Chapter 2
Brain and Behavior
Weekly Reading Guarantee
1. What is the action potential? In other words, do neurons fire half
way? As in communicate half a signal? Or is it an all or nothing
event?
2. Is there more than one nervous system? Are we conscious of
everything our nervous system is doing?
Grounding this information in
something coherent
Phineas Gage
http://www.youtube.com/watch?v=kc213m
MSsjY
Neuron’s Parts
– Soma: Cell body; body of the neuron.
Receives messages and sends messages
down axon
– Axon: Fiber that carries information away
from the cell body of a neuron
– Axon terminals: Branches that link the
dendrites and somas of other neurons
– Dendrites: Receive messages from other
neurons
A neuron, or nerve
cell. In the right
foreground you
can see a nerve
cell fiber in cross
section. The upper
left photo gives a
more realistic
picture of the
shape of neurons.
Nerve impulses
usually travel from
the dendrites and
soma to the
branching ends of
the axon. The
nerve cell shown
here is a motor
neuron. The axons
of motor neurons
stretch from the
brain and spinal
cord to muscles or
glands of the body.
Fig. 2-1, p. 49
The interior of an axon.
The right end of the top
axon is at rest. Thus, it has
a negative charge inside.
An action potential begins
when ion channels open
and sodium ions (Na+) rush
into the axon. In this
drawing, the action
potential would travel from
left to right along the axon.
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 that it can fire
again. Sodium ions that
enter the axon during an
action potential are
pumped out more slowly.
Removing them restores
the original resting
potential.
Fig. 2-4, p. 51
The Nerve Impulse
• Resting potential: Electrical charge of an
inactive neuron
• Threshold: Trigger point for a neuron’s firing
• Action Potential: Nerve impulse: This is an all
or nothing event, they cannot fire half-way
Electrical probes placed inside and outside an axon measure its activity. (The scale
is exaggerated here. Such measurements require ultra-small electrodes, as
described in this chapter.) The inside of an axon at rest is about –60 to –70
millivolts, compared with the outside. Electrochemical changes in a neuron
generate an action potential. When sodium ions (Na+) that have a positive charge
rush into the cell, its interior briefly becomes positive. This is the action potential.
After the action potential, positive potassium ions (K+) flow out of the axon and
restore its negative charge.
Fig. 2-2, p. 50
More on Nerves
• Ion channels: Tiny openings through the axon
membrane
• Negative after-potential: A drop in electrical
charge below the resting potential
• Synapse: Microscopic space between two
neurons over which messages pass
A highly magnified view of a synapse.
Neurotransmitters are stored in tiny sacs
called synaptic vesicles (VES-ih-kels).
When a nerve impulse reaches the end of
an axon, the vesicles move to the surface
and release neurotransmitters. These
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. Some transmitter
molecules excite the next neuron and
some inhibit its activity.
Fig. 2-5, p. 51
Neurotransmitters
• Chemicals that alter activity in neurons; brain
chemicals
• Receptor site: Area on the surface of
neurons and other cells that is sensitive to
neurotransmitters or hormones
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
• Types of Neurotransmitters
– Acetylcholine: Activates muscles
– Dopamine: Muscle control
– Serotonin: Mood and appetite control
Neuroplasticity
• Capacity of our brains to change in response
to experience
• This idea is present in musicians having more
developed music areas of the brain
• And brain injury clients recovering and
developing language in areas of the brain not
usually associated with language
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
How are the Mind and Brain Related?
• You are looking at a PET scan of your brain while the radiologist taking the
scan is sitting with you. You are discussing the activity depicted on the
screen. As you are staring at the PET scan, the radiologist points out that
the most active areas seen on the screen are in the left hemisphere,
particularly the language area and the visual areas toward the back of the
brain. At this moment you hear some music, and almost immediately the
activity pattern of the scan changes. Now there is activity in the right
hemisphere as well, and you call the radiologist’s attention to that change.
“That’s somewhere in the region of the music appreciation center,” she
responds. Then a few minutes later she asks, “Do you have any comments
on the PET scan?” “What do you mean?” you reply, and, at this point, you
notice another change. The auditory areas, as well as the frontal lobes
(responsible for rewards, cognition, attention, understanding), light up.
You look toward the radiologist and see that she is smiling, and you finally
realize that the PET scan is depicting your own brain activity! It is showing
a shift as you change from one thinking activity to another.
• Is this an example of your mind studying your brain, or is it the brain
studying itself?
Two Divisions of the Peripheral Nervous
System
• 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 digestion pressure
Two Divisions of the Autonomic Nervous
System
• Sympathetic: Arouses body; emergency
system
• Parasympathetic: Quiets body; most active
after an emotional event
Syllabus Update!
• I forgot to mention, there is a public speaking
component to this class. I will call on 5 students
randomly each class session to present what they
learned from the previous reading. You have 5
minutes to prepare your speech. Everyone needs to
be ready in case I call on you
• What happened when I said that? How did your
sympathetic (prepares for emergencies) nervous
system respond?
• We will do deep breathing to help your
parasympathetic nervous system calm you down
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
The Spinal Cord and Behavior
• Reflex Arc: Simplest behavior; 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
A sensory-motor arc, or 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. Such reflexes
provide an “automatic” protective device for
the body.
Fig. 2-9, p. 54
Brain Imaging Techniques
• 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 body’s interior
• Based on the Localization of Function
• Research strategy of linking specific
structures in the brain with specific
psychological or behavioral functions
Identifying Parts of the Brain
• Imagine the people around you (your group)
are a team of neuroscientists. You believe that
you have identified a region of the brain
responsible for “being a jerk”. What
techniques could you use to verify you found
the right structure of the brain?
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
More Brain Imaging Techniques
• 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
• Electroencephalograph (EEG)
• A device that detects, amplifies, and records
electrical activity in the brain
Fig. 2-12, p. 58
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.
Fig. 2-11, p. 57
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.
Fig. 2-14, p. 59
Participants were
asked to tell the
truth or to lie while
fMRI images of
their brains were
taken. When
compared with
telling the truth
(shown in blue),
areas toward the
front of the brain
were active during
lying (shown in
red).
Fig. 2-15, p. 59
Cerebral Cortex
• Definition: Outer layer of the brain; 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 cortex
What role could culture play in this?
•
Different religions, countries and cultures have diverse attitudes concerning the
rights of humans to intervene medically to save a life and also concerning the
disposition of a person’s body after death. Compare and contrast the following
views:
•
•
•
•
a. Blood transfusions should not take place.
b. The body should not be violated after death.
c. Parts of the dead should be immediately used for transplants.
d. A person’s body should be cremated at death.
•
Also, give your opinions as to ways that different cultures might make greater or
lesser use of the various strengths of the right and left cerebral hemispheres.
Corpus Callosum
• Bundle of fibers connecting cerebral
hemispheres
• Allows both sides of the brain to communicate
• Maybe be cut, in the case of someone with
severe epilepsy to prevent seizures from
spreading
• Results in a “split brain” subject
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
Neurological Soft Signs
• Subtle behavioral signs of brain dysfunction
– Clumsiness
– Awkward gait
– Poor hand-eye coordination
– Other perceptual and motor problems
Fig. 2-17, p. 60
A circle is flashed to the left brain of a split-brain patient and he is asked what he saw.
He easily replies, “A circle.” He can also pick out the circle by merely touching shapes
with his right hand, out of sight behind a screen. However, his left hand can’t identify
the circle. If a triangle is flashed to the patient’s right brain, he can’t say what he saw
(speech is controlled by the left hemisphere). He also can’t identify the triangle by
touch with the right hand. Now, however, the left hand has no difficulty picking out the
triangle. In other tests, the hemispheres reveal distinct skills, as listed above the
drawing.
Fig. 2-20, p. 62
Hemispheres
• Left hemisphere better at math, judging time and
rhythm, and coordinating order of complex
movements
– Processes information sequentially
• Right hemisphere good at perceptual skills, and at
expressing and detecting other’s emotions
– Good at recognizing patterns, faces, and melodies
– Processes information simultaneously and
holistically
• Humans use 95 percent of our left brain for language
– Speaking, writing, understanding
Cortical Localization and Interference
• Simultaneously move the right hand and right foot in
a clockwise direction for a few seconds.
• Next, make the right hand and left foot be moved in
a clockwise direction.
• Make circular movements in opposite directions with
the right hand and the left foot.
• Move the right hand and right foot in opposite
directions.
• Was one of these more difficult than the others?
Why do you think that is? Think in terms of probable
activity in the motor areas of the cortex.
Frontal Lobe
• Movement, sense of smell, higher mental
functions
– Contains primary motor cortex; controls motor
movement
• Mirror neurons: Contained in motor cortex;
become active when motor action is carried out
and when another organism is observed
carrying out the same action
The intense social isolation of
autism spectrum disorder may arise
because of damage to mirror
neurons distributed throughout the
brain. (potential cause)
p. 65
Broca’s Area
• Related to grammar and pronunciation
– 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
– If damaged, person has problems with
meanings of words, NOT pronunciation
Fig. 2-22, p. 63
Fig. 2-23, p. 64
Specialized Brains
What are the advantages and
disadvantages of having such
specialized brain functions and
areas? In terms of plasticity, brain
damage & cognitive efficiency
Spatial neglect.
A patient with
right-hemisphere
damage was
asked to copy
three model
drawings. Notice
the obvious
neglect of the
left side in his
drawings.
Similar
instances of
neglect occur in
many patients
with righthemisphere
damage
Fig. 2-18, p. 61
Pituitary Problems
• Too little growth hormone means person will
be smaller than average
– Hypopituitary dwarfism: As adults, perfectly
proportioned but tiny
• Treatable by using human or synthetic
growth hormone; will add a few inches
• Regulates growth via growth hormone
• Its hormones influence other endocrine
glands
Pituitary Problems (cont)
• Too much growth hormone leads to gigantism
(excessive body growth)
• Acromegaly: Enlargement of arms, hands,
feet, and facial bones; due to too much
growth hormone secreted late in growth
period
– Andre the Giant
• Pituitary also governs functioning of other
glands, especially thyroid, adrenals, and
gonads
The Pineal Gland
• Regulates body rhythms and sleep cycles
– Releases the hormone melatonin, which
responds to daily variations in light
The Thyroid Gland
• 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, and depressed
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
Adrenal Malfunctions
• Oversecretion of adrenal sex hormones can
cause virilism: exaggerated male
characteristics (bearded woman)
– May also cause premature puberty if
oversecretion occurs early in life
Fig. 2-27, p. 70
Handedness
• Preference for right or left hand in most activities
• Dominant Hemisphere: Term usually applied to
the side of the human brain that produces
language
• Lateralization: Specialization in abilities of brain
hemispheres
Research suggests that the hand position
used in writing may indicate which brain
hemisphere is used for language
Fig. 2-29, p. 74
Brain Dominance
The functioning of the left and right hemispheres of the brain that may
show dominance of one hemisphere over the other can be
demonstrated by observing lateral eye movement. Spontaneous
lateral eye movement reflects activity in one or other of the
hemispheres of the brain. Eye movement to the left seems to indicate
involvement of the right hemisphere, and movement to the right
appears to involve the left side. It has been observed that some
people shift their eyes to the left more often than to the right. These
are called left-movers. Others typically shift to the right and are called
right-movers.
A conclusion drawn by researchers in this area is that left-movers
have right hemisphere dominance and tend to be more artistic,
creative, and intuitive thinkers. Right movers have left hemisphere
dominance and tend to be more logical, analytical, verbal, and
numerical. These conclusions are considered to be general
tendencies and therefore should be viewed with a skeptical eye. More
study and research is needed to support these conclusions.
1. Five students are to be the subjects of the
demonstration. They will leave the room while
preparations are made.
2. I will ask the subjects a list of questions. The students
are to observe and record the eye movements of each
subject when the questions are asked. Caution them that
the eye movements may be slight and will be to the left or
right. They will have to observe with care (and they will not
have the benefit of slow motion or instant replays).
3. Provide each student with a copy of the record sheet,
which contains the questions and a space to record the
subjects’ responses.
4. Admit the subjects, one at a time, and have each one
stand in front of the class in full
view of the students.
5. I will ask each question and give the subject time to
respond. The students will record their observation for
each question. I will accept whatever answer is given and
move on.
6. After all subjects have been questioned, tally the
number of observed left and right eye movements for each
question and each subject.
An analysis of the results should attempt to see:
which items tended to elicit a left eye shift,
indicating right hemisphere activity and which
elicited a shift to the right, pointing to a left
hemisphere involvement.
if any subject had a tendency to shift more in one
direction than the other, indicating a left or right
hemisphere dominance.
The record sheet provided has a series of
questions which follow a pattern. All oddnumbered items should elicit left
hemisphere activity (eye shift to the right), and
even-numbered items should elicit right
hemisphere activity (eye shift to the left).
Then they should ask the subjects about their preferences for
left or right hemisphere activities to see if the eye movements
do relate to hemisphere dominance.
Finally, critique the exercise as a scientific endeavor. Was it
scientific? Are the results valid? Reliable? Useful?
A conclusion drawn by researchers in this area is that leftmovers have right hemisphere dominance and tend to be
more artistic, creative, and intuitive thinkers. Right movers
have left hemisphere dominance and tend to be more
logical, analytical, verbal, and numerical.