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information
m） The Visual Cortex； located in the occipital lobes； processes visual
information
n） The Association Cortex； which includes all of the cortex that is unlabeled；
works to interpret and integrate information from many parts of the brain
5。 Hemispheric Lateralization
a） Roger Sperry and Michael Gazzaniga devised situations that could allow
visual information to be presented separately to each hemisphere。
b） Information from the right visual field goes to the left hemisphere； and
information from the left visual field goes to the right hemisphere
c） Speech may be the most highly lateralized of all brain functions。 For most
people； speech is a left hemisphere function。
d） The left hemisphere tends to be more analytical； processing information bit
by bit
e） The right hemisphere tends to be more holistic； processing information in
global patterns
f） There may be gender differences in lateralization。 When making
judgments； the left hemispheres of males showed more activity； while both
hemispheres of females showed activity
E。 The Endocrine System
1。 A highly plex munication system prised of a network of glands that
supplements the work of the nervous system
a） Hormones–“the messengers of life”–are chemicals secreted by the glands of
the endocrine system。 They influence sexual development； physical
growth； moods； arousal level； immune functioning； and metabolism rate。
2。 The Hypothalamus serves as an intermediary between the endocrine system and the
nervous system。 Messages from the brain cause the hypothalamus to release
hormones to the pituitary gland。
3。 The Pituitary Gland； the “master gland；” secretes about ten different types of
hormones； which influence the functioning of all other endocrine system glands； and
influences growth
a） In males； the pituitary gland activates secretion of testosterone； which leads
to sperm production
b） In females； the pituitary gland activates secretion of estrogen； which is
essential to the release of eggs from the ovaries
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CHAPTER3： THE BIOLOGICAL BASES OF BEHAVIOR
III。 The Nervous System in Action
A。 The Neuron
1。 The neuron is a cell specialized to receive； process； and transmit information to other
cells。 There are at least 200 different types of neurons； which are typically prised
of dendrites； soma； axon； and terminal buttons。
a） Dendrites are branched fibers that extend outward from the body of the
neuron and that receive messages from other neurons
b） The Soma； or cell body； integrates information received by the dendrites
and passes it along to the axon
c） The Axon is a single extended fiber that conducts information to terminal
buttons
d） Terminal buttons are bulblike structures that secrete neurotransmitters
which influence other neurons
2。 There are three major classes of neurons： sensory neurons； motor neurons； and
interneurons
a） Sensory neurons carry messages from sense receptors toward the CNS
b） Motor neurons carry messages from the CNS to the muscles and glands
c） Interneurons carry messages between different neurons
3。 Glia cells； derived from the Greek word for “glue；” outnumber neurons in the brain by
about five or ten to one and perform three primary functions： housekeeping；
insulation； and protection of the brain
a） Development： Glia cells help guide newborn neurons to appropriate
locations in the brain
b） Housekeeping： Glia cells clean up after neurons die and absorb excess
neurotransmitters
c） Insulation： Glia cells form a myelin sheath around the axon of some types
of neurons； greatly increasing the conduction speed of the axon
d） Protection： Glia cells form a blood…brain barrier that prevents toxins from
reaching the brain
B。 Action Potentials
1。 Neurons send messages in an all…or…none fashion through action potentials traveling
down the axon； and they receive messages in the form of graded potentials through
the dendrites
a） Excitatory input increases the likelihood that a neuron will fire
b） Inhibitory input decreases the likelihood that a neuron will fire
c） Graded Potentials are generated by excitatory inputs and vary in size
according to the magnitude of the stimulation。 One graded potential is
often not enough to cause a neuron to fire
39
PSYCHOLOGY AND LIFE
d） Temporal Summation involves several excitatory or inhibitory inputs from
the same source over time
e） Spatial Summation involves several excitatory or inhibitory inputs from
different sources at the same time
2。 The Biochemical Basis of Action Potentials
a） An Action Potential begins when excitatory inputs are strong enough to
overe inhibitory inputs and involves depolarization of the neuron by
sodium ions rushing into the cell
b） Resting Potential is the slightly negative voltage of a neuron in a resting
state
c） Ion Channels in neuron membranes respond to changes in excitatory and
inhibitory input。 Excitatory input causes the ion channels to allow sodium
ions into the neuron； allowing the neuron to fire。 Inhibitory input causes
the ion channels to keep the neuron negatively charged； preventing the
neuron from firing。
d） The action potential then travels down the axon as adjacent areas of the
axon successively depolarize
e） When the fluid inside the neuron bees positive； the sodium ion
channels close and potassium ion channels open； allowing potassium
ions to exit the cell； restoring negative charge of the neuron。
f） Action potentials obey the All…or…None Law。 The size of the action potential
is not influenced by the intensity of stimulation beyond the threshold level。
g） After firing； neurons enter a Refractory Period； a period during which they
cannot fire or will only fire with more intense stimulation dm normal
C。 Synaptic Transmission
1。 Transmission of neural impulses between neurons involves the movement of
neurotransmitters across the synaptic cleft
a） A Synapse is a small physical gap between neurons
b） Once an action potential reaches an axon terminal button； vesicles release
neurotransmitters into the synaptic gap chemical substances that
stimulate other neurons。 The neurotransmitters then traverse across the
synaptic gap and attach to receptor molecules embedded in the
postsynaptic neuron membrane。
D。 Neurotransmitters and Their Functions
1。 At least 60 substances are suspected to function as neurotransmitters in the brain
2。 Acetylcholine； a neurotransmitter found in both the central and peripheral nervous
systems； is implicated in memory loss associated with Alzheimer’s disease and in
some types of respiratory failure
3。 Gamma…Amino Butyric Acid （GABA） is thought to be related to anxiety； as depressants
bind to receptor molecules sensitive to GABA and cause sedation
4。 Catecholamines such as dopamine and norepinephrine play prominent roles in mood
disturbances and schizophrenia
40
CHAPTER3： THE BIOLOGICAL BASES OF BEHAVIOR
a） Decreased levels of norepinephrine have been related to depression
b） Increased levels of dopamine have been related to