Brain and Behavior

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Chapter 2

• Brain and Behavior

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Neuron and Its Parts

• Neuron Individual nerve cell 100 billion in
  brain
• 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 neurons 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
• 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
• 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
• 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
• 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 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.
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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)
  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
  of the bodys interior
• Functional MRI MRI that makes brain activity
  visible
• Positron Emission Tomography (PET)
  Computer-generated color image of brain activity,
  based on glucose consumption in the brain

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Fig. 2.12 An MRI scan of the brain.
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Fig. 2.13 PET scans.
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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 brains
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 words meaning (Montgomery,
1989).
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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
• Processes information sequentially and is
  involved with analysis
• Right hemisphere good at perceptual skills, and
  at expressing and detecting others emotions
• 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
• 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
• Brocas Area Related to language and speech
  production
• If damaged, person knows what s/he wants to say
  but cant say the words
• Wernickes Area Related to language
  comprehension in left temporal lobe
• 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
• 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
• 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
• RAS acts like the brains 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
• 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
• Hypopituitary Dwarfs As adults, perfectly
  proportioned but tiny
• 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
• Excessive body growth
• Acromegaly Enlargement of arms, hands, feet, and
  facial bones
• Caused by too much growth hormone secreted late
  in growth period
• 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.
• Releases hormone melatonin, which responds to
  daily 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

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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
• Releases epinephrine and norepinephrine (also
  known as adrenaline and noradrenaline)
• 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
• 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)
• 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 Brains 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
patients 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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