Download Slide 1

Neurons and the Brain
3/21-23/05
Next Test:Neurons, Emotions and
Beyond
•
•
•
•
•
•
•
Jansen’s lecture notes
Bedell’s notes and handout
Jacobson’s lecture notes
Reading on emotions
Clark Reading
TEST: 4/12
Presentations: 4/14; 4/19; 4/21; 4/26
Individualism
• And its consequences:
• Discussion: Why isn’t a memory just in
your head?
•
The nervous system is the information highway of the body. It consists of the central and
peripheral nervous systems. The central nervous system is composed of the brain and the
spinal cord. The peripheral nervous system is made up of neurons and nerve endings. The
neuron is the basic unit and messenger of the peripheral nervous system. It is composed
of dendrites, a cell body, an axon and axon terminals. When a nerve signal is sent by the
nervous system, the dendrites receive the signal. The axon then transmits the nerve signal
to the axon terminals which synapse with dendrites or other tissues such as a muscle.
•
There are two types of axons, myelinated and unmyelinated. Unlike unmyelinated axons,
myelinated axons have a sheath of fatty tissue called myelin wrapped around them. There
are breaks in the myelin called Nodes of Ranviers which allow the nerve signal to jump
from node to node. This causes the nerve signal to be transmitted faster.
•
•
•
The Nerve Action Potential
Nerve action potentials are the electrical signals sent out by the body to control bodily processes such as muscular movement.
They are controlled by ions and their concentrations around the nerve cell. They propagate uniformly along the nerve cell and
are governed by the all-or-none phenomena. This means that a nerve action potential will not occur unless the depolarization
threshold is met. The depolarization threshold is the potential that must be reached before depolarization of the nerve cell will
occur. As a nerve action potential propagates along a neuron it goes through several phases which are shown in the graph
below.
•
•
where
(A) Resting state = the membrane potential at rest(before the nerve action potential occurs)
(B) Depolarization = occurs when there is a drastic reversal in membrane potential
(C) Repolarization = occurs when the membrane potential is returning to the resting state
(D) Undershoot = occurs because the potassium gate stays open too long
The Role of Ions
•
The concentration of ions around the nerve cell controls the action potential.
There are two ions that are essential to a normal action potential. These ions
are Sodium (Na+) and Potassium (K+). The Depolarization phase is controlled
by Sodium. An external stimulus causes an influx of Sodium in the nerve cell.
This depolarization, or action potential continues down the neural pathway,
until it reaches its destination. After the cell depolarizes, it must repolarize to
its resting potential before it can depolarize again. This repolarization phase is
controlled by Potassium. An efflux of Potassium causes the potential to return
to its resting state.
The influx of Sodium ions and the efflux of Potassium ions are controlled by
protein gates in the plasma membrane. The influx and efflux of these ions
occurs by diffusion. Diffusion is the process by which ions move from an area
of higher concentration to lower concentration. For example, after the nerve
cell has been stimulated by an external stimulus, an influx of Sodium occurs
because the extracellular concentration is higher than that of the intracellular.
The Sodium-Potassium Pump is a separate protein channel that replenishes
the extracellular environment with Sodium, and the intracellular environment
with Potassium. This protects the extracellular environment from becoming
saturated with Potassium and the intracellular with sodium.
signals
Camillo Golgi
•
Biographical Sketch and Scientific Work
•
Camillo Golgi was born in July 1843 in Corteno, a village in the mountains near Brescia in
northern Italy, where his father was working as a district medical officer. He studied medicine at
the University of Pavia, where he attended as an 'intern student' the Institute of Psychiatry
directed by Cesare Lombroso (1835-1909). Golgi also worked in the laboratory of experimental
pathology directed by Giulio Bizzozero (1846-1901), a brilliant young professor of histology and
pathology (among his several contributions, Bizzozero discovered the hemopoietic properties of
bone marrow). Bizzozero introduced Golgi to experimental research and histological techniques,
and established with him a lifelong friendship. Golgi graduated in 1865 and was, therefore, a
student during the last years of the fights for the independence of Italy (Italy became a united
nation in 1870). Seated left to right: Perroncito, Kölliker, Fusari
In 1872, due to financial problems, Golgi had to interrupt his academic commitment, and
accepted the post of Chief Medical Officer at the Hospital of Chronically Ill (Pio Luogo degli
lncurabili) in Abbiategrasso (close to Pavia and Milan). In the seclusion of this hospital, he
transformed a little kitchen into a rudimentary laboratory, and continued his search for a new
staining technique for the nervous tissue. In 1873 he published a short note ('On the structure of
the brain grey matter') in the Gazzetta Medica Italiana, in which he described that he could
observe the elements of the nervous tissue "studying metallic impregnations... after a long series
of attempts". This was the discovery of the 'black reaction' (reazione nera), based on nervous
tissue hardening in potassium bichromate and impregnation with silver nitrate. Such revolutionary
staining, which is still in use nowadays and is named after him (Golgi staining or Golgi
impregnation) impregnates a limited number of neurons at random (for reasons that are still
mysterious), and permitted for the first time a clear visualization of a nerve cell body with all its
processes in its entirety.
Golgi
Hippocampus
Hippocampus
• hippocampus: means "sea horse", and is named for its
shape. It is one of the oldest parts of the brain, and is
buried deep inside, within the limbic lobe. The
hippocampus is important for the forming, and perhaps
long-term storage, of associative and episodic
memories. Specifically, the hippocampus has been
implicated in (among other things) the encoding of facename associations, the retrieval of face-name
associations, the encoding of events, the recall of
personal memories in response to smells. It may also be
involved in the processes by which memories are
consolidated during sleep.
Santiago Ramon y Cajal
•
•
•
•
Cajal turned all his efforts to improving the silver nitrate technique. As Golgi
had developed it, the staining involved including soaking the tissue in various
substances. Cajal added several levels of preparation and made other
refinements as the debate over the true structure of the central nervous system
was intensifying. While no one had yet seen an entire nerve cell, or could tell
whether it was independent or just part of a larger structure, some scientists
already questioned the old "single network" theory. Fridtjof Nansen, better
known today for his Arctic explorations, had joine several others in theorizing
that nerve cells were independent, basic structures. Still, almost everyone else,
including Golgi and Cajal, believed in the network structure.
In 1887, Cajal became chair of Normal and Pathological Histology at the
university in Barcelona. His most consuming work, however, was slicing,
soaking, staining and affixing to glass slides, slivers of the cerebellum of the
embryo of a small bird. Then he carefully drew what he saw under the
microscope. He became an ardent convert to the independent-cell camp. In
1889, he was invited to show his drawings to the Congress of the German
Anatomical Society at the University of Berlin. It could easily have been a
disaster.
The "short, powerfully built Spaniard with penetrating black eyes set up a
small exhibit of drawings done on paper with colored inks," Everdell writes,
reconstructing the scene. Cajal had explanatory papers delivered to the
German scientists in advance, but few who tried to read them knew any
Spanish. Cajal delivered his speech in fractured French, but still won his case
on the strength of his drawings and slides.
"Each stained cell stood out perfectly against a background of staggering
complexity," writes Everdell, "and no matter how many times the tiny fibers of
one nerve cell met those of another, there was clearly no physical connection
between them. The basic unit of the brain–the neuron–had been isolated." To
this day, Cajal’s meticulous drawings are a defining fixture in neuroscience
texts.
The Nobel and Beyond
• In 1906, Cajal and Golgi shared a Nobel Prize for medicine. The two
met for the first time in Stockholm, and while Cajal was tactful about
sharing the prize, the two still disagreed about the structure of the
brain. Golgi’s speech attacked Cajal’s concept of the independent
neuron, while Cajal’s speech the next day defended it.
• Cajal continued his research, introducing four major new
hypotheses, three of which are now accepted by neuroscientists. He
died in Madrid in 1934
The Nervous Sytems
Structure of the Nervous system
•
1. Central Nervous system (red)
1. Brain
2. Spinal Cord
•
2. Peripheral Nervous System (blue)
1. Somatic
1. sensory-afferents from skin/muscle
2. motor-efferents controlling
movement
2. Autonomic
1. sympathetic- Active in emergency
"fight or flight" reactions
2. Parasympathetic-dominant in
functions related to life maintenance
(eating, storage of fuels)
Medial Saggital View
Coronal Section
Mid-Brain/MRI
•
The brain is surrounded and protected
by the rigid, bony skull and three
membranes, or meninges. The tough,
fibrous outer membrane is the dura
mater. The intermediate membrane,
named the arachnoid, is thin and
weblike. The pia mater is the
innermost covering and is the most
delicate. It is molded to the shape of
the brain. The cerebrospinal fluid
(CSF) surrounds the brain and spinal
cord and flows through open
chambers in the brain, known as
ventricles, and out an opening to the
spinal cord. The brain actually floats in
the shock-absorbing CSF, and is thus
protected from trauma. The CSF also
brings nutrients to the brain and
removes wastes.
Gyrus and Sulcus
• gyrus: a fold or convolution in the cerebrum
• Sulcus: a cleft or fissure in the cerebrum
Central Sulcus
Brain Development
•
The brain develops, in utero, in three
separate portions, reflecting
evolutionary history: the hindbrain, the
midbrain, and the forebrain.
•
•
•
•
The bottom-most part of the brain is the
brain stem. The brain stem is attached to the
spinal cord. It relays information between
parts of the brain or between the brain and
body and regulates basic body function. It is
made up of the midbrain, medulla and the
pons.
Midbrain: The midbrain contains the major
motor supply to the muscles controlling eye
movements and relays information for some
visual and auditory reflexes.
Pons: The pons is a mass of nerve fibers
that serves as a bridge between the medulla
and midbrain above it. The pons is
associated with face sensation and
movement.
Medulla: The medulla (also known as the
medulla oblongata) is located at the base of
the brain stem and controls many of the
mechanisms necessary for life, such as
heartbeat, blood pressure and breathing.
Hindbrain
•
The hindbrain (the oldest part of the brain) develops into the cerebellum, the
pons and the medulla.
• The outermost and top
layer of the brain is the
cerebral cortex. The
cerebral cortex is the
most recently evolved
and most complex part of
the brain. As one moves
lower into the brain, the
parts have increasingly
primitive and basic
functions and are less
likely to require conscious
control.
Cerebellum
• At the back of the head, in between the brain stem and
cerebral cortex, is the cerebellum. The cerebellum
controls balance and coordination and is where learned
movements are stored. Purkinje neurons that control the
refinement of motor movements are found in the
cerebellum. The cerebellum receives input from many
parts of the brain regarding pressure on the limbs, limb
movement, and the position of the limbs in space. The
dentate nucleus, located within the cerebellum,
coordinates skilled movement. Damage to this region, as
a result of HD, causes movements that were once
smooth and refined to become jerky. Movements must
also be constantly relearned.
Lobes
Frontal lobe
•
•
•
•
Frontal Lobe - Front part of the brain;
involved in planning, organizing,
problem solving, selective attention,
personality and a variety of "higher
cognitive functions" including behavior
and emotions.
The anterior (front) portion of the
frontal lobe is called the prefrontal
cortex. It is very important for the
"higher cognitive functions" and the
determination of the personality.
The posterior (back) of the frontal lobe
consists of the premotor and motor
areas. Nerve cells that produce
movement are located in the motor
areas. The premotor areas serve to
modify movements.
The frontal lobe is divided from the
parietal lobe by the central culcus.
Others
•
•
•
•
•
•
•
•
•
Occipital Lobe - Region in the back of the brain which processes visual information. Not only is
the occipital lobe mainly responsible for visual reception, it also contains association areas that
help in the visual recognition of shapes and colors. Damage to this lobe can cause visual deficits.
Parietal Lobe - One of the two parietal lobes of the brain located behind the frontal lobe at the top
of the brain.
Parietal Lobe, Right - Damage to this area can cause visuo-spatial deficits (e.g., the patient may
have difficulty finding their way around new, or even familiar, places).
Parietal Lobe, Left - Damage to this area may disrupt a patient's ability to understand spoken
and/or written language.
The parietal lobes contain the primary sensory cortex which controls sensation (touch, pressure).
Behind the primary sensory cortex is a large association area that controls fine sensation
(judgment of texture, weight, size, shape).
Temporal Lobe - There are two temporal lobes, one on each side of the brain located at about the
level of the ears. These lobes allow a person to tell one smell from another and one sound from
another. They also help in sorting new information and are believed to be responsible for shortterm memory.
Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and faces).
Left Lobe - Mainly involved in verbal memory (i.e., memory for words and names).
• Brodmann’s Areas
Studies done by Brodmann in the early part of the twentieth century
generated a map of the cortex covering the lobes of each
hemisphere. These studies involved electrical probing of the
cortices of epileptic patients during surgery. Brodmann
numbered the areas that he studies in each lobe and recorded
the psychological and behavioral events that accompanied
their stimulation.
The Frontal Lobe contains areas that Brodmann identified as
involved in cognitive functioning and in speech and language.
Area 4 corresponds to the precentral gyrus or primary motor area.
Area 6 is the premotor or supplemental motor area.
Area 8 is anterior of the premotor cortex. It facilitates eye
movements and is involved in visual reflexes as well as pupil
dilation and constriction.
Areas 9, 10, and 11 are anterior to area 8. They are involved in
cognitive processes like reasoning and judgement which may
be collectively called biological intelligence.
Area 44 is Broca's area.
Areas in the Parietal Lobe play a role in somatosensory processes.
Areas 3, 2, and 1 are located on the primary sensory strip, with area
3 being superior to the other two. These are somastosthetic
areas, meaning that they are the primary sensory areas for
touch and kinesthesia.
Areas 5, 7, and 40 are found posterior to the primary sensory strip
and correspond to the presensory to sensory association
areas.
Area 39 is the angular gyrus.
Areas involved in the processing of auditory information and
semantics as well as the appreciation of smell are found in the
Temporal Lobe.
Area 41 is Heschl's gyrus, or the primary auditory area.
Area 42 immediately inferior to area 41 and is also involved in the
detection and recognition of speech. The processing done in
this area of the cortex provides a more detailed analysis than
that done in area 41.
Areas 21 and 22 are the auditory association areas. Both areas are
divided into two parts; one half of each area lies on either side
of area 42.
Area 37 is found on the posterior-inferior part of the temporal lobe.
Lesions here will cause anomia.
The Occipital Lobe contains areas that process visual stimuli.
Area 17 is the primary visual area.
Areas 18 and 19 are the secondary visual areas.
Limbic System
http://www2.umdnj.edu/~neuro/studyaid/Practical2000/practical2000.htm
Rods and Cones
• two kinds of photoreceptors of vertebrate
eyes
• rods very light sensitive, and sensitive to
wider range of wavelengths, useful at night
and under low light conditions, incapable of
wavelength discrimination
• in moderate light, both rods and cones
contribute to vision, at high light levels, rods
saturate
• cones useful in higher light conditions,
populations with differing wavelength
sensitivity form basis for color vision
The LGN
• Optic nerve fibres from
the eyes terminate at two
bodies in the thalamus (a
structure in the middle of
the brain) known as the
Lateral Geniculate Nuclei
(or LGN for short). One
LGN lies in the left
hemisphere and the other
lies in the right
hemisphere.
Visual System
Areas of the Visual Cortex
Macque Monkey VS
The binding problem
• Visual information processing takes place in
parallel with different areas processing
different image attributes. How does brain
keep track of how these attributes relate to
one another? Our phenomenal experience is
of a singular unitary visual world, how does
this relate to the multiple visual maps of our
brain?
LOLA