Download Chapter 2: Brain and Behavior

Chapter 2
Brain and Behavior
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Neuron and Its Parts
Neuron: Individual nerve cell; 100 billion in
brain
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Dendrites: Receive messages from other neurons
Soma: Cell body; body of the neuron. Receives
messages and sends messages down axon
Axon: Carries information away from the cell body
Axon Terminals: Branches that link the dendrites
and somas of other neurons
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Fig. 2.1 An example of
a neuron, or nerve
cell, showing several
of its important
features. The right
foreground shows a
nerve cell fiber in
cross section, and the
upper left inset gives a
more realistic picture
of the shape of
neurons. The nerve
impulse usually travels
from the dendrites and
soma to the branching
ends of the axon. The
neuron shown here is
a motor neuron. Motor
neurons originate in
the brain or spinal
cord and send their
axons to the muscles
or glands of the body.
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Fig. 2.2 Activity in an axon can be measured by placing electrical probes inside and outside the axon. (The
scale is exaggerated here. Such measurements require ultra-small electrodes, as described later in this
chapter.) At rest, the inside of an axon is about –60 to –70 millivolts, compared with the outside.
Electrochemical changes in a nerve cell generate an action potential. When positively charged sodium ions
(Na+) rush into the cell, its interior briefly becomes positive. This is the action potential. After the action
potential, an outward flow of positive potassium ions (K+) restores the negative charge inside the axon.
(See Figure 2.3 for further explanation.)
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Fig. 2.5 A highly magnified view of the synapse shown in Fig. 2.1. Neurotransmitters are stored in tiny
sacs called synaptic vesicles. When a nerve impulse arrives at an axon terminal, the vesicles move to the
surface and release neurotransmitters. These transmitter molecules cross the synaptic gap to affect the
next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch.
Transmitter molecules vary in their effects: Some excite the next neuron and some inhibit its activity.
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The Nerve Impulse
Resting Potential: Electrical charge of an
inactive neuron
Threshold: Trigger point for a neuron’s firing
Action Potential: Nerve impulse
Ion Channels: Axon membrane has these tiny
holes or tunnels
Negative After-Potential: When a neuron is
less willing to fire
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Fig. 2.3 The inside of an axon normally has a negative electrical charge. The fluid surrounding an axon is
normally positive. As an action potential passes along the axon, these charges reverse, so that the
interior of the axon briefly becomes positive.
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Fig. 2.4 Cross-sectional
views of an axon. The right
end of the top axon is at rest,
with a negatively charged
interior. An action potential
begins when the ion
channels open and sodium
ions (Na+) enter the axon. In
this drawing the action
potential would travel rapidly
along the axon, from left to
right. In the lower axon the
action potential has moved to
the right. After it passes,
potassium ions (K+) flow out
of the axon. This quickly
renews the negative charge
inside the axon, so it can fire
again. Sodium ions that enter
the axon during an action
potential are pumped back
out more slowly. Their
removal restores the original
resting potential.
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Animation: Neuron & Neural
Impulse
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Neurotransmitters
Chemicals that alter activity in neurons; brain
chemicals
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Acetylcholine: Activates muscles
Dopamine: Muscle control
Serotonin: Mood and appetite control
Messages from one neuron to another pass
over a microscopic gap called a synapse
Receptor Site: Areas on the surface of
neurons and other cells that are sensitive to
neurotransmitters
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Animation: Synaptic
Transmission
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Neural Regulators
Neuropeptides: Regulate activity of
other neurons
Enkephalins: Relieve pain and stress;
similar to endorphins
 Endorphins: Released by pituitary gland;
also help to relieve pain
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Placebos raise endorphin levels
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Nerves and Neurons
Nerves: Large bundles of axons and
dendrites
Myelin: Fatty layer that coats some axons
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Multiple Sclerosis (MS) occurs when myelin layer
is destroyed; numbness, weakness, and paralysis
occur
Neurilemma: Thin layer of cells wrapped
around axons outside brain and spinal cord;
forms a tunnel that damaged fibers follow as
they repair themselves
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Neural Networks
Central Nervous System (CNS): Brain and
spinal cord
Peripheral Nervous System: All parts of the
nervous system outside of the brain and
spinal cord
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Somatic System: Carries messages to and from
skeletal muscles and sense organs; controls
voluntary behavior
Autonomic System: Serves internal organs and
glands; controls automatic functions such as heart
rate and blood pressure
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Two Divisions of the Autonomic
System
Sympathetic: Arouses body; emergency
system
Parasympathetic: Quiets body; most
active after an emotional event
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Fig. 2.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic
nervous system.
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Fig. 2.7 Subparts of the nervous system.
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Fig. 2.8 Sympathetic
and parasympathetic
branches of the
autonomic nervous
system.
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Fig. 2.9 A simple sensorymotor (reflex) arc. A simple
reflex is set in motion by a
stimulus to the skin (or other
part of the body). The nerve
impulse travels to the spinal
cord and then back out to a
muscle, which contracts.
Reflexes provide an
“automatic” protective device
for the body.
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The Spinal Cord
Spinal Nerves: 31 of them; carry
sensory and motor messages to and
from the spinal cord
Cranial Nerves: 12 pairs that leave the
brain directly; also work to communicate
messages
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How is the Spinal Cord Related
to Behavior?
Reflex Arc: Simplest behavioral pattern; occurs when
a stimulus provokes an automatic response
Sensory Neuron: Nerve cell that carries messages
from the senses toward the CNS
Connector Neuron: Nerve cell that links two others
Motor Neuron: Cell that carries commands from the
CNS to muscles and glands
Effector Cells: Cells capable of producing a response
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Researching the Brain
Ablation: Surgical removal of parts of the brain
Deep Lesioning: A thin wire electrode is lowered into
a specific area inside the brain; Electrical current is
then used to destroy a small amount of brain tissue
Electrical Stimulation of the Brain (ESB): When an
electrode is used to activate target areas in the brain
Electroencephalograph (EEG): Detects, amplifies,
and records electrical activity in the brain
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Fig. 2.10 The functions of brain structures are explored by selectively activating or removing them. Brain
research is often based on electrical stimulation, but chemical stimulation is also used at times.
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Fig. 2.11 An EEG recording.
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Researching the Brain (cont.)
Computed Tomographic Scanning (CT): Computerenhanced X-ray of the brain or body
Magnetic Resonance Imaging (MRI): Uses a strong
magnetic field, not an X-ray, to produce an image of
the body’s interior
Functional MRI: MRI that makes brain activity visible
Positron Emission Tomography (PET): Computergenerated color image of brain activity, based on
glucose consumption in the brain
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© Huntington Magnetic Resonance Center, Pasadena, California
Fig. 2.12 An MRI scan of the brain.
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Washington University School of Medicine, St.
Fig. 2.13 PET scans.
Louis
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Washington University School of Medicine, St. Louis
Fig. 2.14 The bright spots you see here were created by a PET scan. They are similar to the spots in
Figure 2.13. However, here they have been placed over an MRI scan so that the brain’s anatomy is visible.
The three bright spots are areas in the left brain related to language. The spot on the right is active during
reading. The top-middle area is connected with speech. The area to the left, in the frontal lobe is linked
with thinking about a word’s meaning (Montgomery, 1989).
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Courtesy of Richard Haier, University of California, Irvine
Fig. 2.16 In the images you see here, red, orange, and yellow indicate high consumption of glucose;
green, blue, and pink show areas of low glucose use. The PET scan of the brain on the left shows that a
man who solved 11 out of 36 reasoning problems burned more glucose than the man on the right, who
solved 33.
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CNN – Brain Mapping
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Cerebral Cortex
Definition: Outer layer of the cerebrum;
contains 70% of neurons in CNS
Cerebrum: Two large hemispheres that cover
upper part of the brain
Corticalization: Increase in size and wrinkling
of the cortex
Cerebral Hemispheres: Right and left halves
of the cerebrum
Corpus Callosum: Bundle of fibers connecting
cerebral hemispheres
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Split Brains
Corpus Callosum is cut; done to control
severe epilepsy (seizure disorder)
Result: The person now has two brains
in one body
This operation is rare and is often used
as a last resort
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Figure 2.17 Corpus Callosum
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Fig. 2.19 Basic nerve
pathways of vision. Notice
that the left portion of each
eye connects only to the left
half of the brain; likewise, the
right portion of each eye
connects to the right brain.
When the corpus callosum is
cut, a “split brain” results.
Then visual information can
be directed to one
hemisphere or the other by
flashing it in the right or left
visual field as the person
stares straight ahead.
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Right Brain/Left Brain
About 95 percent of our left brain is used for
language
Left hemisphere better at math, judging time and
rhythm, and coordinating order of complex
movements
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Processes information sequentially and is involved with
analysis
Right hemisphere good at perceptual skills, and at
expressing and detecting other’s emotions
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Processes information simultaneously and holistically
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Fig. 2.20 If a circle is flashed to the left brain and a split-brain patient is asked to say what she or he saw, the
circle is easily named. The person can also pick out the circle by touching shapes with the right hand, out of
sight under a tabletop (shown semi-transparent in the drawing). However, the left hand will be unable to
identify the shape. If a triangle is flashed to the right brain, the person cannot say what was seen (speech is
controlled by the left hemisphere). The person will also be unable to identify the correct shape by touch with
the right hand. Now, however, the left hand will have no difficulty picking out the hidden triangle. Separate
testing of each hemisphere reveals distinct specializations, as listed above.
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Central Cortex Lobes
Occipital: Back of brain; vision center
Parietal: Just above occipital; bodily
sensations such as touch, pain, and
temperature (somatosensory area)
Temporal: Each side of the brain; auditory
and language centers
Frontal: Movement, sense of smell, higher
mental functions
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Contains motor cortex; controls motor movement
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Fig. 2.21 The left
and right brain
have different
information
processing styles.
The right brain gets
the big pattern; the
left focuses on
small details.
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When the Brain Fails to Function
Properly
Association Cortex: Combine and process information
from the five senses
Aphasia: Language disturbance resulting from brain
damage
Broca’s Area: Related to language and speech
production
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If damaged, person knows what s/he wants to say but can’t say
the words
Wernicke’s Area: Related to language comprehension;
in left temporal lobe
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If damaged, person has problems with meanings of words, NOT
pronunciation
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When the Brain Fails to Function
Properly (cont.)
Agnosia: Inability to identify seen
objects
Facial Agnosia: Inability to perceive
familiar faces
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CNN – Stroke Brain repair
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Subcortex
Immediately below cerebral hemispheres
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Hindbrain (Brainstem): Consists mainly of medulla
and cerebellum
Medulla: Controls vital life functions such as heart
rate, swallowing, and breathing
Pons (Bridge): Acts as a bridge between medulla
and other structures
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Influences sleep and arousal
Cerebellum: Located at base of brain
Regulates posture, muscle tone, and muscular
coordination
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Fig. 2.25 This simplified drawing shows the main structures of the human brain and describes some of their
most important features. (You can use the color code in the foreground to identify which areas are part of the
forebrain, midbrain, and hindbrain.)
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Subcortex: Reticular Formation
(RF)
Reticular Formation: Inside medulla and
brainstem
Associated with alertness, attention, and
some reflexes (breathing, coughing,
sneezing, vomiting)
 Reticular Activating System (RAS): Part of
RF that keeps it active and alert
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RAS acts like the brain’s alarm clock
 Activates and arouses cerebral cortex
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Forebrain
Structures are part of Limbic System: System
within forebrain closely linked to emotional
response and motivating behavior
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Thalamus: Relays sensory information on the way
to the cortex; switchboard
Hypothalamus: Regulates emotional behaviors
and motives (e.g., sex, hunger, rage, hormone
release)
Amygdala: Associated with fear responses
Hippocampus: Associated with storing permanent
memories; helps us navigate through space
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Endocrine System
Glands that pour chemicals (hormones)
directly into the bloodstream or lymph system
Pituitary Gland: Regulates growth via growth
hormone
Too little means person will be smaller than
average
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Hypopituitary Dwarfs: As adults, perfectly
proportioned but tiny
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Treatable by using human or synthetic growth hormone;
will add a few inches
Treatment is long and expensive
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CNN – Thought Control
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Fig. 2.26 Parts of the
limbic system are
shown in this highly
simplified drawing.
Although only one side
is shown, the
hippocampus and the
amygdala extend out
into the temporal lobes
at each side of the
brain. The limbic
system is a sort of
“primitive core” of the
brain strongly
associated with
emotion.
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Endocrine System (cont.)
Too much growth hormone leads to giantism
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Excessive body growth
Acromegaly: Enlargement of arms, hands,
feet, and facial bones
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Caused by too much growth hormone secreted
late in growth period
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Andre the Giant
Pituitary also governs functioning of other
glands, especially thyroid, adrenals, and
gonads
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Endocrine System (cont.)
Pineal Gland: Regulates body rhythms and
sleep cycles.
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Releases hormone melatonin, which responds to
daily variations in light
Thyroid: In neck; regulates metabolism
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Hyperthyroidism: Overactive thyroid; person tends
to be thin, tense, excitable, nervous
Hypothyroidism: Underactive thyroid; person tends
to be inactive, sleepy, slow, obese
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The Adrenal Glands
Adrenals: Arouse body, regulate salt balance,
adjust body to stress, regulate sexual
functioning; located on top of kidneys
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Releases epinephrine and norepinephrine (also
known as adrenaline and noradrenaline)
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Epinephrine arouses body; is associated with fear
Norepinephrine arouses body; is linked with anger
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The Adrenal Glands (cont.)
Adrenal Medulla: Inner core of adrenals; source of
epinephrine and norepinephrine
Adrenal Cortex: Produces hormones known as
corticoids
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Regulate salt balance
Deficiency in some types will cause powerful salt cravings
Also help body to adjust to stress
Secondary source of sex hormones
Oversecretion of adrenal sex hormones can cause
virilism: exaggerated male characteristics (Bearded
woman)
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May also cause premature puberty if oversecretion occurs early
in life
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Neurogenesis and Plasticity
Neurogenesis: Production of new brain
cells
Plasticity: Brain’s ability to change its
structure and functions
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Fig. 2.31 Neuroscientists are searching for
ways to repair damage caused by strokes and
other brain injuries. One promising technique
involves growing neurons in the laboratory
and injecting them into the brain. These
immature cells are placed near damaged
areas, where they can link up with healthy
neurons. The technique has proved
successful in animals and is now under study
in humans.
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Fig. 2.27 A direct brain-computer link may provide a way of communicating for people who are paralyzed and unable
to speak. Activity in the patient’s motor cortex is detected by an implanted electrode. The signal is then amplified and
transmitted to a nearby computer. By thinking in certain ways, patients can move an on-screen cursor. This allows
them to spell out words or select from a list of messages, such as “I am thirsty.”
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