Transcript The Brain, Biology, and Behavior

Chapter 3
The Brain, Biology, and Behavior
Neuron and its parts
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Neuron: Individual nerve cell
 Dendrites: Receive messages from other neurons
 Soma: Cell body; body of the neuron
 Axon: Carries information away from the cell body
 Axon Terminals: Branches that link the dendrites and soma of
other neurons
Figure 3.1
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.
Figure 3.2
Activity in an axon can be measured by placing electrical probes inside and outside the axonal
membrane. (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 minus 60
to 70 millivolts, compared with the outside. Electrochemical changes in a nerve cell generate
an action potential. When positively charged sodium ions (Na1) 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 (K1) restores the negative charge inside the axon. (See Figure 3.3
for further explanation.)
Figure 3.3
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.
Figure 3.4
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 (Na1)
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 (K1) 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.
Figure 3.5
A highly magnified view of the synapse shown in Fig. 3.1. 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.
The Neuron and Neuronal Impulse
Please choose the button below that corresponds to the type of
operating system you are using:
Neurotransmitters
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Chemicals that alter activity in neurons; brain chemicals. Some
examples:
 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 or hormones
Synaptic Transmission
Please choose the button below that corresponds to the type of
operating system you are using:
Neural Regulators
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Neural Peptides: Regulate activity of other neurons
 Enkephalins: Relieve pain and stress
Neural Networks
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Central Nervous System (CNS): Brain and spinal cord.
Peripheral Nervous System: All parts of the nervous system outside
of the brain and spinal cord.
 Somatic System: Links spinal cord with body and sense organs.
Controls voluntary behavior
 Autonomic System: Serves internal organs and glands.
Controls automatic functions such as heart rate and blood
pressure
 Sympathetic: Arouses body
 Parasympathetic: Quiets body
Figure 3.6
(a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the
autonomic nervous system.
Figure 3.7 Subparts of the nervous system.
Figure 3.8
Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches
control involuntary actions. The sympathetic system generally activates the body. The
parasympathetic system generally quiets it. The sympathetic branch relays through a chain of
ganglia (clusters of cell bodies) outside the spinal cord.
Figure 3.9
A simple sensory-motor (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.
Researching the Brain
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Electroencephalograph (EEG): Detects, amplifies and records
electrical activity in the brain
Computed Tomographic Scanning (CT): Computer-enhanced XRay of the brain or body
Magnetic Resonance Imaging (MRI): Uses a strong magnetic field,
not an X-Ray, to produce an image
Functional MRI: MRI that also records brain activity
Positron Emission Tomography (PET): Computer-generated color
image of brain activity, based on glucose consumption in the brain.
Launch
Video
Cerebral Cortex
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Outer layer of the cerebrum
Cerebrum: Two large hemispheres that cover upper part of the brain
Cerebral Hemispheres: Right and left halves of the cerebrum
Corpus Callosum: Bundle of fibers connecting cerebral hemispheres
Figure 3.15
An illustration showing the increased relative size of the human cerebrum and cerebral cortex,
a significant factor in human adaptability and intelligence.
Figure 3.17
The corpus callosum is the major “cable system” through which the right and left cerebral
hemispheres communicate. A recent study found that the corpus callosum is larger in
classically trained musicians than it is in nonmusicians. When a person plays a violin or piano,
the two hemispheres must communicate rapidly as they coordinate the movements of both
hands. Presumably, the size of the corpus callosum can be altered by early experience, such
as musical training.
Central Cortex Lobes
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Occipital: Back of brain; vision center
Parietal: Just above occipital; bodily sensations such as
touch, pain, and temperature
Temporal: Each side of the brain; auditory and language
centers
Frontal: Movement, sense of smell, higher mental functions
 Contains motor cortex; controls motor movement
Figure 3.19
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.
Figure 3.20
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 semitransparent 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. (Figure adapted from an illustration by Edward Kasper
in McKean, 1985.)
Figure 3.22
Many of the lobes of the cerebral cortex are defined by larger fissures on the surface of the
cerebrum. Others are regarded as separate areas because their functions are quite different.
Figure 3.23
The lobes of the
cerebral cortex and
the primary
sensory, motor, and
association areas
on each. The top
diagrams show (in
cross section) the
relative amounts of
cortex “assigned” to
the sensory and
motor control of
various parts of the
body. (Each cross
section, or “slice,”
of the cortex has
been turned 90
degrees so that you
see it as it would
appear from the
back of the brain.)
When the brain fails to function properly
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Aphasia: Speech disturbance resulting from brain damage
Broca’s Area: Related to language and speech production.
 If damaged, person knows what s/he wants to say but
can’t say the words
Wernicke’s Area: Related to language comprehension.
 If damaged, person has problems with meanings of
words, NOT pronunciation
Agnosia: Inability to identify seen objects
Facial agnosia: Inability to perceive familiar faces
Figure 3.28 Language is controlled by the left side of the brain in the majority of right- and lefthanders.
Figure 3.32
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.”
Subcortex
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Hindbrain (brainstem)
 Medulla: Connects brain with the spinal cord and controls
vital life functions such as heart rate and breathing
 Pons (Bridge): Acts as a bridge between brainstem and
other structures.
 Influences sleep and arousal
 Cerebellum: Located at base of brain.
 Regulates posture, muscle tone and muscular
coordination
Subcortex: Reticular Formation (RF)
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Reticular Formation (RF): Inside medulla.
 Associated with alertness, attention and some reflexes
Reticular Activating System (RAS): Part of RF that keeps it
active and alert.
 Its alarm clock
 Activates and arouses cerebral cortex
Forebrain
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Structures are part of Limbic System:
 System within forebrain closely linked to emotional
response
 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 memories
Figure 3.26
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.
Figure 3.25
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.)
Endocrine System
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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
 Too much leads to giantism:
 Excessive body growth
 Acromegaly: Enlargement of arms, hands, feet and
facial bones.
 Too much growth hormone released late in
growth period
 Andre the Giant
Endocrine System Continued
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Pineal Gland: Regulates body rhythms and sleep cycles.
 Releases hormone melatonin, which responds to
variations in light
Thyroid: In neck; regulates metabolism
 Hyperthyroidism: Overactive thyroid; person tends to be
thin, tense, excitable, nervous
 Hypothyroidism; Underactive thyroid; person tends to be
inactive, sleepy, slow, obese
Adrenals: Arouse body, regulate salt balance, adjust body to
stress, regulate sexual functioning
Figure 3.27 Locations of the endocrine glands in the male and female.
Neurogenesis and Plasticity
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Plasticity: Brain’s capacity to change its structure and
functions
Neurogenesis: Production of new brain cells
Figure 3.31
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.