
o Perceptual dimensions of color
 Hue
 The dominant wavelength
 Visible spectrum displays range of hues that eye can detect
 Saturation
 Purity
 If all radiation of one wavelength, perceived color is pure or fully saturated
 Brightness
 Intensity
 If intensity of electromagnetic radiation increased, apparent brightness increased
 Color wavelength and saturation (figure 6.2 page 172)
 Intermediate amount of wavelengths = different mixture of wavelengths
 In figure: all same hue, but different levels of brightness and saturation
Anatomy of the visual system
o The eye  The Human Eye (Figure 6.4 page 173)












Orbits
 Bony pockets in front of the skull
 Eye suspended in orbits
Extraocular muscles
 6 of them in each eye
 Hold and move the orbits in place
Sclera
 Tough, white, outer coat of most of eye
 Opaque, does not permit entry of light
 PS: the cornea, transparent, admits light
Conjunctiva
 Can’t turn eyes and look at muscles behind eyeball because of them
 Hides the muscles
 Mucous membrane
 Line the eyelid and fold back to attach to the eye
 Thus, prevents a contact lens that has slipped off the cornea from falling behind the eye
Types of movements
 Vergence movements
o Cooperative movements
o Keep both eyes on same target
o Keep image on corresponding/identical parts of retinas
 Saccadic movements
o Shift gaze abruptly from one point to another
o Jerk movement in scanning a visual scene
 Pursuit movements
o Movement eye makes to maintain image of moving object on fovea
o Looking at finger while moving it around
Cornea
 Outer layer at front of eye
 Admits light
Pupil
 Regulated the amount of light that enters the eye
 Opening in iris
Iris
 Pigmented ring of muscles behind cornea
Lens
 Behind iris
 Series of transparent onionlike layers
Accommodation
 Changes in shape of the lens
 Due by contracting ciliary muscles
 To focus images of near or distant objects
Vitreous humor
 After passing the lens, light traverses this clear gelatinous substance
Retina
 Light falls on the retina after the vitreous humor
 Interior, posterior lining of the back of the eye
 Neural tissue and photoreceptive cells


o
o
o
o
Divided into 3 layers
o Photoreceptive layer
 Contains rods and cones
o Bipolar layer
 Middle layer of retina
 Convey info from photoreceptors to ganglion cells
o Ganglion cell layer
 Receives info from bipolar cells
 Axons give rise to optic nerve
o See Details of Retinal Circuitry Figure 6.6 page 175
Other neurons in retina
o Horizontal cells
 Interconnects adjacent photoreceptors and the outer processes of the
bipolar cells
o Amacrine cells
 Interconnects adjacent ganglion cells and inner processes of bipolar cells
Photoreceptors
 Transduce photic energy into electrical potential
 See chart that compares rods and cones Table 6.1 page 174
 Rods
 120 million
 Sensitive to light of low intensity
 Used in very dimly lighted environment
 Cones
 6 million
 Provide with most info about the environment
 Responsible for daytime vision, sharpness, acuity
 Maximum sensitivity of one of three different wavelengths of light
 Encoded color vision
 Outer segment
 Contains several hundred lamellae
 Connected by a cilium to inner segment
 Inner segment
 Contains nucleus
 Lamellae
 Thin plates of membrane
 Containing photopigments
 See Photoreceptors Figure 6.7 page 175
Fovea
 Central region of retina
 Mediates most acute vision
 Only cones
Optic disk
 Location of the exit point of fibers from ganglion cells
 Produces a blind spot because no receptors
 Where axons convey visual info gather together
 And leave eye through optic nerve
Transduction

o
Photopigments
 Special molecules embedded in membrane of lamellae
 Molecules consists of 2 parts
o Opsin
 A protein
 Many types of opsin
 Eg: Rhodopsin photopigment of human rods
o Retinal
 A lipid synthesized from vitamin A
 Rhodopsin
o When exposed to light, breaks into rod opsin and retinal
o Changes color from rosy to yellow: bleaches the photopigment
 Hyperpolarization
 Splitting of photopigment (into rod opsin and retinal) produces receptor potential
 Photoreceptor releases less neurotransmitter
 Depolarization
 Caused by reduction of neurotransmitter
 Causes bipolar cell to release more neurotransmitter
 Excites ganglion cells
 Must see Figure 6.8 page 176, this is a bit sketch and not well explained.
Connections between Eye and Brain
 1) Optic nerve
 2) Dorsal lateral geniculate nucleus (LGN) of the thalamus
 Contains 6 layers of neurons
 Each receives input from only 1 eye
 2 inner layers contains cells bodies that are larger that outer 4 layers
 Magnocellular layer
o 2 inner layers
o Perception of form, movements, depth, small differences in brightness to V1
 Parvocellular layers
o Outer 4 later
o Perception of color, fine details to V1
 Koniocellular sublayer
o One of the sublayers of neurons on LGN
o Ventral to each of magnocellular and parvocellular layers
o Transmit info from short-wavelength(blue) cones to V1
 3) Optic nerves
 4) Optic chiasm
 Where optic nerves of NASAL sides of the retina join at base of the brain
 Form a X shape and ascend opposite side of brain
 Optic nerves from TEMPORAL sides remain on same side of brain, thus, do not form a
X
 5) Optic radiations
 6) Striate cortex
 Primary visual cortex
 Each hemisphere receives info from contralateral visual scene
 NOT correct to say that each hemisphere receives info from contralateral EYE
 See Primary Visual Pathway Figure 6.11 page 178

Coding of visual information in the retina
o Coding of light and dark
 Receptive field of a neuron
 Part of visual field that an individual neuron can “see”
 Place which stimuli must be located to produce response of neuron
 Depends on location of photoreceptors on retina
 Consist of a circular center surrounded by a ring
 Types of ganglion cells
 ON cells
o Respond with excitatory burst when retina illuminated
o When light fell on the central field
o Inhibited when light fell on surrounding field
 OFF cells
o Respond when light was turned off (center)
o Inhibited when light fell on surrounding field
 ON/OFF cells
o Respond briefly when light was turned on than off
 See Figure 6.13 page 180
o Coding of color
 Trichromatic theory by Thomas Young
 Human eye can see any color produced by mixing 3 colors
 Color mixing
 Refers to addition of 2 or more light sources
 Shine beam of red light with beam of green light on white screen = yellow light
 Pigment mixing
 Combine yellow and blue pigments (eg: paint) = green pigments
 Opponent colors
 Red vs. green
 Yellow vs. blue
 Cannot imagine reddish green or bluish yellow
 Primary colors
 Yellow, blue, red and green
 That do not appear to be blends of others
 Colorless
 Black and white
o Photoreceptors: Trichromatic coding
 3 different type of photoreceptors (cones) responsible for color vision
 S: 420 nm (blue-violet)
 M: 530nm (green)
 L: 560nm (yellow-green)
 Genetic defects
 Results from anomalies to one or more cones
 Protanopia (1st color defect)
o Gene X chromosomes  more men at risk
o Confuse red and green, they seem like yellow
o See world in blue and yellow
o Visual acuity normal
o Their red cones are filled with green cone opsin


Deuteranopia (2nd color defect)
o On X chromosome again
o Also confuse red and green
o Also have ok acuity
o Green cones are filled with red cone opsin
o Dichromatic vision
 Tritanopia (3rd color defect)
o NOT located on X chromosome  equal risk for males and females
o Difficulty with hue of short-wavelengths
o See world of greens and reds
o Clear blue sky = bright green
o Yellow = pink
o Retinas lack blue cones
o Does not noticeably affect acuity
o Retinal ganglion cells: opponent-process coding
 2 kinds of color-sensitive ganglion
 Red-green
 Yellow-blue
 Center-surround receptive field
 Yellow on, blue off vs. blue on, yellow off
 Red on, green off vs. green on, red off
 An axon that signals red or green (or blue or yellow) can either increase or decrease its
rate of firing, but not both  cannot have reddish green (or bluish yellow)
 Very detailed Figure 6.19 page 184
o Adaptation: negative afterimages
 Negative afterimages
 Image seen after a portion of the retina is exposed to an intense visual stimulus
 Consists of colors complementary to those of the physical stimulus
 Complementary colors
 Colors that make white or gray when mixed together
 Cause
 Adaptation in the rate of firing of retinal ganglion cells
 When ganglion cells are excited/inhibited for a long time
 Show rebound effect  firing faster/slower than usual
 Eg: Look at green for a long time, inhibiting some red-green ganglion cells. When look at
white page right after, the red-green ganglion cell will fire faster than normal. Thus, we
see a red afterimage.
Analysis of visual information: role of the striate cortex
o Anatomy of the striate cortex
 6 layers
 Map of contralateral half of visual field
 Map is distorted
 25% of striate cortex devoted to info from fovea which is tiny
 Neurons not simply respond to spot of light
 They selectively respond to specific features of the visual world
o Orientation and movement
 Cell will only respond if line is in particular orientation and position
 Some respond best to vertical line, others horizontal lines


Simple cells
 Orientation-sensitive neuron
 Receptive field organized in a opponent fashion
 Complex cells
 Respond to presence of line segment with particular orientation
 Especially when line moves perpendicularly to its orientation
 Hypercomplex cells
 Lines with particular orientation that ends at a particular point
o Spatial frequency
 Sine-wave grating
 Straight parallel bands varying continuously in brightness according to sine-wave
function
 Along a line perpendicular to their lengths
 Spatial frequency of sine-wave grating = variation in brightness measured in cycles per
degree of visual field
 When image where low special frequency is removed  very difficult to perceive
 See Figures 6.25 and 6.27 page 188 and 189 for nice pictures
o Retinal disparity
 Monocular vision ( 1 eye)
 Binocular vision (2 eyes)
 Stereoscopic vision
 Perception of depth through process of stereopsis
 Very important in visual guidance of fine movements of hands and fingers
 Neurons in striate cortex
 Most binocular
 Respond to visual stimulation of either eye
 Most receive info from magnocellular system
 Contribute in perception of depth
 Retinal disparity
 Points on objects located at different distances from observer will fall on slightly
different locations on 2 retinas
 Basis for stereopsis
 Stereopsis
 Each eye sees a different 3D scene slightly different
 Retinal disparity indicated differences in the distance of objects from the observer
o Color
 From color-sensitive ganglion cells, to LGN (through parvocellular and koniocellular layers)
 To cytochrome oxidase (CO) blobs
 Central region of a module of V1
 Revealed by stain for cytochrome oxidase
 Contains wavelength-sensitive neurons
 Part of parvocellular system
o Modular organization of the striate cortex
 Ocular dominance
 A particular neuron receives input from one eye than from the other
Analysis of visual information: role of the visual association cortex
o Info from striate cortex analyzed in visual association cortex
o Neurons in striate cortex send axons to extrastriate cortex
o


Extrastriate cortex
 Region of visual association cortex
 Receives fibers from the striate cortex and superior colliculi
 Projects to inferior temporal cortex
 Primate extrastriate cortex
 Consists of several regions
 Each contains one or more independent maps of visual field
 Each region is specialized, neurons that respond to particular features of visual info
(orientation, movement, special frequency, retinal disparity, color)
o Results of functional-imaging study by Murray
 Pathway that travel up the hierarchy
 From regions of visual association cortex back to striate cortex
 As you go from V1 to V2 to V3… the neurons code more elements of more complex stimuli,
such as corners
o 2 streams of visual analysis
 Dorsal stream
 From striate cortex to posterior parietal cortex
 Axons from V1 directly to V5, a region of the extrastriate cortex devoted to analysis of
movement
 Recognizes where the object is located, its speed and direction
 Ventral stream
 From striate cortex to inferior temporal cortex
 Recognizes what an object is and what color it has
 See Figure 6.34 page 194
Perception of color
o Studies with laboratory animals
 Striate cortex send color-related info to V2
 Neurons in V2 send info to V4
 V4 has color-sensitive neurons, as well as forms
 TEO
 Region of monkey
 Portion of inferior temporal cortex just anterior to V4
 Plays critical role in visual discrimination
 When V4 is intact and TEO is destroyedimpairment in color discrimination
o Color consistency
 Relatively constant appearance of the colors of an object viewed under varying lighting
conditions
o Studies with humans
 Cerebral achromatopsia
 Vision without color
 Lesions oh extrastriate cortex
 No disruption of acuity
 Cannot even imagine colors or remember color of objects they saw before damage
 If damage is unilateral  loss of color vision in ½ of visual field
Perception of form
o Studies with animals
 Recognition of visual pattern and identification takes place in inferior temporal cortex
 At the end of ventral stream is where form and color are put together
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TEO (posterior inferior temporal cortex) and TE (anterior inferior temporal cortex) important for
visual discrimination
 V1 = analysis of elementary aspects of information, very small visual field
 Successive regions analyze more complex characteristics
 Size of receptive fields grows as the hierarchy is ascended
 Receptive fields of neurons in TEO are larger than the ones in V4
 Neurons in TE are the largest of all
o Studies with humans
 Visual agnosia
 Failure to know
 Damage to visual association cortex that contribute to the ventral stream
 Inability to visually perceive or identify a stimulus
 Normal intellectual capacity
 No blindness
 Prosopagnosia
 Symptom of visual agnosia
 Inability to recognize particular faces
 Recognize that they are looking at a face, but don’t know who’s
 Fusiform face area (FFA)
 In the ventral stream, in the fusiform gyrus on temporal lobe
 Where special face-recognizing circuits are
 Extrastriate body area (EBA)
 In ventral stream, posterior to FFA, in lateral occipitotemporal cortex
 Perception of human body and body parts other than faces
 Parahippocampal place area (PPA)
 Region of limbic cortex on ventromedial temporal lobe
 Perception of places, scenes
Perception of movement
o Studies with animals
 V5 or MT (medial temporal) has neurons that respond to movement
 Receives input from striate cortex
 Axons that transmit information from magnocellular system are thick and heavily myelinated
 So that we perceive movements accurately and quickly (survival)
 Also input from superior colliculus
 Involves in visual reflexes
 Movement sensitivity of neurons in area V5
 Optic flow
 Complex motion of points
 Caused by relative movement between observer and environment
 Provides info about relative distance of objects from observer
 And relative direction of movement
 Optic flow analyzed by dorsolateral medial superior temporal cortex (MST) that receives
info from V5 and makes further analysis
o Studies with humans
 Akinetopsia
 Bilateral damage in human brain that includes area V5
 Inability to perceive movement
 Optic flow
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 MT/MST respond to optic flow
Perception of spatial location
o Involves parietal lobe
 Spatial, somatosensory perception, visual, auditory, somatosensory and vertibular information
 Perform tasks
 Damage there disrupts performance of variety of tasks that require perceiving and remembering
location of objects
o Intraparietal sulcus (IPS)
 The end of dorsal stream of visual association cortex
 Involved in perception of location, visual attention and control of eye and hand movements
 5 regions in this sulcus are of interest
 AIP (anterior)
o Grasping and manipulating hand movements
 LIP (lateral) and VIP (ventral)
o Visual attention and control of saccadic eye movements
 CIP (caudal)
o Perception of depth from stereopsis
 MIP (medial) and VIP (ventral)
o Visual control of reaching and pointing
 See Figure 6.47 page 206 for anatomy of these regions
See Table 6.3 page 208 and 209 for a summary of important visual parts
Audition
The Stimulus
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Sounds are produced by objects that vibrate and set molecules of air into motion.
The waves produced by the vibration of an object travel at approximately 700 miles per hour.
If the vibration ranges between 30 and 20 00 times per second they are perceived as sounds.
Changes in air pressure from sound waves move the eardrum in and out. Air molecules are closer
together in regions of higher pressure and farther apart in regions of lower pressure.
Sounds have three different perceptual dimensions: pitch, loudness, and timbre.
Pitch: Corresponds to the fundamental frequency of sound (vibration). It is measured in Hz (cycles per
second).
Loudness: Is a function of intensity. The more vigorous the vibrations of an object, the louder the sound
perceived.
Timbre: Provides information about the nature of the particular sound. It corresponds to the complexity
dimension of the sound.
The ear is an analytical organ. When two different frequencies of sound waves are mixed, we do not
perceive and intermediate tone; instead, we hear both original tones.
Anatomy of the Ear
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Sound is funneled via the pinna (external ear) through the ear canal to the tympanic membrane
(eardrum), which vibrates with the sound.
The middle ear consists of a hollow region behind the tympanic membrane. It contains the bones of the
middle ear called the ossicles, which are set into vibration by the tympanic membrane. The three ossicles
bones are: malleus, incus, and stapes.
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The malleus (hammer) connects with the tympanic membrane and transmits vibrations via the incus
(anvil) and stapes (stirrup) to the cochlea, the structure that contains the receptors.
The baseplate of the stapes presses against the membrane behind the oval window. It is an opening in
the bone surrounding the cochlea that reveals a membrane, against which the baseplate of the stapes
presses, transmitting sound vibrations into the fluid within the cochlea.
The cochlea is a snail-shaped structure of the inner ear that contains the auditory transducing
mechanisms. It is filled with fluid; therefore, sounds transmitted through the air must be transferred into
a liquid medium. The chain of ossicles serves as an extremely efficient means of energy transmission.
The bones provide a mechanical advantage, with the baseplate of the stapes making smaller but more
forceful excursions against the oval window than the tympanic membrane makes against the malleus.
The cochlea is divided longitudinally in three sections: the scala vestibuli (“vestibular stairway); scala
media (“middle stairway”); and scala tympani (tympanic stairway”)
The receptive organ, known as the organ of Coti, is located on the basilar membrane that contains the
auditory hair cells. It consists of the basilar membrane, the hair cells, and the tectorial membrane.
Hair cells: The receptive cell of the auditory apparatus that are anchored via rodlike Deiter’s cells, to
the basilar membrane.
Deiter’s cell: A supporting cell that sustain the auditory hair cells.
Tectorial membrane: A membrane located above the basilar membrane; serves as a shelf against which
the cilia of the auditory hair cells move.
Sound waves cause the basilar membrane to move relative to the tectorial membrane, which bends to the
cilia of the hair cells. This bending produces receptor potentials.
George von Bekesy found that vibratory energy exerted on the oval window causes the basilar
membrane to bend. High-frequency sounds cause the end nearest oval window to bend.
Round window: An opening in the bone surrounding the cochlea of the inner ear that permits vibrations
to be transmitted, via the oval window, into the fluid in the cochlea.
When the stapes pushes against the membrane behind the oval window, the membrane behind the round
window bulges outward. Different high-frequency and medium-frequency sound vibrations cause
flexing of different portions of the basilar membrane. In contrast, low-frequency sound vibrations cause
the tip of the basilar membrane to flex in synchrony with the vibrations.
Some people suffer from a middle ear disorder disease that causes the bone to grow over the round
window and suffer a severe hearing loss. This can be fixed by fensestration (“window making”) a
surgical procedure.
Auditory Hair Cells and the Transduction of Auditory Information
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Two types of auditory receptors: inner and outer auditory hair cells, located on the basilar membrane.
Cilia: Fine hair-like appendages found on hair cells, arranged in rows according to height. They are
involved in movement or in transducing sensory information; found on the receptors in the auditory and
vestibular system. The human cochlea contains around 3500 inner hair cells and 12 000 outer cells.
The hair cell form synapses with dendrites of bipolar neurons whose axons bring auditory information
to the brain.
Sound waves cause both the basilar membranes and the tectorial membrane to flex up and down. These
movements bend the cilia of the hair cells in one direction or other.
Cilia contain a core of actin filaments surrounded by myosin filaments and these proteins make the cilia
stiff and rigid.
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Tip link: An elastic filament that attaches the tip of one cilium to the side of the adjacent cilium.
Normally they are under a small amount of tension
Insertional Plaque: The point of attachment of a tip link to a cilium. Here is where receptor potentials
are triggered.
The movement of the bundle of cilia toward the tallest one increases the firing rate of the cochlear nerve
axon attached to hair cell, while movement away from the tallest one decreases it.
The movement toward the tallest cilium increases tension on the tip links, which opens the ion channel
and increases the influx of K+ and Ca2+ ions. The movement toward the shortest cilium removes tension
from the tip links, which permits the ion channels to close, stopping the influx of cations.
The Auditory Pathway
Connections with the Cochlear Nerve
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The organ of Corti sends auditory information to the brain by means of the cochlear nerve, a branch of
the auditory nerve.
The neurons that give rise to the afferent axons that travel through this nerve are of the bipolar type.
These neurons have axonal processes, capable of sustaining action potentials that protrude from both
ends of the soma.
The end of one process acts like a dendrite, responding with excitatory postsynaptic potentials when the
neurotransmitter is released by the auditory hairy cells. The excitatory postsynaptic potentials trigger
action potentials in the auditory nerve axons, which form synapses with neurons in the medulla.
Each cochlear nerve contains approximately 50,000 afferent axons. The dendrites of approximately 95%
of these axons form synapses with the inner hair cells, the remaining 5% form synapses with the much
more outer hair cells.
The connections between these axons and auditory nerves suggest that they are of primary importance in
the transmission of auditory information to the central nervous system (CNS).
The inner hair cells are necessary for normal hearing.
The outer hair cells are effector cells involved in altering the mechanical characteristics of the basilar
membrane and thus influencing the effects of sound vibrations on the inner hair cells.
The cochlear nerves contain efferent axons as well as afferent ones.
Olivocochlear Bundle: A bundle of efferent axons that travel from the olivary complex of the medulla
to the auditory hair cells on cochlea.
The neurotransmitter at the afferent synapses is glutamate. The efferent terminal buttons secrete
acetylcholine, which has an inhibitory effect on the hair cells.
The Central Auditory System
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Axons enter the cochlear nucleus of the medulla and synapse there. Cochlear nucleus: a group of
nuclei located in the medulla that receive auditory information from the cochlea.
Most of the neurons in the cochlear nucleus send axons to the superior olivary complex. Superior
Olivary Complex: A group of nuclei in the medulla; involved with auditory functions, including
localization of the source of sound.
Axons of neurons in these nuclei pass through a large fiber bundle called the lateral lemniscus. Lateral
Lemnsicus: A band of fibers running rostrally through the medulla and pons; carries fibers of the
auditory system.
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Auditory information and reticular formation are relayed to the cerebellum.
The basal end of the basilar membrane ( the end toward the oval window) is represented most medially
in the auditory cortex, and the apical end is represented most laterally there.
Tonotopic Representation: A topographically organized mapping of different frequencies of sound that
are represented in a particular region of the brain.
The auditory cortex seems to be arranged in a hierarchy. The primary auditory cortex lies hidden on the
upper bank of the lateral fissure.
Core region: Contains the primary auditory cortex, located on a gyrus on the dorsal surface on the
temporal lobe.
Belt region: First level of auditory association cortex that surrounds the primary auditory cortex.
Parabelt region: The highest level of auditory association cortex, surrounds the belt region.
The auditory cortex is arranged in two streams: dorsal and ventral. The dorsal stream is involved with
sound localization and the ventral is involved with analysis of complex sounds.
Perception of Pitch
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Stimuli of different frequencies maximally deform different regions of the basilar membrane. Higher
frequencies produce more displacement at the basal end of the membrane.
Place Code: The system by which information about different frequencies is coded by different
locations on the basilar membrane.
A code represents a means by which neurons can represent information.
High doses of the antibiotic drugs kanamycin and neomycin produce degeneration of the auditory hair
cells.
Good evidence for place coding of pitch comes from the effectiveness of cochlear implants.
Cochlear implants: An electronic device surgically implanted in the inner ear that are used to restore
hearing in people with deafness caused by the damage in hair cells. It consists of a microphone and a
miniaturized electronic signal processor. Its main goal is to restore a person’s ability to understand
speech. They are most effective in very young children.
It appears that the point of maximum vibration of the basilar membrane to a particular frequency is very
precisely localized, but only when the cells in the organ of Corti are alive and healthy.
When the basilar membrane vibrates, movement of the cilia of the outer hair cells opens and closes ion
channels, causing changes in the membrane potential. These changes cause movements of the contractile
proteins, thus lengthening and shortening the cells. These changes in length amplify the vibrations of the
basilar membrane. As a consequence, the signal that is received by inner hair cells is enhanced, which
greatly increase the sensitivity of the inner ear to sound waves.
Rate Coding
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It appears that lower frequencies are detected by neurons that fire in synchrony to the movements of the
apical end of the basilar membrane.
Rate Coding: the system by which information about different frequencies is coded by the rate of firing
of neurons in the auditory system.
Perception of Loudness
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Wilska (1935) found that subjects could detect a sound even when the eardrum was vibrated over a
distance less than the diameter of a hydrogen atom, showing that the auditory system is very sensitive.
The axons of the cochlear nerve appear to inform the brain of the loudness of a stimulus by altering their
rate of firing.
Louder sounds produce more intense vibrations of the eardrum and ossicles, which produce more
intense shearing force on the cilia of the auditory hair cells.
Most investigators believe that the loudness of low-frequency sounds is signaled by the number of axons
arising from the neurons in the apex of the basilar, that are active at a given time.
Perception of Timbre
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We hear sounds of with a rich mixture of frequencies--- sounds of complex timbre.
Fundamental frequency: The lowest, and usually most intense, frequency of a complex sound; most
often perceived as the sound’s basic pitch.
Overtone: The frequency of complex tones that occurs at multiples of the fundamental frequency.
Perception of Spatial Location
Localization by Means of Arrival Time and Phase Differences
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Neurons in our auditory system respond selectively to different arrival times of the sound waves at the
left and right ears.
Some neurons, such as those in the superior olivary complex of the medulla, respond according to the
difference in arrival times of sound waves produced by clicks presented binaurally ( both ears).
Phase differences: The difference in arrival times of the sound waves at each of the eardrums.
Jeffres ( 1948) suggested that neurons received information from two sets of axons coming from the two
ears. Each neuron served as a coincidence detector, it responded only if it received signals
simultaneously from synapses belonging to both sets of axons.
Localization by Means of Intensity Differences
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High frequency stimuli that occur to the right or left of the midline stimulate the ears unequally.
The ear closest to the source of the sound receives the most intense stimulation.
Localization by Means of Timbre
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How can we determine the elevation of the source of a sound and perceive whether it is in front or
behind us?
o We can turn and tilt our heads, transforming the discrimination into a left-right decision.
o Analysis of timbre: Depending on the angle at which the sound waves strike the folds and ridges
of the external ear (pinna), different frequencies will be enhanced or attenuated.
Sounds coming from behind the head will sound different from those coming from above the head or in
front of it, and sounds coming from above will sound different from those coming from the level of our
ears.
The first level of analysis of information about the elevation of a sound appears to take place in the
dorsal cochlear nucleus.
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People’s ears differ in shape; thus, the changes in the timbre of a sound coming from different locations
will also differ from person to person.
Zwiers, Van Opstal, and Crusynberg (2001) found that blind people had more difficulty judging the
elevation of sounds than sighted people did, especially if some noise was present.
Perceptions of Complex Sounds
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Hearing has three primary functions: to detect sounds, to determine the location of their sources, and to
recognize and identify of these sources-and thus their meaning and relevance to us.
Perception of Environmental Sounds and Their Location
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Pattern recognition: The task of the auditory system in identifying sound sources.
The auditory system must recognize that particular patterns of constantly changing activity belong to
different sound sources.
Perception of complex sounds appears to be accomplished by circuits of neurons in the auditory cortex.
Recognition of complex sounds requires that the timing of changes in the components of the sounds be
preserved all the way to the auditory cortex.
The neurons that convey information to the auditory cortex contain special features that permit them to
conduct this information rapidly and accurately.
The terminal buttons form synapses with the somatic membrane of the postsynaptic neurons, which
minimizes the distance between the synapses and the axon--- and the delay in conducting information to
the axon of the postsynaptic neuron.
Humans and monkeys can use the convergence of sight and sound to recognize which of several objects
in the environment is making a noise.
We can learn the association between the sight of an object and the sound it makes.
Lesions of the auditory association cortex can produce auditory agnosias--- impairment of various
aspects of auditory perception, even though the individuals are not deaf.
Different regions of the auditory cortex are involved in perceiving what and where.
Perception of the identity of sounds activated the ventral stream of the auditory cortex and perception of
the location of sounds activated the dorsal stream.
Perception of Music
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Music consists of sounds of various pitches and timbres played in a particular sequence with an
underlying rhythm.
A melody is recognized by the relative intervals between its notes, not by their absolute value.
Musical perception requires recognition of sequences of notes, their adherence to rules that govern
permissible pitches, harmonic combination of notes, and rhythmical structure.
Musical perception involves a substantial memory capacity.
The analysis of music in the brain begins with the subcortical auditory pathways and the primary
auditory cortex.
Pitch is determined by the fundamental frequency, and timbre is determined by the mixture of overtones.
Different regions of the brain are involved in different aspects of musical perception:
o Inferior Frontal Cortex Harmony
o Left Auditory Cortex Rhythmic Patterns
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o The Cerebellum and Ganglia Timing of Musical Rhythm
Some of the effects of musical training can be seen in changes in the structure or activity of portions of
the auditory system of the brain.
Approximately 4% of the population exhibits congenital amusia—a severe and persistent deficit in
musical ability (but not in perception of speech or environmental sounds)—that becomes apparent early
in life. It appears to have a genetic basis.
Vestibular System
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Two components: The vestibular sacs and the semicircular canals. They represent the second and third
component of the labyrinths of the inner ear.
Vestibular sacs: Respond to the force of gravity and inform the brain about the brain about the head’s
orientation. It detects the changes in the tilt of the head.
Semicircular canal: Respond to angular acceleration—changes in the rotation of the head.
Functions of the vestibular system:
o Balance
o Maintenance of the head in an upright position
o Adjustment of the of eye movement to compensate for head movements
Certain low frequency stimulation of the vestibular sacs can produce nausea.
Stimulation of the semicircular canals can produce dizziness and rhythmic eye movements (nystagmus)
Anatomy of the Vestibular Apparatus
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Two vestibular sacs: Utricle (“little punch”) and Saccule ( “ little sack”)
Ampulla: An enlargement in a semicircular canal that contains the organ in which the sensory receptors
reside.
Cupula: A gelatinous mass found in the ampulla of the semicircular canals; moves in response to the
flow of the fluid in the canals.
Angular acceleration is thus translated into bending of the cupula, which exerts a shearing force on the
cilia of the hair cells.
The vestibular sacs are roughly circular, and each contains a patch of receptive tissue.
The receptive tissue is located on the “floor” of the utricle and on the “wall” of the saccule when the
head is in an upright position.
Otoconia: Small crystals of calcium carbonate found in the gelatinous mass that contains the cilia of the
hair cells.
The weight of the otoconia in the gelatinous mass shifts when the head tilts, causing a shearing force on
the some of the cilia of the hair cells.
The Receptor Cells
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The hair cells of the vestibular sacs contain several cilia ( a long one and several shorter ones). A
shearing force of the cilia opens ion channels, and the entry of potassium ions depolarizes the ciliary
membrane.
The Vestibular Pathway
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The vestibular and cochlear nerves constitute the two branches of the eight cranial nerve (auditory
nerve)
Vestibular ganglion: A nodule on the vestibular nerve that contains the cell bodies of the bipolar
neurons that convey vestibular information to the brain.
Most of the axons of the vestibular nerve synapse within the vestibular nuclei in the medulla, but some
axons travel directly to the cerebellum.
Vestibular information is received by the vestibular nuclei in the medulla, which relay it on the
cerebellum, spinal cord, medulla, pons, and temporal cortex. These pathways are responsible for control
of posture, head movements, and eye movements.
Vestibulo-ocular reflex: The vestibular system exerts direct control on eye movement to compensate for
the sudden head movements.
Somatosenses
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They provide information about what is happening on the surface of our body and inside it.
Cutaneous Senses: One of the somatosenses; include sensitivity to smituli that involves the skin.
Proprioception: Perception of the body’s position and posture.
Kinesthesia: Perception of the body’s own movements.
Organic Sense: A sense modality that arises from receptors located within the inner organs of the body.
The Stimuli
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The cutaneous senses respond to several different types of stimuli:
o Pressure
o Vibration
o Heating
o Cooling
o Events that cause tissue damage
We use vibration stimuli to judge an object’s roughness
Kinesthesia is provided by stretch receptors in skeletal muscles that report changes in muscle length to
the central nervous system and by stretch receptors in tendons that measure the force being exerted by
the muscles.
Anatomy of the Skin and Its Receptive Organs
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Skin consists of subcutaneous tissue, dermis, and epidermis and contains various receptors scattered
these layers.
Glabrous Skin: Hairless skin, found on the fingertips and palms and on the bottoms of our toes and
feet.
Ruffini corpuscle: A vibration sensitive organ located in the hairy skin that responds to indentation of
the skin.
Pacinian corpuscle: A specialized, encapsulated somatosentory nerve ending that detects mechanical
stimuli; especially vibrations.
Free nerve endings, which detect painful stimuli and changes in temperature, are found just below
surface of the skin.
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Nerve endings that detect the movement of hair are found in the basketwork around the base of hair
follicles.
Meissner’s couple: The touch-sensitive end organs located in the papillae (“nipples”), small elevations
of the dermis that project up into the epidermis.
Merkel’s disk: The touch-sensitive end organs found at the base of the epidermis, adjacent to sweat
ducts. They respond to the indentation of the skin.
Mechanoreceptors: Receptors that respond to mechanical stimulation.
Perception of Cutaneous Stimulation
Touch
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Sensitivity to pressure and vibration is caused by movement of the skins, which moves the dendrites of
mechanoreceptors.
When the dendrites of the mechanoreceptors bend, ion channels open, producing a receptor potential.
Most information about tactile sensation is precisely localized-that is, we perceive the location on our
skin where we are being touched.
Investigators concluded that small diameter unmyelinated axons constitute a system for limbic touch,
hormonal and affiliative responses to caresslike, skin-to-skin contact between individuals.
Our cutaneous senses are used much more often to analyze shapes and textures of stimulus objects that
are moving with respect to the surface of the skin.
Studies of people who make especially precise use of their fingertips show changes in the regions of
somatosensory cortex that receive information from this part of the body.
Tactile experience, such as gained by musicians, increases the portion of the somatosensory cortex
devoted to the fingers involved in this experience.
Temperature
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Increases in temperature lower the sensitivity of warmth receptors and raise the sensitivity of cold
receptors.
Moderate changes in skin temperature are soon perceived as neutral, and deviations above or below this
temperature are perceived as warmth of coolness.
There are two categories of thermal receptors: those that respond to warmth and those that respond to
coolness.
Transduction of different ranges of temperatures is accomplished by six members of the TRP (transient
receptor potential) family of receptors.
One of the coolness receptors, TRPM8, also responds to menthol and is involved in responsiveness to
environmental cold.
Pain
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Stimuli that produce pain also tend to trigger species-typical escape and withdrawal responses.
There appear to be at least three types of pain receptor (nociceptors or “detectors of noxious stimuli”):
o High-threshold mechanoreceptors: Free nerve endings that respond to intense pressure.
o Fibers with capsaicin receptors (TRPV1): Detect extremes of heat, acid and the presence of
capsain ( the active ingredient in chili peppers)
o Fibers with TRPA1: Sensitive to chemical irritants and inflammation. It provides information
about the presence of chemicals that produce inflammation.
Itch
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It is caused by skin irritation.
“It is an unpleasant sensation that elicits the desire or reflex to scratch”
Scratching reduces itching because pain suppresses itching.
Histamine and other chemical released by skin irritation and allergic reactions are important sources of
itching.
At least two different types of neurons transmit itch-related information to the CNS.
The Somatosensory Pathways
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Somatoesensory axons from the skin, muscles, or internal organs enter the central nervous system via
spinal nerves.
Precisely localized information (such as fine touch) and imprecisely localized information (such as pain
and temperature) are transmitted by different pathways. The first ascend through the dorsal columns in
the white matter of the spinal cord to nuclei in the lower medulla; the latter cross to the other side of the
spinal cord and ascend through the spinolathamic tract to the ventral posterior nuclei of the thalamus.
Organic sensibility reaches the central nervous system by means of axons that travel through nerves of
the autonomic nervous system.
The neurons in the primary somatosensory cortex are topographically arranged, according to the part of
the body from which they receive sensory information (somatotopic representation).
Damage to the somatosensory association cortex can cause tactile agnosia, inability to recognize
common objects by means of touch.
Perception of Pain
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Pain serves as a constructive role.
A particular voltage-dependant sodium channel, Nax 1.7, plays an essential role in pain sensation.
Mutations of the gene for this protein produce total insensitivity to pain.
Some environmental events diminish the perception of pain.
Pain perception is a complex phenomenon with sensory and emotional components that can be modified
by experience and the immediate environment.
Pain appears to have three different perceptual and behavioral effects:
o Sensory component: Pure perception of the intensity of a painful stimulus.
o Immediate emotional consequence of pain: Unpleasantness or degree to which the individual is
bothered by the painful stimulus.
o Long-term emotional implications of chronic pain: The threat that such pain represents to one’s
future comfort and well-being.
The sensory component is mediated by the primary and secondary and somatosensory cortex; the
immediate emotional component appears to be mediated by the anterior cingulate cortex and the insular
cortex; and the long-term emotional context appears to be mediated by the prefrontal cortex.
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Functional-imaging studies using hypnotic suggestion found that a decrease in the sensory component of
pain reduced activation of theof the somatosensory cortex and that reduction of the unpleasantness of
pain reduced the activation of the anterior cingulate cortex.
The phantom limb phenomenon, which often is accompanied by phantom pain, appears to be inherent in
the organization of the parietal lobe. An explanation to this phenomena is related to the activity of the
sensory axons belonging to the amputated limb.
Endogenous Modification of Pain Sensitivity
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Investigators have known that perception of pain can be modified by environmental stimuli.
Recently, it has been revealed the existence of neural circuits whose activity can produce analgesia
(reduce pain).
Electrical stimulation of particular locations within the brain can cause analgesia (e.g. the periaqueductal
gray and in the rostroventral medulla).
Analgesic brain stimulation apparently triggers the neural mechanisms that reduce pain, primarily by
causing endogenous opioids to be released.
Connections from the periaqueductal gray matter to the nucleus raphe magnus of the medulla activate
serotogenic neurons located there. These neurons send axons to the dorsal horn of the spinal cord gray
matter, where they inhibit the transmission of pain to the brain.
Nucleus raphe magnus: A nucleus of the raphe that contains serotonin-secreting neurons that project to
the dorsal gray matter of the spinal cord and is involved in analgesia produced by opiates.
In humans, chronic pain is sometimes treated by implanting electrodes in the periaqueductal gray matter
or the thalamus and permitting patients to stimulate the brain through these electrodes when the pain
becomes severe.
Pain sensitivity can be regulated by direct neural connections, as well as by the secretion of endogenous
opioids.
Biological Significance of Analgesia
 Analgesia occurs when it is important for an animal to continue a behavior that would tend to be
inhibited by pain (e.g. mating or fishing).
 The administration of a placebo can also produce analgesia. Because this effect is blocked by naloxone,
it must involve the release of endogenous opioids.
 Functional-imaging studies suggest that the placebo effect may be caused by increased activity of the
prefrontal cortex, which activates the periaqueductal gray matter and inhibits the activity of the anterior
cingulate cortex and insular cortex, inducing analgesia.
 Learning to increase or decrease the activity of one’s own anterior cingulate cortex using feedback from
fMRI increases or decreases a person’s sensitivity to pain.
Gustation
The Stimuli
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For a substance to be tasted, molecules of it must dissolve in the saliva and stimulate the taste receptors
on the tongue.
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Five qualities of taste:
o Bitterness
o Sourness
o Sweetness
o Saltiness
o Umami
Flavor is a composite of olfaction and gestation.
Umami (“good taste”): The taste sensation produced by glutamate, a substance used as a flavor
enhancer in Asian cuisine.
Most species of animals will readily ingest substances that taste sweet or somewhat salty. On the other
hand, they will tend to avoid substances that taste sour or bitter.
Bitter foods often contain alkaloids, many of which are poisonous. Also, sour foods have usually
undergone bacterial fermentation, which can produce toxins.
Sweet foods (fruits) are nutritious and salty foods contain an important cation: sodium.
Anatomy of the Taste Buds and the Gustatory Cells
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The tongue, palate, pharynx, and larynx contain approximately 10 000 taste buds. Most of them are
arranged around papillae.
Taste receptor cells form synapses with dendrites of bipolar neurons whose axons convey gustatory
information to the brain through the seventh, ninth and tenth cranial nerves.
The receptor cells have a life span of ten days.
Perception of Gustatory Information
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The tasted molecule binds with the receptor and produces changes in membrane permeability that cause
receptor potentials.
Saltiness receptors appear to be simple sodium channels. When present in the saliva, sodium enters the
taste cell and depolarizes it, triggering action potentials that cause the cell to release neurotransmitter.
Sourness receptors appear to be simple sodium channels.
Sourness receptors appear to detect the presence of hydrogen ions, which activate a transient receptor
potential ion channel known as PKD2L1.
Bitter, sweet, and umami tastes are detected by two families of receptors: sweetness by a receptor
consisting of T1R2+T1R3, umami by one consisting of T1R1+T1R3, and bitterness by thirty different
members of the T2R family.
A fatty acid transporter, CD36, found in the papillae of the tongue, detects molecules of fatty acids
produced when and enzyme, lingual lipase, break downs some molecules of fat in the mouth.
The Gustatory Pathway
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Chorda Tympani: A branch of the facial nerve that passes beneath the eardrum; conveys taste
information from the anterior part of the tongue and controls the secretion of some salivary glands.
Nucleus of the solitary tract: First relay station for taste. It is a nucleus of the medulla that receives
information from visceral organs and from the gustatory system.
Different tastes activate different regions of the primary gustatory cortex.
The caudolateral orbifrontal cortex contains the secondary gustatory cortex.
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Gustatory information is also sent to the amygdale, hypothalamus, and basal forebrain.
Olfaction
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It is the second chemical sense, and helps us to identify food and avoid food that has spoiled and is unfit
to eat.
The olfactory system is second only to the visual system in the number of sensory cell, with an
estimated 10 million cells.
Stimulus
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The stimulus for odor consists of volatile substances having a molecular weight in the range of approx.
15 to 300.
Anatomy of the Olfactory Apparatus
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Olfactory epithelium: Home of our 6 million olfactory reception cells. It us a tissue that covers the
cibriform plate; contains the cilia of the olfactory receptors. It is located at the top of the nasal cavity.
Olfactory receptor cells are bipolar neurons whose cell bodies lie within the olfactory mucosa that lines
the cibriform plate, a bone at the base of the rostral part of the brain.
Constant production of olfactory receptors cell, that live longer than the gustatory receptor cells.
The receptor sends processes toward the surface of the mucosa, which divide into cilia. The membranes
of these cilia contain receptors that detect aromatic molecules dissolved in the air that sweeps past the
olfactory mucosa.
Olfactory Bulbs: The protrusion at the end of the olfactory tract; receives input from the olfactory
receptors.
Mitral Cells: A neuron located in the olfactory bulb that receives information from olfactory receptors;
axons of mitral cells bring information to the rest of the brain.
Olfactory Glomerulus: A bundle of dendrites of mitral cells and the associated terminal buttons of the
axons of olfactory receptors.
The axons of the olfactory receptors pass through the perforations of the cibriform plate into the
olfactory bulbs, where they form synapses in the glomeruli with the dendrites if the mitral cells.
These neurons send axons through the olfactory tracts to the brain, principally to the amygdale, the
piriform cortex, and the entorhinal cortex.
The hippocampus, hypothalamus, and orbitofrontal cortex receive olfactory information indirectly.
Transduction of Olfactory Information
 Researchers have recognized that olfactory cilia contain receptors that are stimulated by molecules of
odorants.
 The nature of the receptors is attributed to a particular G protein, called Golf.
 When an odorant molecule binds with and stimulates one of these receptors, Golf catalyzes the synthesis
of cyclic AMP, which opens sodium channels and depolarizes the membrane.
 Aromatic molecules produce membrane potentials by interacting with a newly discovered family or
receptor molecules, which appears to contain 339 members.
Perception of Specific Odors
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Humans can recognize up to ten thousand different odorants, and other animals can probably recognize
even more.
Each glomerous receives information from only one type of olfactory receptor, and “olfactotopic”
coding is maintained all the way to the olfactory cortex.
The task of detecting odors is a spatial one; the brain recognizes odors by means of the patterns of
activity created in the olfactory cortex.
The anterior piriform cortex appears to code odor information according to the structure of the odorant
molecules, and the posterior piriform cortex codes the information it receives from the anterior region
according to the odorant’s perceptual categories.
PSYC 211
Chapter 8: Control of Movement
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Mr. J., a 48-yr-old photographer, had just had a severe stroke that damaged much of his left parietal lobe, he was
still a pleasant, cheerful, and likable man. Mr. J.’s problem is not that he cannot make skilled movements, but that
he cannot make these movements when we ask him to. He can manipulate his glasses and he can use a hammer,
but he can’t make even the simplest voluntary movements out of context. He’s able to wave at people when he is
introduced to people, even though he couldn’t do so when asked to show how to wave ‘hello’. The movement was
an automatic one that he had learned to make long ago, and it was triggered by the fact that he was meeting other
people. The parietal lobe is involved in the control of movements – especially sequences of movements – that are
not dictated by the context. Thus, he finds it almost impossible to follow verbal requests to make arbitrary
movements.
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The ultimate function of the nervous system is the control of behavior. The brain is the organ that moves the
muscles.
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Muscles
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Mammals have 3 types of muscles: skeletal muscle, smooth muscle, and cardiac muscle.
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Skeletal Muscle
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Skeletal muscles are the ones that move us, our skeleton, around and thus are responsible for our behavior. Most
of them are attached to bones at EACH end and move the bone when they contract. The exceptions include eye
muscles and some abdominal muscles, which are attached to bone at ONE end only. Muscles are fastened to
bones via tendons, strong bands of connective tissue. Contraction of a flexor muscle produces flexion, the
drawing in of a limb. Extension, which is the opposite movement, is produced by contraction of extensor muscles.
These are the so-called antigravity muscles – the ones we use to stand up. Muscles contract; limbs flex.
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Anatomy
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The skeletal muscle consists of two types of muscle fibers. The extrafusal muscle fibers are served by axons of
the alpha motor neurons. Contraction of these fibers provides the muscle’s motive force. The intrafusal muscle
fibers are specialized sensory organs that are served by two axons, one sensory and one motor. These organs are
also called muscle spindles because of their shape.
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The central region (capsule) of the intrafusal muscle fiber contains sensory endings that are sensitive to stretch
applied to the muscle fiber. There are actual 2 types of intrafusal muscle fibers, but only one is shown in the text.
The efferent axon of the gamma motor neuron causes the intrafusal muscle fiber to contract.
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A single myelinated axon of an alpha motor neuron serves several extrafusal muscle fibers. The number of muscle
fibers served by a single axon varies considerably, depending on the precision with which the muscle can be
controlled. In muscles that move the fingers or eyes the ratio can be less than 1:10; in muscles that move the leg it
can be 1:several 100. An alpha motor neuron, its axon, and associated extrafusal muscle fibers constitute a motor
unit.
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A single muscle fiber consists of a bundle of myofibrils, each of which consists of overlapping strands of actin
and myosin. The regions in which the actin and myosin filaments overlap produce dark stripes, or striations;
hence, skeletal muscle is often referred to as striated muscle.
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The physical Basis of Muscular Contraction
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The synapse between the terminal button of an efferent neuron and the membrane of a muscle fiber is called a
neuromuscular junction. The terminal buttons of the neuron synapse on motor endplates, located in grooves
along the surface of the muscle fibers. When an axon fires, acetylcholine is liberated by the terminal buttons and
produces a depolarization of the postsynaptic membrane – an endplate potential. The endplate potential is much
lager than an excitatory postsynaptic potential in synapses between neurons; an endplate potential always causes
the muscle fiber to fire, propagating the potential along its length. This action potential causes a contraction, or
twitch, of the muscle fiber.
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The depolarization of a muscle fiber opens the gates of voltage-dependent Ca2+ channels, permitting Ca2+ to enter
the cytoplasm. This event triggers the contraction. Ca2+ acts as a cofactor that permits the myofibrils to extract
energy form the ATP that is present in the cytoplasm. The myosin cross bridges alternately attach to the actin
strands, bend in one direction, detach themselves, bend back, reattach to the actin at a point farther down the
strand, and so on, resulting in the shortening of the muscle fiber.
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A single impulse of a motor neuron produces a singe twitch of a muscle fiber. The physical effects for the twitch
last longer than the AP, because of the elasticity of the muscle and the time required to rid the cell of Ca2+.
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The strength of a muscular contraction is determined by the average rate of firing of the various motor units. If, at
a given moment, many units are firing, the contraction will be forceful. If few are firing, the contraction will be
weak.
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Sensory Feedback from Muscles
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The intrafusal muscle fibers contain sensory endings that are sensitive to stretch. They are arranged in parallel
with the extrafusal fibers. Therefore, they are stretched when the muscle lengthens and are relaxed when it
shortens. Thus, even though these afferent neurons are stretch receptors, they serve as muscle length detectors.
Stretch receptors are also located within the tendons, in the Golgi tendon organ. These receptors detect the total
amount of stretch exerted by the muscle, through its tendons, on the bones to which the muscle is attached. The
stretch receptors of the Golgi tendon organ encode the degree of stretch by the rate of firing. They respond not to
a muscle’s length but how hard it is pulling. In contrast, the receptors on intrafusal muscle fibers detect muscle
length, not tension.
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What happens if a weight were suddenly dropped into your hand while your forearm was held parallel to the
ground? Neurons MS1 and MS2 (especially MS2, which responds to rapid changes in muscle length) briefly fire,
because your arm lowers briefly and then comes back to the original position, the Golgi tendon organ, monitoring
the strength of contraction, fires in proportion to the stress on the muscle, so it increases its rate of firing as soon
as the weight is added.
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Smooth Muscle
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Our bodies contain 2 types of smooth muscle, both of which are controlled by the autonomic NS. Multiunit
smooth muscles are found in large arteries, around hair follicles (where they produce piloerection, or fluffing of
fur), and in the eye (controlling lens adjustment and papillary dilation). This type of smooth muscle is normally
inactive, but it will contract in response to neural stimulation or to certain hormones. In contrast, single-unit
smooth muscles normally contract in a rhythmical fashion. Some of these cells spontaneously produce pacemaker
potentials, which we can regard as self-initiated excitatory postsynaptic potentials. These slow potentials elicit AP,
which are propagated by adjacent smooth muscle fibers, causing a wave of muscular contraction. The efferent
nerve supply (and various hormones) can modulate the rhythmical rate, increasing or decreasing it. Single-unit
smooth muscles are found chiefly in the gastrointestinal system, uterus, and small blood vessels.
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Cardiac Muscle
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Cardiac muscle is found in the heart. This type of muscle looks somewhat like striated muscle but acts like
single-unit smooth muscle. The heart beats regularly, even if it is denervated. Neural activity and certain
hormones (especially the catecholamines) serve to modulate the heart rate. A group of cells in the pacemaker of
the heart are rhythmically active and initiate the contractions of cardiac muscle that constitutes the heartbeat.
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Reflexive control of movement
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Although the brain controls behaviors, the spinal cord possesses a certain degree of autonomy. Particular kinds of
somatosensory stimuli can elicit rapid responses through neural connections located within the spinal cord. These
reflexes constitute the simplest level of motor integration.
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The Monosynaptic Stretch Reflex
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The activity of the simplest functional neural pathway in the body is easy to demonstrate: during physical
examinations a test of reflex is performed (jerk of the knee). The time interval between the patellar tendon tap and
the start of the leg extension, is about 50ms. That interval is too short for the involvement of the brain; it would
take considerably longer for sensory information to be relayed to the brain and for motor information to be
relayed back.
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The patellar reflex has no utility. However, if a more natural stimulus is applied, the utility of this mechanism
becomes apparent. Monosynaptic stretch reflex: Starting at the muscle spindle, afferent impulses are conducted
to terminal buttons in the gray matter of the spinal cord. These terminal buttons synapse on an alpha motor neuron
that innervated the extrafusal muscle fibers of the same muscle. Only one synapse is encountered along the route
from the receptor to the effector – hence the term monosynaptic.
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Now consider if the weight the person is holding is increased, the forearm begins to move down. This movement
lengthens the muscle and increases the firing rate of the muscle spindle afferent neurons, whose terminal buttons
then stimulate the alpha motor neurons, increasing their rate of firing. Consequently, the strength of the muscular
contraction increase, and the arm pulls the weight up.
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Another important role played by the monosynaptic stretch reflex is control of posture. As we stand we tend to
oscillate forward and back and from side to side. Our vestibular sacs and our visual system play important roles in
the maintenance of posture. However, these systems are aided by the activity of the monosynaptic stretch reflex.
For example, consider what happens when a person begins to lean forward. The large calf muscle (gastrocnemius)
is stretched, and this stretching elicits compensatory muscular contraction that pushes the toes down, thus
restoring upright posture.
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The Gamma Motor System
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The muscle spindles are very sensitive to changes in muscle length; they will increase their rate of firing when the
muscle is lengthened by a very small amount. The ends of the intrafusal muscle fibers can be contracted by
activity of the associated efferent axons of the gamma motor neurons; their rate of firing determines the degree of
contraction. When the muscle spindles are relaxed, they are relatively insensitive to stretch. However, when the
gamma motor neurons are active, they become shorter and hence become much more sensitive to change in
muscle length.
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Afferent axons of the muscle spindle help to maintain limb position even when the load carried by the limb is
altered. Efferent control of the muscle spindles permits these muscle length detectors to assist in changes in limb
position as well. When a single muscle spindle’s efferent axon is completely silent, the spindle is completely
relaxed and extended. As the firing rate of the efferent axon increases, the spindle gets shorter and shorter.
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When commands from the brain are issued to move a limb, both the alpha motor neurons and the gamma motor
neurons are activated. The alpha motor neurons start the muscle contracting. If there is little resistance, both the
extrafusal and intrafusal muscle fibers will contract at approximately the same rate, and little activity will be seen
from the afferent axons of the muscle spindle. However, if the limb meets with resistance, the intrafusal muscle
fibers will shorten more than the extrafusal muscle fibers, and hence sensory axons will begin to fire and cause
the monosynaptic stretch reflex to strengthen the contraction. Thus, the brain makes use of the gamma motor
system in moving the limbs. By establishing a rate of firing in the gamma motor system, the brain controls the
length of the muscle spindles and, indirectly, the length of the entire muscle.
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Polysynaptic Reflexes
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The monosynaptic stretch reflex in the only spinal reflex we know of that involves only one synapse. All others
are polysynaptic. Examples include relatively simple ones, such as limb withdrawal in response to noxious
stimulation, and relatively complex ones, such as the ejaculation of semen. Spinal reflexes do not exist in isolation;
they are normally controlled by the brain.
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The afferent axons from the Golgi tendon organ serve as detectors of muscle stretch. There are two populations of
afferent axons form the Golgi tendon organ, with different sensitivities to stretch. The more sensitive afferent
axons tell the brain how hard the muscle is pulling. The less sensitive ones have an additional function. Their
terminal buttons synapse on spinal cord interneurons – neurons that reside entirely within the gray matter of the
spinal cord and serve to interconnect other spinal neurons. These interneurons synapse on the alpha motor neurons
serving the same muscle. The terminal buttons liberate glycine and hence produce inhibitory postsynaptic
potentials on the motor neurons.
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The function for this reflex pathway is to decrease the strength of muscular contraction when there is danger of
damage to the tendons or bones to which the muscles are attached. Weight lifters can lift heavier weights if their
Golgi tendon organs are deactivated with injections of a local anesthetic, but they run the risk of pulling the
tendon away from the bone or even breaking the bone.
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A decerebrate cat, whose brain stem has been cut through, exhibits a phenomenon known as decerebrate
rigidity. The animal’s back is arched, and its legs are extended stiffly from its body. This rigidity results from
excitation originating in the caudal reticular formation, which greatly facilitates all stretch reflexes, especially of
extensor muscles, by increasing the activity of the gamma motor system. Rostral to the brain stem transaction is
an inhibitory region of the reticular formation, which normally counterbalances the excitatory one. The
transaction removes the inhibitory influence, leaving only the excitatory one. If you attempt to flex the
outstretched leg of a decerebrate cat, you will meet with increasing resistance, which suddenly melts away,
allowing the limb to flex. It almost feels as though you were closing the blade of a pocketknife – hence the term
clasp-knife reflex. The sudden release is, of course, mediated by activation of the Golgi tendon organ reflex.
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Even the monosynaptic stretch reflex serves as the basis of polysynaptic reflexes. Muscles are arranged in
opposing pairs. The agonist moves the limb in the direction being studied, and because muscles cannot push back
the antagonist muscle must move the limb back in the opposite direction.
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Afferent axons of the muscle spindles, besides sending terminal buttons to the alpha motor neuron and to the brain,
also synapse on inhibitory interneurons. The terminal buttons of these interneurons synapse on the alpha motor
neurons that innervate the antagonistic muscle. Thus, a stretch reflex excites the agonist and inhibits the
antagonist so that the limb can move in the direction controlled by the stimulated muscles.
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Control of Movement by the Brain
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Because there is no single cause of behavior, we cannot find a single starting point in our search for the neural
mechanisms that control movement. The CNS includes many different motor systems that can both control
particular kinds of movements at the same time. Walking, postural adjustments, talking, movement of the arms,
and movements of the fingers all involve different specialized motor systems.
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Organization of Motor Cortex
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The primary motor cortex lies on the precentral gyrus, just rostral to the central sulcus. The primary motor cortex
shows somatotopic organization. The motor homunculus is based on the observations of Penfield and
Rasmussen. Note that a disproportionate amount of cortical area is devoted to movements of the fingers and the
muscles used for speech.
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Recognize that the primary motor cortex is organized in terms of particular movements of particular parts of the
body. Complex neural circuitry is located between individual neurons in the primary motor cortex and the motor
neurons in the spinal cord that cause motor units to contract. The commands for movement initiated in the motor
cortex are assisted and modified – most notably by the basal ganglia and the cerebellum.
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A study by Graziano and Aflalo found that although brief stimulations of particular regions of the primary motor
cortex of moneys caused brief movements of various part of the body, prolonged stimulation produced much
more complex movements.
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The principal cortical input to the primary motor cortex is the frontal association cortex, located rostral to it. Two
regions immediately adjacent to the primary motor cortex – the supplementary motor area and the premotor
cortex – are especially important in the control of movement. Both regions receive sensory information form the
parietal and temporal lobes, and both send efferent axons to the primary motor cortex. The supplementary motor
area (SMA) is located on the medial surface of the brain, just rostral to the primary motor cortex. The premotor
cortex is located primarily on the lateral surface, also just rostral to the primary motor cortex.
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The primary motor cortex also receives projections from the adjacent primary
somatosensory cortex, located just across the central sulcus. Neurons in the primary somatosensory cortex that
respond to stimuli applied to a particular part of the body send axons to neurons in the primary motor cortex that
move muscles in the same part of the body.
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Asanuma and Rosén found that somatosensory neurons that respond to a touch on the
back if the thumb send axons to motor neurons that cause thumb extension, and somatosensory neurons that
respond to touch on the ball of the thumb send axons to motor neurons that cause thumb flexion. This
organization appears to provide rapid feedback to the motor system during manipulation of objects.
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Cortical Control of Movement: The Descending Pathways
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Neurons is the primary motor cortex control movements by two groups of descending
tracts, the lateral group and the ventromedial group, named for their locations in the white matter of the spinal
cord. The lateral group consists of the corticospinal tract, the corticobulbar tract, and the rubrospinal tract. This
system is primarily involved in control of independent limb movements, particularly movements of the hands and
fingers. Independent limb movements mean that the right and left limbs make different movements or one limb
moves while the other remains still. These movements contrast with coordinated limb movements such as those
involved in locomotion. The ventromedial group consists of the vestibulospinal tract, the tectospinal tract, and
the ventral corticospinal tract. These tracts control more automatic movements: gross movement of the muscles
of the trunk and coordinated trunk and limb movements involved in posture and locomotion.

Let’s first consider the lateral group of descending tracts. The corticospinal tract
consists of axons of cortical neurons that terminate in the gray matter of the spinal cord. The axons leave the
cortex and travel through subcortical white matter to the ventral midbrain, where they enter the cerebral peduncles.
They leave the peduncles in the medulla and from the pyramidal tracts, so-called because of their shape. At the
level of the caudal medulla, most of the fibers decussate (cross over) and descend through the contralateral spinal
cord, forming the lateral corticospinal tract. The rest of the fibers descend through the ipsilateral spinal cord,
forming the ventral corticospinal tract.
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Most of the axons in the lateral corticospinal tract originate in the regions of the
primary motor cortex and supplementary motor area that control the distal parts of the limbs: the arms, hands,
fingers, lower legs, feet, and toes. They form synapses, directly or via interneurons, with motor neurons in the
gray matter o the spinal cord – in the lateral part of the ventral horn. These motor neurons control muscles of the
distal limbs, including those that move the arms, hands, and fingers.
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The axons in the ventral corticospinal tract originate in the upper leg and trunk regions
of the primary motor cortex. They descend to the appropriate region of the spinal cord and divide, sending
terminal buttons into both sides of the gray matter. They control motor neurons that move the muscles of the
upper legs and trunk.
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The corticospinal pathway controls hand and finger movements and is indispensable
for moving the fingers independently when reaching and manipulating. Postural adjustments of the trunk and use
of the limbs for reaching and locomotion are unaffected; therefore, these types of movements are controlled by
other systems. Because the monkeys had difficult releasing their grasp when they picked up objects but had no
trouble doing so when climbing the walls of the cage, we can conclude that the same behavior is controlled by
different brain mechanisms in different contexts.
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The second of the lateral group of descending pathways, the corticobulbar tract,
projects to the medulla (sometimes called the bulb). This pathway is similar to the corticospinal pathway, except
that it terminates in the motor nuclei of the 5th, 7th, 9th, 10th, 11th, and 12th cranial nerves. These nerves control
movements of the face, neck, tongue, and parts of the extraocular eye muscles. [see green line in Fig 8.11]
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The third member of the lateral group is the rubrospinal tract. This tract originates in
the red nucleus (nucleus ruber) of the midbrain. The red nucleus receives its mort important inputs from the motor
cortex via the corticorubral tract and from the cerebellum. Axons of the rubrospinal tracts terminate on motor
neurons in the spinal cord that control movements of forelimb and hindlimb muscles. [see red line in Fig. 8.11]

Now let’s consider the second set of pathways originating in the brain stem: the
ventromedial group. This group includes the vestibulospinal tracts, the tectospinal tracts, and the
reticulospinal tracts, as well as the ventral corticospinal tract. These traits control motor neurons in the
ventromedial part of the spinal cord gray matter. Neurons of all these reacts receive input from the portions of the
primary motor cortex that control movements of the trunk and proximal muscles. In addition, the reticular
formation receives a considerable amount of input from the premotor cortex and from several subcortical regions,
including the amygdala, hypothalamus, and basal ganglia. The cell bodies of neurons of the vestibulospinal tracts
are located in the vestibular nuclei. As you might expect, this system plays a role in the control of posture. The
cell bodies of neurons in the tectospinal tracts are located in the superior colliculus and are involved in
coordinating head and trunk movements with eye movements. The cell bodies of neurons of the reticulospinal
tracts are located in many nuclei in the brain stem and midbrain reticular formation. These neurons control several
automatic functions, such as muscle tonus, respiration, coughing, and sneezing; but they are also involved in
behaviors that are under direct neocortical control, such as walking. [see Fig. 8.12]

Table 8.1 summarizes the names of these pathways, their locations, and the muscle
groups they control.


Planning and Initiating Movements: Role of the Motor Association Cortex


The motor association cortex is also involved in imitating the actions of other people
(an ability that makes it possible to learn new behaviors from them) and even in understanding the functions of
other people’s behavior.


The supplementary motor area and the premotor cortex receive information from
association areas of the parietal and temporal cortex. The visual association is organized in 2 streams: dorsal and
ventral. The ventral stream, which terminates in the inferior temporal cortex, is involved in perceiving and
recognizing particular objects – the “what” of visual perception. The dorsal stream, which terminates in the
posterior parietal lobe, is involved in perception of location – the “where” of visual perception. In addition, the
parietal lobes are involve in organizing visually guided movements – the “how” of visual perception. Besides
receiving visual information about space, the parietal lobe receives information about spatial location from the
somatosensory, vestibular, and auditory systems and integrates this information with visual information. Thus, the
regions of the frontal cortex involved in planning movements receive the information they need about what is
happening and where it is happening from the temporal and parietal lobes. Because the parietal lobes contain
spatial information, the pathway from them to the frontal lobes is especially important in controlling both
locomotion and arm and hand movements. After all, meaningful movements of our arms and hands rewire us to
know where objects are located in space.


The supplementary motor cortex is involved in learning and performing behaviors that
consist of sequences of movements. The premotor cortex is involved in imitating responses of other people and in
understanding and predicting these actions.


The Supplementary Motor Area (SMA)


The supplementary motor area plays a critical role in behavioral sequences. Damage to
this region disrupts the ability to execute well-learned sequences off responses in which the performance of one
response serves as the signal that the next response must be made. Chen et al. found that lesions of the
supplementary motor area severely impaired monkey’s ability to perform: pushing a lever in and then turning it to
the left, receiving a peanut after each response.


Mushiake, Inase, and Tanji trained monkeys to perform a memorized series of
responses, pressing each of 3 buttons is a specific sequence. While the monkeys were performing this task, more
than half of the neurons in the supplementary motor area became activated. However, when the sequence was
cued by visual stimuli – the monkeys simply had to press the button that was illuminated – these neurons showed
little activity.


Shima and Tanji taught monkeys six sequences of three motor responses. Ex: one of
the sequences was push, then pull, then turn. They recorded from neurons in the supplementary motor area and
found neurons whose activity appeared to encode elements of these sequences. Ex: some neurons responded just
before a particular sequence of three movements occurred; some neurons responded between 2 particular
responses; and some neurons responded as the monkey was preparing to make the last response of the sequence.
Presumably, these neurons were members of circuits that encoded the information necessary to perform the 6
sequences.


Shima and Tanji temporarily inactivated the supplementary motor area in more with
injections of muscimol, a drug that stimulates GABA receptors and this inhibits neural activity. They found that
after inactivation of this region, monkeys could still reach for objects or make particular movements in response
to visual cues, but they could no longer make a sequence of 3 movements they had previously learned.


Studies with human subjects have obtained results similar to those obtained with
monkeys. Ex: a fxnl imaging study by Hikosaka et al. observed increased activity in the posterior SMA during
performance of a learned sequence of button presses. Gerloff et al. taught people to make a sequence of 16 finger
presses on an electric piano. When the experimenters disrupted the activity of the SMA with transcranial magnetic
stimulation, the performance of the sequence was disrupted. However, the disruption was not immediate: the
subjects continued the sequence for approximately and second and then stopped, saying that they “did not know
anymore which series of keys to press next.” Apparently, the SMA is involved in planning the elements yet to
come in sequences of movements. The actual execution of the movements appears to be controlled elsewhere –
presumably, by the primary motor cortex.



A region just anterior to the supplementary motor area, the pre-SMA, appears to be
involved in control of spontaneous movements – or at least in the perception of control. It has long been known
that although electrical stimulation of the motor cortex causes movements, it does not produce the desire to move.
The movement is perceived as automatic and involuntary. In contrast, electrical stimulation of the medial surface
of the frontal lobes often provokes the urge to make a movement, or at least the anticipation that a movement is
about to occur.

A functional imaging study by Lau et al. found that the pre-SMA became active just
before people performed spontaneous movements. The experimenters asked the subjects to make a finger
movement from time to time, whenever they felt liked doing so. The subjects watched a red light that moved
around a clock face at about 2.5s/rev. They were asked to pay attention to the instant when they decided to make
the movement and report the position of the red dot at that time. The decision appeared to occur approximately
0.2s before the movement began. However, fMRI showed that the activity of the pre-SMA actually began to
increase approximately 2-3s earlier than that, which suggests that the neural activity responsible for the decision
to move begins before a person is even aware of making that decision.


The most important input to the supplementary motor area comes from the parietal
lobes. Sirigu et al. used a task similar to the one by Lau et al. to investigate decision making in people with lesions
of the parietal cortex. They found that people with parietal lesions could accurately report when they started the
movement, but they were not aware of an intention to move prior to making the movement. These results suggest
that information received from the parietal lobes permit the pre-SMA to detect that a decision to move has been
made. The location of the neural circuits actually responsible for the decision are not known, although Sirigu et al.
note that lesions of the prefrontal cortex disrupt people’s plans for voluntary actin. People with prefrontal lesions
will react to events but show deficits in initiating behavior, so perhaps the prefrontal cortex is an important source
of these decisions.


Premotor Cortex


The premotor cortex is involved in learning and executing complex movements that
are guided by sensory information. Reaching for an object that we see in a particular location involves
nonarbitrary spatial information – that is, the visual information provided buy the location of the object specifies
just where we should target our reaching movement. But we also have the ability to learn to make movements
based in arbitrary information – information that is not directly related to the movement that it signals. Ex: person
points to an object when its called out, following dance moves, “wave your L hand when you hear the buzz and
touch you nose when you hear the bell.” The associations between these stimuli and the movement they designate
are arbitrary and must be learned.


Kurata and Hoffman trained monkeys to move their hand toward the right or left in
response to either a spatial or a nonspatial signal. The spatial signal required the animals to move in direction
indicated by signal lights located to the right and left of its hand. The nonspatial signal consisted of a pair of lights,
one red and one green, located in the middle of the display. The red light signaled a movement to the left, and the
green light signals a movement to the right The investigators temporarily inactivated the premotor cortex with
injections of muscimol. When this region was inactivated, the monkeys could still move their hand toward a
signal light located to the left or right, but they could no longer make the appropriate movements when the red or
green signal sights were illuminated.


Similar results are seen in people with damages to the premotor cortex. Halsband and
Freund found that patients with these lesions could learn to make six different movements in response to spatial
cues but not to arbitrary visual cues. That is, they could learn to point to one of six locations is which they had just
seen a visual stimulus, but they could not learn to use a set of visual, auditory, and tactile cues to make particular
movements.



Imitating and Comprehending Movements: Role of the Mirror Neuron System


Rizzolatti et al. found that neurons is an area of the rostral part of the ventral premotor
cortex in the monkey brain became active when monkeys saw people or other monkey perform various grasping,
holding, or manipulative movements or when they performed these movements themselves. Thus, the neurons
responded to either the sight or the execution of particular movements. The investigators named these cells
mirror neurons. The site of these neurons, the ventral premotor cortex, is reciprocally connected with the
inferior parietal lobule, a region of the posterior parietal lobe, and further investigation found that this region also
contains mirror neurons. Given the characteristics of mirror neurons, we might expect that they play a role in a
money’s ability to imitate the movements of other monkeys – and this inference was correct.


Several functional-imaging studies have shown that the human brain also contains a
circuit of mirror neurons in the inferior parietals lobule and the ventral premotor area. In a study performed by
Buccino et al. asked non-musicians to watch and then imitate video clips of an expert guitarist placing his finger
on the neck of a guitar to play a chord. The investigators found that nth watching and imitating the movements
activated the mirror neuron circuit. Several studies have found that the mirror neuron system is activated most
strongly when one is watching a behavior in which one is already competent. Ex: Calvo-Merino et al. had
professional ballet dancers, professional capoeira dancers, and non-experts watch videos of dancers performing
ballet and capoeira movements. All subjects showed activations of the mirror neuron system. The professional
dancers showed more activation than the non-experts did, and the two groups of dancers showed greater
activation when they watched the kind of dance in which they were proficient.



Mirror neurons are activated not only by the performance of an action or the sight of
someone else performing tat action, but also by sounds that indicate the occurrence of a familiar action. Ex:
Kohler et al. found that mirror neurons in the ventral prefrontal cortex of monkeys became active when the
animals heard sounds they recognized such as a peanut breaking, a piece of paper being ripped, or a stick being
dropped. Individual neurons – the researchers called them audiovisual neurons – responded to the sound of
particular actions and to the sight of those actions. Presumably, activation for these neurons by these familiar
sounds reminds the animals of the actions the sounds represent. Lahav, Saltzman, and Schlaug found that the
connections of audiovisual neurons could be established very quickly. The investigators taught non-musicians to
play a simple tine on a piano. Next, they obtained fMRI scans from the subjects while they listened to the tune
they had learned and, as control conditions, listened to familiar tunes that thy had not learned t play and to the
same notes they had played but in a different order. Although the subjects rested quietly in the scanner without
moving, their frontoparietal mirror neuron network was activated when they heard the tune they had learned to
play.

Haslinger et al. found that the interaction between audition and vision worked in the
other direction as well. The investigators showed professional pianists silent videos of a hand playing the piano or
making meaningless finger movements above piano keyboard. Functional imaging showed that when the subjects
watched actual piano playing, the mirror neuron system and visual cortex were activated as well. Presumably, the
musicians imagines what it was like to male the meaningful hand and finger movements, activating the mirror
neuron system, but also imagined what the piano would sound like when the keys were pressed, activating the
auditory cortex.


Rizzolatti, Fogassi, and Gallese suggest that the mirror neuron circuit helps us to
understand the actions of other. The neural circuits responsible for performing a particular action are activated
when we see someone else beginning to perform that action or even when we hear the characteristic sounds
produced by that action. Feedback from the activation of these circuits gives rise to the recognition of the action.


A functional imaging study by Iacoboni et al. suggests that the mirror neuron system
helps us to understand other people’s intentions. They showed subjects video clips of an arm and hand reaching
for and grasping a drinking mug. The actions were shown in isolation or in the context of objects set out for a
snack or the same objects after the snack had been eaten. The first context suggests that the intent of the action is
that of drinking, and the second suggests that the intent is that of cleaning up. The investigators found that
watching the reaching action activated the mirror neuron system of the ventral premotor cortex, but there were
differences in the activation when the action occurred in the two different contexts. The authors concluded that the
mirror neuron system encodes not only an action but the intent of that action.


Control of Reaching and Grasping


Much of our behavior involves interacting with objects in our environment.
Researchers investigating these interactions classify them into 2 major categories: reaching and grasping. It turns
out that different brain mechanisms are involved in these two activities.


Most reaching behavior is controlled by vision. The dorsal stream of the visual system
is involved with the location movement, direction and speed of the object. Connections between the parietal lobe
and the frontal lobe play a critical role in reaching. Several regions of the visual association cortex are named for
particular types of objects that we perceive, ex: FFA, EBA, and PPA. One region of the medial posterior parietal
cortex has been named the parietal reach region. Connolly, Anderson, and Goodale found that when people
were about to make a pointing or reaching movement to a particular location this region became active.
Presumably, the parietal cortex determines the location of the target and supplies information about this location
to motor mechanisms in the frontal cortex.


Another region of the posterior cortex, the anterior part of the intraparietal sulcus
(aIPS), is involved in controlling hand and finger movements involved in grasping the target object. A functionalimaging study by Frey et al. had people reach for objects of different shapes, which required them to make a
variety of hand and finger movements to hold onto the objects. The brain activity directly related to grasping
movements was determined by subtracting the activity produced by reaching for and simply touching the objects
from the activity produced by reaching for and grasping the objects. The grasping activity activated the aIPS.


An experiment by Tunik, Frey, and Grafton confirmed the importance of the aIPS to
grasping. The investigators had subjects reach for and grasp a rectangular object that was oriented with its long
side in a vertical horizontal position. On some trails the object rotated during the subjects’ reaching movements,
which required the subjects to adjust the position of their hand or fingers before they reached the object. On some
of these perturbed trials the investigators applied TMS that disrupted the activity of the aIPS. When the disruptive
stimulation occurred within 65ms after the rotation of the object, the subject’s ability to accurately change grip
posture was disrupted. Stimulation of the hand area of the primary motor cortex or other part of the parietal lobe
had no effect.


The visual input to the aIPS is from the dorsal stream of the visual system. In a
functional-imaging study by Shmuelof and Zohary, subjects watched brief videos of a hand reaching or to grasp a
variety of objects. Sometimes the hand appeared in the left visual field and the object appeared in the right visual
field; sometimes the locations for the hand and the object were reversed. This procedure means that for a
particular trial, visual information about an object was transmitted to one side of the brain. Analysis of the brain
activated the ventral stream of the visual system and information about the shape of the hand activated the aIPS –
part of the dorsa stream. The results suggest that the aIPS is involved in recognition of grasping movements as
well as their execution.


Deficits of Skilled Movements: The Apraxias


Damage to the frontal or parietal cortex on the left side of the brain can produce a
category of deficits called apraxia (without action). It refers to the inability to imitate movements or produce
them in response to verbal instructions or inability to demonstrate the movements that would be made in using a
familiar tool or utensil. Neuropsychological studies of the apraxias have provided information about the way
skilled behaviors are organized and initiated.


There are 4 major types of apraxia. Limb apraxia refers to problems with movements
of the arms, hands, and fingers. Oral Apraxia refers to problems with movements of the muscles used in speech.
Apraxic agraphia refers to a particular type of writing deficit. Constructional apraxia refers to difficulty in
drawing or constructing objects.



Limb Apraxia

It’s characterized by movement of the wrong part of the limb, incorrect movement of
the correct part, or correct movements but in the incorrect sequence. This is assed through imitation. It’s very
difficult in carrying out an action without the object that is normally acted upon.


To perform behaviors on verbal command without having a real object to manipulate,
a person must comprehend the command and be able to imagine the missing article as well as to make the proper
movements; therefore, these requests are the most difficult to carry out. It’s easier to imitating the behavior
performed by the experimenter. But the easiest task is to use the object.


Why does damage to the left parietal hemisphere, but usually not the right, cause an
apraxia of both hands? The answer is that the right hemisphere is involved wit one’s own body. A functional
imaging study by Chaminade, Meltzoff, and Decety supports this explanation. The investigators asked subjects to
watch another person perform hand and arm gestures and then either imitate the gestures or make different ones
with the same arm or the other arm. On the basis of the activity seen by fMRI scans, the authors concluded that
posterior regions of the right hemisphere tracked the movements of the model in space, while the left parietal lobe
organized the movements that would be made in response.


The frontal cortex appears to also play a more important role in recognizing the
meaning of these gestures. Pazzaglia et al. tested 33 patients with damage to the left hemisphere and 8 patients
with damage to the right hemisphere and found that 21 of them with the left hemisphere damaged had limb
apraxia. They tested for recognition of hand gestures by having them watch video clips in which a person
performed the gestures correctly or incorrectly (ex: playing a broom as a guitar). Apraxic patients with damage to
the inferior frontal gyrus, but not to the parietal cortex, showed deficits in comprehension of the gestures.


Constructional Apraxia


It’s caused by lesions of the right hemisphere, particularly the right parietal lobe. They
have trouble drawing pictures or assembling objects from elements such as toy building blocks. The primary
deficit in constructional apraxia appears to involve the ability to perceive and imagine geometrical relations.
Because of this deficit, a person cannot draw pictures. Ex: a cube because they cannot imagine what the lines and
angles of a cube look lie, not because of difficulty controlling the movements of his or her arm and hand.


The Basal Ganglia

Anatomy and Function


The basal ganglia constitute an important component of the motor system. The motor
nuclei of the basal ganglia include the caudate nucleus, putamen, and globus pallidus. The basal ganglia receive
most of their input from all regions of the cerebral cortex and the substantia nigra. They have two primary outputs:
(1) the primary motor cortex (via the thalamus) and (2) motor nuclei of the brain stem that contribute to the
ventromedial pathways. Through these connections the basal ganglia influence movements under the control over
the ventromedial system.


Components of the basal ganglia: caudate nucleus, the putamen, and globus pallidus.
Nuclei Association with the basal ganglia: the ventral anterior nucleus and ventrolateral nucleus of the thalamus
and the substania nigra of the ventral midbrain. [see Fig 8.24a]


The frontal, parietal, and temporal cortex sends axons to the caudate nucleus and the
putamen, which then connect with the globus pallidus. The globus pallidus sends information back to the motor
cortex via the ventral anterior and ventrolateral nuclei of the thalamus, completing the loop. They can influence
the movements controlled by the motor cortex since they receive this info of the movements being planned and
executed by the motor cortex. Throughout this circuit, information is represented somatotopically.


Another important input to the basal ganglia comes from the substantia nigra of the
midbrain. Ch4 showed that degeneration of the nigrostiata; bindle the dopaminergic pathway from the substania
nigra to the caudate nucleus and putamen causes Parkinson’s disease.


The links in the loop are made by both excitatory (glutamate-secreting) neurons and
inhibitory (GABA-secreting) neurons. The caudate nucleus and putamen receive excitatory input from the
cerebral cortex. They send inhibitory axons to the external and internal division of the globus pallidus (the GPi
and the GPe, respectively). The pathway that includes the GPi is known as the direct pathway (arrows with solid
lines). Neurons in GPi send inhibitory axons to the ventral anterior (VA) and ventrolateral (VL) thalamus, which
send excitatory projections to the motor cortex. The net effect for the loop is excitatory because it contains two
inhibitory links. Each inhibitory link (red arrow) reversed the sign of the input to that link. Thus, excitatory input
to the caudate nucleus and putamen causes these structures to inhibit neurons in the GPi. This inhibition removes
the inhibitory effect of the connections between the GPi on the VA/VL thalamus; in other words neurons in the
VA/VL thalamus become more excited. This excitation is passed on to the motor cortex.


The pathway that includes the GPe is known as the indirect pathway (arrows with
broken lines). Neurons in GPe send inhibitory input to the subthalamic nucleus, which sends excitatory input to
GPi. From there on, the circuit is identical to the one above except that the ultimate effect of this loop on the
thalamus and frontal cortex in inhibitory. The globus pallidus also sends axons to various motor nuclei in the
brain stem that contribute to the ventromedial system.


Parkinson’s Disease


Primary symptoms are muscular rigidity, slowness of movement, a resting tremor, and
postural instability. Ex: once seated, it’s difficult to arise. Writing is slow and labored and the letter get smaller
and smaller as it progresses. Parkinson’s disease also produces a resting tremor - vibratory movements of the
arms and hands that diminish somewhat of the arms and hands that diminish somewhat when the individual
makes purposeful movements. The tremor is accompanied by rigidity; the joints appear stiff. The tremor and
rigidity are NOT the cause of slow movements.


Damage to the nigrostriatal bundle causes slowness of movements and disrupts
postural adjustments. Normal movements require an appropriate balance between the direct (excitatory) and in
direct (inhibitory) pathways. The caudate nucleus and putamen consist of 2 different zones, both of which receive
input from dopaminergic neurons of the substania nigra. One of these zones contains D1 dopamine receptors,
which produce excitatory effect. Neurons in this zone send their axons to the GPi. Neurons in the other zone
contain D2 receptors, which produce inhibitory effects. These neurons send their axons to the GPe. [Fig 8.24b].
The first of these circuits, beginning with the black arrow form the substantia nigra, goes through two inhibitory
synapses (red arrows) before it reached the VA/VL thalamus; thus this circuit has an excitatory effect on behavior.
The second of these circuits begins with an inhibitory input to the caudate nucleus and putamen, but it goes
through 4 inhibitory synapses in the following pathway: substantia nigra  caudate/putamen  GPe 
subthalamic nucleus  GPi  VA/VL thalamus. Thus, the effect of this pathway too, is excitatory; thus,
dopaminergic input to the caudate nucleus and putamen facilitate movements. Note that the GPi also sends axons
to the ventromedial system. A decrease in this inhibitory output is probably responsible for the muscular rigidity
and poor control of posture seen in Parkingson’s disease.


The standard treatment for Parkinson’s disease is L-DOPA, the precursor of dopamine.
When an increased amount of L-DOPA is resent, the remaining nigrostriatal dopaminergic neurons in a patient
with Parkinson’s disease will produce and release more dopamine. But this compensation often produces
dyskinesias and dystonias – involuntary movements and postures that are presumably cased by too much
stimulation of dopamine receptors in the basal ganglia.


Huntington’s Disease


Another basal ganglia disease, Huntington’s disease, is caused by degeneration of the
caudate nucleus and putamen, especially of the GABA-ergic and ACh-ergic neurons. It causes uncontrollable
movements, especially jerky limb movements.


The symptoms begin in the 30s or 40s of a patient. The first signs occur in the
medium-sized spiny inhibitory neurons whose axons travel to the external division of the globus pallidus. The loss
of inhibition provided by these GABA-secreting neurons increases the activity of the GPe, which then inhibits the
subthalamic nucleus. Then the activity level of the GPi decreases, and excessive movements occur. As the disease
progresses, the caudate nucleus and putamen degenerate until almost all of their neurons disappear.


It’s a hereditary disorder, caused by a dominant gene on chromosome 4. It has a defect
of a repeated chain of aa glutamine. This chain produces a protein huntingtin.


The Cerebellum


It contain about 50 billion neurons compared to the ~22 billion neurons in the cerebral
cortex. The cerebellum consists of 2 hemispheres that contain several deep nuclei. The medial part of the
cerebellum is phylogenetically older than the lateral part, and it participates in control of the ventromedial system.
The flocculonodular lobe, located at the caudal end of the cerebellum, receives input from the vestibular system,
and projects axons to the vestibular nucleus. It’s also involved in the postural reflexes [green lines in Fig. 8.26].
The vermis, located on the midline, receives auditory and visual information from the tectum and cutaneous and
kinesthetic information from the spinal cord. It sends its outputs to the fastigial nucleus, which then sends it to
the vestibular nucleus and to motor nuclei in the reticular formation.


The rest of the cerebellar cortex receives most of its input form the cerebral cortex,
including the primary motor cortex and association cortex. This input is relayed to the cerebellar cortex thought
the pontine tegmental reticular nucleus. The intermediate zone of the cerebellar cortex projects to the interposed
nuclei, which in turn project to the red nucleus. Thus, the intermediate zone influences the control of the
rubrospinal system over movement of the arms and legs. The interposed nuclei also send outputs to the
ventrolateral thalamic nucleus, which projects to the motor cortex. [see red lines in Fig 8.26]


The lateral zone of the cerebellum is involved in the control of independent limb
movements are initiated by neurons in the frontal association cortex. But although the frontal cortex can plan and
initiate movements, it does not contain the neural circuitry needed to calculate the complex, closely timed
sequences of muscular contractions that are needed for rapid, skilled movements. That task falls to the lateral zone
of the cerebellum.


Both the frontal association cortex and the primary motor cortex send information
about intended movements to the lateral zone of the cerebellum via the pontine nucleus. The lateral zone also
receives information from the somatosensory system, which informs it about the current position and rate of
movement of the limbs – information that is necessary for computing the details of a movement. The results of
this computation are sent to the denate nucleus, another of the deep cerebellar nuclei. Neurons in the dentate
nucleus pass the information onto the ventrolateral thalamus, which projects to the primary motor cortex. The
projection from the ventrolateral thalamus to the primary motor cortex enables the cerebellum to modify the
ongoing movement that was initiated by the frontal cortex. The lateral zone of the cerebellum also send efferent to
the red nucleus; thus it helps to control independent limb movements through this system as well. [Fig 8.27]



In humans, lesions of different regions of the cerebellum produce different symptoms.
Damage to the flocculonodular lobe or the vermis causes disturbances in posture and balance. Damage to the
intermediate zone produces deficits in movements controlled by the rubrospinal system; the principal symptom of
this damage is limb rigidity. Damage to the lateral zone causes weakness and decomposition of movement.

Lesions if the lateral zone of the cerebellar cortex also appear to impair the timing of
rapid ballistic movement. Ballistic movements occur too fast to be modified by feedback. The sequence of
muscular movements must then be programmed in advance, and the individual muscles must be activated at the
proper times.


Kornhuber suggested that one of the primary functions of the cerebellum is timing the
duration of rapid movements. Obviously, learning must pay a role in controlling such movement.


Timmann, Watts, and Hore reported an interesting example of the role the cerebellum
plays in timing sequences of muscular contractions. When tossing a ball at a target using an over arm throw, a
person raised their hand above the shoulder, rotates the arm forward, and then releases the ball by extending the
fingers – moving them apart. The timing of the release is critical: too soon and the ball goes too high too late and
it goes too low. The researchers found that normal subjects released the ball within a 11ms window 95% of the
time. Patients with cerebellar lesions did 5 times worse the window was 55ms.


Thach obtained experimental evidence that corroborates this role. He found that many
neurons in the dentate nuclei (which receives inputs form the lateral zone of the cerebellar cortex) showed
response patterns that predicted the next movement is a sequence rather than the one that was currently taking
place. Presumably, the cerebellum as planning these movements.


The Reticular Formation


The reticular formation consists of a large number of nuclei located in the core of the
medulla, pons, and midbrain. The reticular formation controls the activity of the gamma motor system and hence
regulates muscle tonus. In addition, the pons and medulla contain several nuclei with specific motor functions. Ex:
different location on the medulla control automatic or semiautomatic responses such as respiration, sneezing,
coughing, and vomiting. The ventromedial pathways originate in the superior colliculi, vestibual nuclei, and
reticular formation. Thus, the reticular formation plays a role in the control of posture.


The reticular formation also plays a role in locomotion. Stimulation of the
mesencephalic locomotor region, located ventral to the inferior colliculus, causes a cat to make pacing
movements. It controls the activity of reticulospinal tract neurons. No direct fibers lead to the brain.


Other motor fxns of the reticular formation are also being discovered. Siegel and
McGinty recorded from 35 single neurons in the reticular formation of unanesthetized, freely moving cats. 32 of
these neurons responded during specific movements of the head, tongue, facial muscles, ears, forepaw, or
shoulder. The specific nature of the relationships suggests that the neurons play some role in controlling the
movements. Ex: one neuron responded when the tongue moved out and to the left.


Glossary
Term
Definition
Skeletal muscle
One of the striated muscles attached to bones
Flexion
A movement of a limb that tends to bend it joints; the opposite of extension
Extension
A movement of a lib that tends to straighten its joint; the opposite of flexion
Extrafusal muscle fiber
One of the muscle fibers that are responsible for the force exerted by
contraction of a skeletal muscle
Alpha motor neuron
A neurons whose axon forms synapses with extrafusal muscle fibers of a
skeletal muscle; activation contracts the muscle fibers.
Intrafusal Muscle fiber
A muscle fiber that functions as a stretch receptor, arranged parallel to the
extrafusal muscle fibers, thus detecting changes in muscle length
Gamma motor neuron
A neuron whose axon form synapses with intrafusal muscle fibers
Motor unit
A motor neuron and its associated muscle fibers
Myofibril
An element of muscle fibers that consists of overlapping strands of actin and
myosin; responsible for muscular contractions
Actin
One of the proteins (with myosin) that provide the physical basis for muscular
contraction.
Myosin
One of the proteins (with actin) that provide the physical basis for muscular
contraction.
Striated Muscle
Skeletal muscle; muscle that contain striations
Neuromuscular junction
The synapse between the terminal buttons of an axon and a muscle fiber
Motor endplate
The postsynaptic membrane of a neuromuscular junction
Endplate potential
The postsynaptic potential that occurs in the motor endplate in response to
release of Ach by the terminal button
Golgi tendon organ
The receptor organ at the junction of the tendon and muscle that is sensitive to
stretch
Smooth muscle
Nonstriated muscle innervated by the autonomic NS, found in the walls of
blood vessels, in the reproductive tats, in sphincters, within the eye, in the
digestive system, and around hair follicles
Cardiac muscle
The muscle responsible for the contraction of the heart
Monosynaptic stretch
reflex
A reflex in which a muscle contracts in response to its being quickly stretched;
involves a sensory neuron and a motor neuron, with one synapse between them.
Decerebrate
Describes an animal whose brain stem has been transected
Decerebrate rigidity
Simultaneous contraction of agonistic and antagonistic muscle; caused by
decerebration or damage to the reticular formation
Claps-knife reflex
A reflex that occurs when force is applied to flex or extend the limb of an
animal showing decerebrate rigidity; resistance is replaced by sudden
relaxation
Agonist
A muscle whose contraction produces or facilitates a particular movement
Antagonist
A muscle whose contraction resists or reverses a particular movement
Somatotopic
organization
A topographically organized aping of parts of the body that are represented in a
particular region of the brain
Supplementary motor
area (SMA)
A region of motor association cortex of the dorsal and dorsomedial frontal
lobe, rostral to the primary motor cortex
Premotor cortex
A region of motor association cortex of the lateral frontal lobe, rostral to the
primary motor cortex
Lateral group
The corticospinal tract, the corticobulbar tract, and the rubrospinal tract
Ventromedial Group
The vestibulospinal tract, the tectospinal tract, the reticulospinal tract, and the
ventral corticospinal tract
Corticospinal tract
The system of axons that originates in the motor cortex and terminates in the
ventral gray matter of the spinal cord
Pyramidal tract
The portion of the corticospinal tract on the ventral border of the medulla
Lateral corticospinal
tract
The system of axons that originates in the motor cortex and terminates in the
contralateral ventral gray matter of the spinal cord; controls movements of the
distal limbs
Ventral corticospinal
tract
The system of axons that originates in the motor cortex and terminates in the
ipsilateral ventral gray matter of the spinal cord; controls movements of the
upper legs and trunk
Corticobulbar tract
A bundle of axons from the motor cortex to the 5th, 7th, 9th, 10th, 11th, and 12th
cranial nerves; controls movements of the face, neck, tongue, and parts of the
extraocular eye muscles.
Rubrospinal tract
The system of axons that travel form the red nucleus to the spinal cord; controls
independent limb movements
Corticorubral tract
The system of axons that travels from the motor cortex to the red nucleus
Vestibulospinal tract
A bundle of axons that travels from the vestibular nuclei to the gray matter of
the spinal cord; controls postural movements in response to information form
the vestibular system
Tectospinal tract
A bundle of axons that travels from the tectum to the spinal cord; coordinated
head and trunk movements with eye movements
Reticulospinal tract
A bundle of axons that travels from the reticular formation to the gray matter of
the spinal cord; controls the muscles responsible for postural movements.
Mirror neurons
Neurons located in the ventral premotor cortex and inferior parietal lobule that
respond when the individual makes a particular movement or sees another
individual making that movement
Parietal Reach region
A region in the medial posterior parietal cortex that plays a critical role in
control of pointing or reaching with the hands
Apraxia
Difficulty in carrying out purposeful movements, in the absence of paralysis or
muscular weakness
Constructional apraxia
Difficulty in drawing pictures or diagrams or in making geometrical
constructions of element s such as building blocks or sticks; caused by damage
to the right parietal lobe
Caudate nucleus
A telencephalic nucleus, one of the input nuclei of basal ganglia; involved with
control of voluntary movement
Putamen
A telencephalic nucleus, one of the input nuclei of basal ganglia; involved with
control of voluntary movement
Globus pallidus
A telencephalic nucleus; the primary output nucleus of the basal ganglia;
involved with control of voluntary movement
Ventral anterior nucleus
(of thalamus)
A thalamic nucleus that receives projections form the basal ganglia and sends
projections to the motor cortex
Ventrolateral nucleus
(of the thalamus)
A thalamic nucleus that receives projections form the basal ganglia and sends
projections to the motor cortex
Direct pathway (in basal The pathway that includes the caudate nucleus and putamen, the external
ganglia)
division of the globus pallidus, the subthalamic nucleus, the internal division of
the globus pallidus and the VA/VL thalamic nuclei; has an inhibitory effect o
movement
Indirect pathway (in
basal ganglia)
The pathway that includes the caudate nucleus and putamen, the internal
division of the globus pallidus, and the VA/VL thalamic nuclei; has an
excitatory effect o movement
Huntington’s disease
A fatal inherited disorder that causes degeneration of the caudate nucleus and
putamen; characterized by uncontrollable jerking movement, writhing
movements, and dementia
Flocculonodular lobe
A region of the cerebellum; involved in control of posturela reflexes
Vermis
The portion of the cerebellum located at the midline; receives somatosensory
information and helps to control the vestibulospinal and reticulospinal tracts
though its connections with the fastigial nucleus
Fastgial nucleus
A deep cerebellar nucleus; involved in the control of movement by the
reticulospinal and vestibulospinal tracts
Interposed nuclei
A set of deep cerebellar nuclei; involved in the control of the rebrospinal
system
Pontine nucleus
A large nucleus in the pons that serves as an important source of input to the
cerebellum
Denate nucleus
A deep cerebellar nucleus; involved in the control of rapid, skilled movements
by the corticospinal and rubrospinal systems
Mesencephalic
locomotor region
A region of the reticular formation of the midbrain whose stimulation causes
alternating movements of the limbs normally seen during locomotion