Transcript The Brain, Biology, and Behavior Neuron

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
Myelin sheath – speeds up transmission
Terminal Buttons – end of axon; secrete
neurotransmitters
 Neurotransmitters – chemical messengers
Synapse – point at which neurons interconnect
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 3.3
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 3.5
A highly magnified view of the synapse. 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.
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
Neural Regulators
 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- Go (fight-or-flight)
 Parasympathetic: Quiets body- Stop
Afferent = toward the CNS
Efferent = away from the CNS
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 X-Ray 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): Computergenerated color image of brain activity, based on
glucose consumption in the brain.
Brain Regions and Functions
Hindbrain – vital functions – medulla,
pons, and cerebellum
 Midbrain – sensory functions –
dopaminergic projections, reticular
activating system
 Forebrain – emotion, complex thought
– thalamus, hypothalamus, limbic
system, cerebrum, cerebral cortex
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Cerebral Cortex
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
 Left hemisphere – verbal processing:
language, speech, reading, writing
 Right hemisphere – nonverbal processing:
spatial, musical, visual recognition
 Corpus Callosum: Bundle of fibers
connecting cerebral hemispheres
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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
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
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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.
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.
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 3.21
Language processing in the brain. This view of the left hemisphere highlights the location of
two centers for language processing in the brain: Broca’s area, which is involved in speech
production, and Wernicke’s area, which is involved in language comprehension.
Language is controlled by the left side of the brain in the majority of rightand left-handers.
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)
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
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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
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.
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
< Low Pituitary
Acromegaly >
< Giantism
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.
Genes and Behavior: The Interdisciplinary
Field of Behavioral Genetics
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Behavioral genetics = the study of the influence of
genetic factors on behavioral traits
 Basic terminology:
 Chromosomes – strands of DNA carrying genetic
information
 Human cells each contain 46 chromosomes in
pairs (sex-cells – 23 single)
 Each chromosome – thousands of genes, also
in pairs
 Dominant, recessive
 Homozygous, heterozygous
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Genotype/Phenotype and Polygenic inheritance
Neurogenesis and Plasticity
Plasticity: Brain’s capacity to change
its structure and functions
 Neurogenesis: Production of new
brain cells
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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.
Modern Approaches to the Nature vs. Nurture Debate
Molecular Genetics = the study of the
biochemical bases of genetic
inheritance
 Genetic mapping – locating specific
genes
 Behavioral Genetics
 The interactionist model
Richard Rose (1995) – “We inherit
dispositions, not destinies.”
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Evolutionary Psychology: Behavior in Terms of Adaptive Significance
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on Darwin’s ideas of
natural selection
Reproductive success key
 Adaptations – behavioral as
well as physical
Fight-or-flight response
Taste preferences