CHAPTER 3 NEUROSCIENCE AND BEHAVIOR (BIOLOGY AND BEHAVIOR)
Biological psychology: the study of the relationship between biology and behavior and mental
processes
The nervous system is the primary path of communication in your body
neurons: special cells that receive and transmit information from one part of body to
another
In the brain we have approximately
3 types of neurons
1. sensory (afferent) neurons: transmit messages from sense organs to the brain or spinal cord
(including messages from internal organs and skin)
2. motor (efferent) neurons: transmit information from brain or spinal cord to muscles and
glands; help us move our arms, legs, etc.
3. interneurons: transmit messages between neurons
Most neurons are interneurons (in the nervous system)
3 Parts of a Neuron
1. cell body-- sometimes called the soma; contains the nucleus ; gives the neuron energy to
function and can receive information; also contains genetic material
2. dendrites-- short fibers that extend out from the cell body
receive signals from other neurons
some dendrites have more branches than others; this allows the neuron to receive more
information
3. axon-- thin, tube-like structure that extends out from the cell body
Sends information from neuron to other neurons, a gland, or a muscle
Not all neurons have axons, and the ones that do have axons have
only one
Axons can vary in size, can be long or short
The axon ends in the axon terminal, it transmits signals to the dendrites, other cell
bodies, muscles, glands
Neurons are not connected together
Between the axon terminal and the receiving neuron is a tiny gap called the
synaptic cleft
synapse-- the point of communication between the axon terminal of a neuron
and a receiving neuron
Sending neuron—presynaptic neuron
Receiving neuron—postsynaptic neuron
How the Neuron Communicates
On the outside-- sodium ions which are positively charged
On the inside-- potassium ions which are negatively charged
When the neuron is at rest, it has more negative ions inside,
More positive ions outside,
When at rest, the neuron is at
millivolts of electricity
This is called the resting potential
When the neuron is stimulated, the electrical impulse does not travel down the neuron
When the neuron is disturbed just a little, it’s no longer resting and it reaches threshold (a minimal
disturbance)
It gets to be fully stimulated and the sodium channels open and sodium rushes into the cell, then
the channels close, this makes the cell more positive inside
Very soon after the sodium channels close, the potassium channels open and potassium rushes
out of the cell, then those channels close, making the cell more negative outside
The neuron becomes more positively charged at
events is called the action potential
millivolts and this series of
The action potential is based on the “all-or-none” law, meaning that the neuron fires completely
or not at all
How does it get back to its resting potential?
Sodium ions begin to flow out of the neuron and potassium ions begin to flow back in
So the neuron is back at -70 millivolts
a neuron can fire up to
action potentials a second
the impulse will travel faster if the axon is covered with myelin sheath, a white, fatty coating that
acts as insulation for the axon by protecting it from other axons
The impulse on an axon with the myelin sheath can travel
myelin sheath
faster than without the
nodes of Ranvier: gaps between the segments of the myelin sheath where the electrical
impulse is regenerated at each node
If there is damage done to myelin along the axon, messages that are transmitted can be slowed or
interrupted
The result is
You will see this in multiple sclerosis, which has degeneration of parts of the
myelin sheath
glial cells: are even smaller than neurons and they outnumber neurons by 10:1
Other functions of glial cells 1)
2)
3)
4)
Neurotransmitters
Messages between neurons are transmitted by chemical messengers called neurotransmitters:
little chemical messengers
Neurotransmitters are held in the synaptic vesicles , little sacs in the axon terminal
When an action potential reaches the axon terminal, the synaptic vesicles release their
neurotransmitters inside it and the neurotransmitters move into the synaptic cleft
Neurotransmitters have a distinctive shape; the receptor site of the receiving cell is coordinated
with the shape of the neurotransmitter
Acetylcholine: first neurotransmitter to be discovered; is found in all motor neurons
This is the neurotransmitter that helps you to move, stimulates muscle contractions,
stimulates muscle movements as small as blinking your eyes or as big as jumping a hurdle
Is also important for
Loss of memory in
is associated with a
loss of acetylcholine
Dopamine: Involved in movement
People with
have a depletion of dopamine in
their brains; move rigidly, have tremors; movements aren’t synchronized or don’t flow smoothly;
sometimes it’s just hard for them to get moving; also affects speech
Also involved in the reward center of our brains
Ex:
Serotonin:Is involved in your emotional states and sleep
Lower levels of serotonin can lead to depression
Need serotonin to sleep
The higher the level of serotonin, the sleepier you will be
THE CENTRAL NERVOUS SYSTEM
The central nervous system can be seen as the central processing center of your body;
everything that you do, sense, feel, or think has to be processed through your central nervous
system
Our nervous system has two parts:
The spinal cord is about the size of your little finger in diameter and has tons of glial cells
The spinal cord does not have to act with the brain, it can act alone
For instance, the spinal cord can act without the brain to protect us from
being injured
Ex:
THE BRAIN
About how much does your brain weigh?
Brainstem
That part of the brain right at the top of the spinal cord and at the base of the brain
Many of our
are controlled by parts
of the brainstem
medulla: controls breathing, heart rate, digestion, blood pressure, coughing, and
swallowing
Any damage is usually fatal
Ex:
reticular formation: regulates sleep and attention
If it’s very active, we are alert
If it’s slow, we go to sleep
pons: it connects the right and left cerebellum
Helps coordinate body movements for each side of the body
cerebellum: controls basic muscle coordination and movements;
movements are more fluid-like, more smooth
Also controls
Ex:
Damage to the cerebellum:
Ex:
The Limbic System
thalamus: processes sensory and motor information and sends the
information to higher brain areas
Most information that comes in (except for
the thalamus before it goes to other parts of the brain
) has to stop by
Also involved in
hypothalamus: a small, peanut-sized structure located under the thalamus
Regulates those behaviors that we need to survive, like eating,
drinking, sexual and emotional behavior
Also regulates
amygdala: important for expressing emotions
Involved in emotions like fear and anger
If it’s stimulated, person can show fear in a situation
hippocampus: important in forming new memories
If damaged or destroyed, you will not be able to store or
recall any new information
You can remember old information because old
memories are not stored in the hippocampus
It affects only those memories after the damage
Ex:
THE CEREBRAL HEMISPHERES
The cerebral cortex is the outer covering of the brain and is made up of two halves called the
cerebral hemispheres
The cerebral cortex is only about 1/8” thick and is very wrinkled and gray; where the term
“gray matter” comes from
Controls memory, thinking, and language
Hemispheres are connected by the corpus callosum, a thick band of axons that allows the right
and left hemispheres to communicate with each other
Each hemisphere controls the opposite side of the body
Right hemisphere controls feeling and movement for the left side of the body
Left hemisphere controls feeling and movement for the right side of the body
Lobes of the Brain
1) frontal lobe: the largest lobe, the front part of the brain
Involved in planning, thinking, executing voluntary movements, creativity, and emotions
2) parietal lobe: involved in processing sensory information, including touch, temperature, and
pressure; in the middle
Helps us identify things by touch, such as a pencil
3) occipital lobe: receives and interprets visual information; located at the back of the brain
4) temporal lobe: receives and interprets auditory information; located by your temples
BRAIN DAMAGE
Damage to certain parts of the brain can result in severe impairment or death
stroke: most common cause of injury to the adult brain and is the 3 rd most
common cause of death
Occurs when blood supply is cut off to part of the brain, brain
doesn’t get enough oxygen and brain cells are killed
Can be caused by a blood clot, hemorrhaging in the brain, etc.
Can lead to
head injury result in impaired motor coordination
Can lead to
Recovering from brain damage
Once you lose neurons, they are gone forever and cannot be replaced
If have damaged neurons, they can sprout new dendrites and make new
connections with other neurons
If lose some abilities because of damage, other areas can take over the
functioning if they are near the site; you can regain those abilities
Plasticity-- where the brain reorganizes and compensates for damage done
show greater levels of plasticity because all the
connections have not been made yet
THE PERIPHERAL NERVOUS SYSTEM
Contains all the nerves that are on the outside of the central nervous system; connects the central
nervous system to the rest of your body
Divided into 2 subdivisions:
1) Somatic Nervous System
Transmits information from sensory receptors to central nervous system
AndTransmits messages from central nervous system to motor nerves to muscles
Controls voluntary movements
2) Autonomic Nervous System
Controls involuntary functions
Transmits information between central nervous system and the heart, smooth muscles, and glands
Involuntary functions include
The autonomic nervous system is broken down into two subsystems:
1) sympathetic nervous system: turned on when you need to use energy
Usually turned on in emergencies; also includes heightened emotions
Symptoms:
Is called the fight-or-flight response, how your body prepares you to
fight or run from something that’s dangerous
2) parasympathetic nervous system: tries to conserve energy and is turned on after an
emergency to calm you down
THE ENDOCRINE SYSTEM
Made up of glands throughout the body and they communicate with other parts of the body by
manufacturing and secreting hormones
Hormone: chemical messengers that are released into the bloodstream to other
parts of the body
It affects whatever part of the body it is released to
pituitary gland-- called the master gland; about the size of a pea and
located right under the brain
Controlled by the hypothalamus
Controls the hormones produced by other glands in the
endocrine system
Produces the hormone that
thyroid: controls your body’s metabolism, produces a hormone called thyroxin
adrenal glands: produces norepinephrine and epinephrine (also called adrenaline)
These hormones turn on your sympathetic nervous system
They are hormones and
pancreas: regulates your blood sugar levels by releasing insulin into your
bloodstream
gonads: sex glands
in females called the
In males called the
Needed for reproduction
Responsible for secondary sex characteristics during puberty
(girls develop breasts, boys voices get deeper, etc.)
The male sex hormones are androgen and testosterone, which influences sex
drive
The female sex hormones are estrogen and progesterone and they help to
regulate the menstrual cycle
Both males and females are born with these hormones, just in different proportions