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Transcript
CHAPTER OUTLINE
Biological psychology studies the cells, genes, and organs of the body, and the physical and
chemical changes involved in behavior and mental processes.
I.
CELLS OF THE NERVOUS SYSTEM
What are neurons and what do they do?
A.
B.
C.
D.
Neurons
1. There are two main cell types in the nervous system.
a) Neurons are specialized to respond rapidly to signals and send signals of
their own.
b) Glial cells hold neurons together, guide their growth, maintain a stable
chemical environment, provide energy, help restore damage, and respond
to signals from neurons.
2. All cells have some features in common.
a) An outer membrane selectively allows only some substances to pass in and
out.
b) The cell body contains the nucleus.
c) Mitochondria turn oxygen and glucose into energy.
3. Neurons have special features that permit effective signal communication.
a) An axon is a cell fiber that carries signals away from the cell body. Most
neurons have just one axon.
b) A dendrite is a cell fiber that receives signals from other neurons and
carries information toward the neuron’s cell body. Most neurons have
many dendrites.
Action Potentials
1. Action potentials are electrochemical pulses that shoot down the neuron’s axon.
They are “all-or-none”: A neuron either fires an action potential at full strength
or does not fire at all.
2. After an action potential, there is a brief recovery time called a refractory
period, during which a neuron cannot fire another action potential.
3. The speed of an action potential depends on the thickness of the axon and on the
presence of myelin, a white, fatty substance that speeds up action potentials.
Synapses and Communication Between Neurons
1. At the axon end, the action potential causes baglike vesicles to release stored
chemicals called neurotransmitters into a space between the two neurons.
2. This space is called a synapse, a connection that is a narrow gap separating the
axon of one neuron from the dendrites of another. It is the means by which two
neurons communicate.
3. Released neurotransmitters “float” across the synapse to “bind” with receptors,
proteins on a dendrite of a receiving neuron.
4. The interaction between neurotransmitters and receptors is very specific, like a
lock and key. A specific receptor (a “lock”) can only be stimulated by a specific
neurotransmitter (a “key”).
5. This interaction creates a signal called a postsynaptic potential (PSP) that might
make action potentials in the receiving, or postsynaptic, neuron either more or
less likely. A number of PSPs sum together at the junction of the cell body and
the axon. Whether or not an action potential “fires” depends on the kind of
signals that are most numerous.
Organization of the Nervous System
The nervous system is organized into two main parts:
1. The central nervous system (CNS), encased in bone, consists of the brain and
spinal cord. The CNS is the nervous system’s central executive.
2. The peripheral nervous system extends throughout the body and relays
information to and from the brain.
II.
THE PERIPHERAL NERVOUS SYSTEM: KEEPING IN TOUCH WITH THE WORLD
How do sights and sounds reach my brain?
The peripheral nervous system has two subsystems:
A. The Somatic Nervous System
The somatic nervous system carries signals between the senses and CNS and
between the CNS and skeletal muscles. Sensory neurons bring information to the
brain, and motor neurons send information from the brain to the muscles.
B. The Autonomic Nervous System
The autonomic nervous system (ANS) carries messages between the CNS and the
heart, lungs, and other organs and glands. The ANS has two divisions:
1. The sympathetic system directs the body to spend energy (e.g., increased heart
rate, faster breathing, sweating; sometimes called the “fight-or-flight” response)
to react to stress.
2. The parasympathetic system directs the body’s functions to conserve energy
(e.g., slower heart rate, increased digestive activity). Parasympathetic activity
helps “calm” a person after increased sympathetic arousal.
3. Both systems may act on the same body areas, with their relative “balance”
regulating the state of the targeted organs.
III. THE CENTRAL NERVOUS SYSTEM: MAKING SENSE OF THE WORLD
How is my brain "wired"?
In the CNS different functions are performed by different networks of neurons. Clusters of
neurons are called nuclei, and pathways that connect the networks are bundles of axons
called fiber tracts.
A.
B.
The Spinal Cord
The spinal cord receives and sends signals to and from the brain.
1. Reflexes are simple, involuntary behaviors controlled by spinal cord neurons,
without requiring instructions from the brain.
2. Reflexes are controlled by a feedback system. Information about the
consequences of an action goes back to the source of the action for further
adjustment, if necessary.
The Brain
A number of tools have been developed for monitoring the brain’s structure and
activity:
1. The earliest technique is called an electroencephalogram (EEG), which
measures general electrical activity through electrodes on the scalp.
2. A newer technique is a positron emission tomography (PET) scan, which records
the location of radioactive substances that were injected into the bloodstream.
These show the location of brain activity during specific tasks.
3. Magnetic resonance imaging (MRI) records radio frequency waves after
exposure to a magnetic field providing clear pictures of the anatomical structure
of the brain.
4. Functional MRI (fMRI) detects changes in blood flow to provide a “moving
picture” of neuronal activities.
5.
C.
D.
The newest techniques provide even more information about brain activity,
structure, and functioning. These include diffusion tensor imaging (DTI) and
transcranial magnetic stimulation (TMS).
Thinking Critically: What Can fMRI Tell Us about Behavior and Mental Processes?
fMRI scans show where brain activity occurs as people think and experience emotion.
Like phrenology in the nineteenth century, which claimed that personality traits and
other mental features could be determined from bumps on people’s skulls, some feel
that people will uncritically accept the claim that fMRI scans also indicate how the
mind works.
1.
What am I being asked to believe or accept?
fMRI scans cannot indicate the anatomical locations—in other words, the
biological causes—of particular thoughts and emotions.
2.
Is there evidence available to support the claim?
Although brain areas do “light up” when a person thinks or feels something,
fMRI scans of these areas are not precise. First, they do not directly measure
brain cell activities but just reflect blood flow and oxygen in the brain that are
related in some unknown way to neuron firings. Second, an fMRI scan may miss
brain cell activities that do not create simple increases in blood flow. Third,
coordinated changes in millions of neurons are necessary before a detectable
fMRI signal occurs. Fourth, many of the results of fMRI research depend on how
the researchers decide to interpret them—they depend on judgments. And,
finally, no one knows what it really means when certain brain areas appear to be
activated during certain experiences.
3.
Can that evidence be interpreted another way?
Supporters point to important fMRI research on brain mechanisms involved with
experiencing empathy and learning by watching others. Mirror neuron
mechanisms were found in parts of the brain including Broca’s area. Neurons in
these areas become activated not only when a person actually experiences
something, but also when he/she watches someone else do or feel the same thing.
Some fMRI studies have found malfunctioning mirror mechanisms in people
diagnosed with autism, a disorder that includes problems with language
development, imitative skills, and empathy.
4.
What evidence would help to evaluate the alternatives?
The fMRI technology will continue to improve, but knowledge about correlation
and causation in fMRI must also grow. Transcranial magnetic stimulation
(TMS) procedures might help identify causal versus correlational relationships in
the brain by temporarily disrupting neural activity in brain regions identified by
fMRI as related to a particular kind of thought or feeling. Sharing information
from fMRI experiments will help to better interpret the available data. An fMRI
data center has been established to store research data for review.
5.
What conclusions are most reasonable?
The fMRI is an exciting tool that offers images of the structure and functioning
of the brain. However, by itself, fMRI probably will not be able to explain
exactly how the brain creates behavior and mental processes. Critical thinking
must always underlie analysis of results of fMRI research.
The Hindbrain
The hindbrain is found just above the spinal cord and is composed of the following
structures:
1.
E.
F.
G.
H.
The medulla controls vital life functions (e.g., blood pressure, heart rate,
breathing).
2. The reticular formation is a web of neurons involved in arousal and attention.
3. The locus coeruleus is a small nucleus within the reticular formation involved in
directing attention.
4. The cerebellum coordinates fine motor movements, stores a memory code for
well-rehearsed behaviors, and participates in cognitive tasks such as reading.
The Midbrain
The tiny midbrain relays information from the eyes, ears, and skin and controls
certain types of automatic behaviors. The midbrain and its connections to the forebrain
permit the smooth initiation of movement.
The Forebrain
The forebrain, the largest part of the brain, regulates many complex aspects of
behavior and mental phenomena. Interior structures include the following:
1. The thalamus processes inputs from sense organs (except for smell) and then
relays sensory information to appropriate “higher” forebrain areas. It is the
primary sensory relay into the rest of the brain.
2. The hypothalamus regulates many physiological feedback systems,
coordinating hunger, thirst, temperature regulation, and sexual behavior. It
directly influences both the autonomic and the endocrine systems. It contains the
suprachiasmatic nuclei, the brain’s “clock” that sets biological rhythms for the
body.
3. The limbic system includes the amygdala and the hippocampus.
a) The amygdala is involved in memory and emotion. It links different kinds
of sensory information together in memory. The amygdala also plays a
role in fear and other emotions, linking emotions to sensations.
b) The hippocampus is critical to the ability to form new memories.
The Cerebral Cortex
1. The forebrain’s outer surface, the cerebral cortex, is a thin sheet of neurons. In
humans, the sheet folds in on itself, giving the brain its characteristic wrinkled
appearance.
2. The cerebral cortex is divided down the middle, creating two halves called the
left and right cerebral hemispheres. The corpus callosum connects the two
halves.
3. The folds of cortex produce gyri (ridges) and sulci, or fissures (valleys or
wrinkles), on the brain’s outer surface. Several deep sulci make convenient
markers for dividing the cortex of each hemisphere into four anatomical areas:
the frontal, parietal, occipital, and temporal lobes.
Sensory and Motor Cortex
The sensory cortex and the motor cortex are two of the functional areas of the cortex.
1. Each region of the sensory cortex receives and processes input from a single
sensory organ.
a) Inputs from the eyes are sent to the visual cortex in the occipital lobe.
b) Inputs from the ears are sent to the auditory cortex in the temporal lobe.
c) Inputs from the skin sensory organs connect to the somatosensory cortex in
the parietal lobe. Information about skin sensations from neighboring parts
of the body comes to neighboring parts of the somatosensory cortex.. This
pattern on the somatosensory cortex is called a homunculus, because it is an
outline of an upside-down little person.
2.
I.
J.
K.
Neurons in the motor cortex, in the frontal lobe, initiate voluntary movements of
specific body parts. These neurons are organized so that the combined activity of
neighboring groups of neurons controls movements of neighboring body regions.
Focus on Research: The Case of the Disembodied Woman
1. What was the researcher’s question?
Why was an apparently healthy woman falling and dropping things?
2. How did the researcher answer the question?
Dr. Sacks conducted a case study of Christina to check her sensory feedback
from her joints and muscles.
3. What did the researcher find?
Christina’s sensory neurons that usually supply kinesthetic information had
stopped working.
4. What do the results mean?
Our sense of our bodies comes not just from seeing them, but also from
proprioception.
5. What do we still need to know?
Dr. Sack’s research provided detailed information on what neurological problem
Christina experienced, but it did not show what caused her condition. Did
megadoses of vitamin B6 contribute to Christina’s problem and, if so, why? Are
there other causes of this kinesthetic disorder?
Association Cortex
1. Most of the cortex in each lobe is association cortex, with no specific sensory
inputs or direct motor outputs. Rather, the association cortex combines inputs
from various senses and is involved in many different mental processes.
a) Some regions of the association cortex are specifically involved in
language processing.
(1) Broca’s area is a region of association cortex, usually in the left
frontal lobe. Damage to this region causes difficulty speaking
smoothly and grammatically, a condition called Broca’s aphasia.
(2) Wernicke’s area is a region of the association cortex, usually in the
left temporal lobe. Damage to this region leaves fluency intact but
makes it difficult to understand the meaning of words or to speak
understandably.
b) Other association areas in the front of the brain called the prefrontal cortex
are involved in complex, higher-level thought processes.
The Divided Brain: Lateralization
1. The physically separate left and right hemispheres perform different functions.
2. Most sensory and motor pathways cross as they enter or leave the brain. As a
result, the left hemisphere receives information from and controls movements of
the right side of the body, and the right hemisphere does the same for the left
side of the body.
3. Studies of split-brain patients highlight the different functions of the two
hemispheres.
a) The left and right hemispheres communicate through the corpus callosum,
a bundle of over a million fibers. To relieve seizures in some epilepsy
patients, a “split-brain” operation cuts the corpus callosum. In such
patients, the two hemispheres operate somewhat independently of each
other.
b) Special techniques were used to present information to only the left or right
hemisphere of split brains. Patients could verbally name only those objects
shown to the left hemisphere; they could use their hands to recognize
objects shown to either hemisphere. This suggested that the left
hemisphere, more than the right, is specialized for language.
c) The right hemisphere appears to be specialized for tasks involving spatial
relationships and recognizing human faces.
d) Because of the corpus callosum connection, the two hemispheres work
closely together.
L. Plasticity in the Central Nervous System
1. Brains show neural plasticity, adding or changing synapses due to one’s
experiences. This is a physical basis for forming memories and learning new
things.
2. Brain damage is hard to repair because the adult nervous system does not
automatically replace damaged cells and restore lost functions. A number of
surgical techniques have tried to help damaged central nervous systems.
a) Fetal brain tissue grafts have not been successful in humans over the long
term.
b) Transplants of brain tissue from other species have been rejected by
humans.
c) Scientists are currently concentrating on coaxing neural stem cells that
exist in adult brains to form new neurons. Current work tries to solve the
problem that glial cells and proteins block new neurons from making
replacement synaptic connections for those that have been lost or damaged.
(1) When a protein called Nogo is blocked in rats, neurons were able to
make new connections.
(2) Brain grafts can be made more effective by adding naturally
occurring proteins called growth factors, which promote the survival
of neurons.
(3) To promote neural plasticity, special mental and physical exercise
programs seem to help “rewire” damaged brains.
IV. LINKAGES: HUMAN DEVELOPMENT AND THE CHANGING BRAIN
A. PET and fMRI scans, which measure neuronal activity, have shown that brain
functioning changes with age.
1. Newborns’ brain activity is high in the thalamus and low in the part of the
forebrain related to smooth movement. This pattern of brain activity and motor
function resembles that seen after brain damage in Huntington’s disease patients.
2. In the second and third months, brain activity increases in regions of the cortex.
This is paralleled by a loss of reflexes not under cortical control.
3. In the eighth and ninth months, brain activity increases in the frontal cortex,
paralleled with the apparent blossoming of cognitive activity.
4. The brain matures through adolescence, creating more efficient communication
in major fiber tracts.
B. Neural plasticity, not the growth of new cells, is associated with development. In the
first years of life the number of synapses and dendrites increases greatly, then drops in
early adolescence. The brain overproduces neural connections, then “prunes”
unneeded ones.
C. In studies on rats, the richness of the environment—in other words, experience—
determines the number of synapses that are developed and retained throughout life.
V. THE CHEMISTRY OF BEHAVIOR: NEUROTRANSMITTERS
How do biochemicals affect my mood?
Different sets of neurons use different neurotransmitters. About 100 neurotransmitters have
been identified. A group of neurons that communicate using the same neurotransmitter is
called a neurotransmitter system.
A.
Three Classes of Neurotransmitters
1. Small molecules
a) Acetylcholine is used by sets of neurons involved in controlling movement
of the body, in making memories, and in slowing the heartbeat and
activating the digestive system. Alzheimer’s disease may result from
disruptions of this system.
b) Norepinephrine affects arousal, wakefulness, learning, and mood.
Disruptions of this system have been linked to depression.
c) Serotonin affects sleep, mood, aggression, and impulsive behaviors.
Serotonin levels can be affected by what is eaten.
(1) Malfunctions in serotonin systems can result in mood and appetite
problems seen in some types of obesity, premenstrual tension, and
depression.
(2) Antidepressant medications such as Prozac, Zoloft, and Paxil are
thought to act on serotonin systems to relieve some of the symptoms
of depression.
d) Dopamine is used by sets of neurons involved in controlling movement,
and damage to these systems contributes to shakiness experienced by
people with Parkinson’s disease. Other dopamine systems are involved in
the experience of reward, or pleasure, which is vital in shaping and
motivating behavior. Certain other dopamine systems are suspected to be
responsible for the perceptual, emotional, and thought disturbances
associated with schizophrenia.
e) GABA (gamma-amino butyric acid) is the main inhibitory neurotransmitter
in the brain—it slows down the brain’s neural activity.
(1) Some drugs amplify the inhibitory action of GABA. One example is
alcohol, which results in impairments of thinking, judgment, and
motor skills. Drugs that interfere with GABA’s inhibitory effects
produce intense repetitive electrical discharges, known as seizures.
(2) Impaired GABA systems are thought to contribute to severe anxiety,
Huntington’s disease, and epilepsy.
f)
Glutamate is the main excitatory neurotransmitter in the brain. Its release is
associated with the ability of a synapse to “strengthen” its connection
between two neurons, perhaps as part of the physical basis of memory
formation.
(1) Overactivity of glutamate synapses can cause neurons to die by
“exciting them to death.” Blocking glutamate receptors immediately
after brain trauma can prevent permanent brain damage.
(2) Glutamate may contribute to the loss of brain cells in Alzheimer’s
disease.
2. Peptides: Hundreds of chemicals called peptides have been found to act as
neurotransmitters. Examples of these are endorphins, which are used in brain
systems involved in pain perception. Opiate drugs (e.g., morphine) relieve pain
by binding to endorphin receptors.
3. Gases: Two toxic gases that contribute to air pollution have been recently
discovered to act as neurotransmitters: nitric oxide and carbon monoxide. Rather
than bind to receptors, these gases affect the chemical reactions inside nearby
neurons. Nitric oxide is not stored in vesicles and can be released from any part
of the neuron. Nitric oxide appears to be one of the neurotransmitters responsible
for penile erection and the formation of memories.
VI. THE ENDOCRINE SYSTEM: COORDINATING THE INTERNAL WORLD
How can my hormones help me in a crisis?
A. Like the nervous system, the endocrine system is specialized for cell-to-cell
communication. Cells of endocrine glands release chemicals called hormones into the
bloodstream. Then, cells of target organs use specific receptors to detect specific
hormones, causing specific cell responses.
1. The hypothalamus in the brain controls the pituitary gland, which controls
endocrine organs in the body. An endocrine organ’s hormone product affects
cells of a specific target organ of the body.
2. Each part of the system uses hormones to signal the next or to provide feedback
for subsequent hormonal regulation.
a) When threat is perceived, the hypothalamus directs the pituitary to release
the hormone ACTH into the bloodstream.
b) ACTH causes the adrenal gland to release the hormone cortisol.
(1) Adrenal hormones and sympathetic arousal together result in the
fight-or-flight response (e.g., faster heart rate, increased energy use)
to help the body respond to danger.
KEY TERMS
An activity based on the key terms could be used to introduce students to search engines like
PsycINFO or PsycARTICLES. This could be done as an in-class demonstration or as an
assignment.
action potential (pp. 50-52, 55, and 75)
amygdala (pp. 63-64 and 66)
association cortex (pp. 64-65 and 67-69)
autonomic nervous system (pp. 53-54 and 62-63)
axon (pp. 50-57, 61, and 71-72)
biological psychology (pp. 48 and 61)
central nervous system (CNS) (pp. 53-56 and 71-72)
cerebellum (pp. 61-63 and 66)
cerebral cortex (pp. 61, 63-67, and 73)
corpus callosum (pp. 63-64, 66-67, and 69-70)
dendrites (pp. 50-51, 53, and 72-73)
endocrine system (pp. 48 and 76-78)
fiber tracts (p. 55, 61, and 73)
fight-or-flight response (p. 78)
forebrain (pp. 61-64, 66, and 73)
glands (pp. 48, 53-54, and 76-78)
glial cells (pp. 49, 71-72, and 75)
hindbrain (pp. 61-63 and 66)
hippocampus (pp. 63-64 and 66)
hormones (pp. 48 and 76-78)
hypothalamus (pp. 63, 66, and 77)
locus coeruleus (p. 61)
medulla (pp. 61 and 66)
midbrain (pp. 61-63 and 66)
motor cortex (pp. 64-65, 67, 71, and 73)
motor neurons (pp. 54-56)
neural networks (pp. 53 and 66)
nervous system (pp. 48-49)
neural plasticity (pp. 71-72)
neurons (pp. 48-60)
neurotransmitter (pp. 50-53, 72, and 74-77)
nuclei (pp. 54, 61, 63 and 66)
parasympathetic nervous system (pp. 53-54)
peripheral nervous system (pp. 53-54)
reflexes (pp. 55-56)
refractory period (p. 50)
reticular formation (pp. 61 and 66)
sensory cortex (pp. 64-65 and 67)
sensory neurons (pp. 54-56, 65, and 68)
somatic nervous system (pp. 53-54)
spinal cord (pp. 53-56, 61, and 71-72)
sympathetic nervous system (pp. 54 and 77-78)
synapse (pp. 51-53, 56, 71, 73, 75, and 77)
thalamus (pp. 63, 66, and 73)