CHAPTER 3: BIOLOGICAL
BASES OF BEHAVIOR
COMMUNICATION IN THE
NERVOUS SYSTEM
NERVOUS TISSUE: THE BASIC
HARDWARE
2 major categories of cell in the nervous system:
1: Glia---”glue”; provide structural support and
insulation for neurons
2: Neuron---individual cell in the nervous system
that receive, integrate, and transmit information

NEURON STRUCTURE
Soma: cell body; contains nucleus
 Dendrite: receive info.
 Axon: long, thin fiber; transmits signals from
soma to other neurons or muscles/glands
 Myelin sheath: insulating material (glia) around
axon
 Terminal button: secrete neurotransmitters
 Synapse: space btwn neurons; info transmitted

NEURAL IMPULSE: AT REST




Complex electrochemical reaction
+ charged Na and K ions and neg. charged chloride ions
flow across membrane
Higher concentration of neg ions inside cell; creates voltage
Resting potential: a neuron’s stable, negative charge when
the cell is inactive (c. -70 millivolts)
NEURAL IMPULSE: ACTION
POTENTIAL
When neuron is stimulated
 Ion channels open; + charged Na ions rush in
 Charge is less neg. or even pos.
 This creates an Action potential: brief shift in a
neuron’s electrical charge that travels along an
axon

NEURAL IMPULSE: REFRACTORY
Na channels close
 Absolute refractory period: min. length of time
after an action potential during which another
AP cannot begin (1 or 2 milliseconds)

ALL-OR-NONE LAW
Neuron either fires or doesn’t
 Action potentials are all the same size
 Rate of action potentials tells strength of stimuli
 Size of axon effects rate

SYNAPSES
Neurons do not touch
 Synaptic cleft: microscopic gap btwn terminal
button of one neuron and the cell membrane of
another
 Msgs. in the form of neurotransmitters: chemical
info. from one neuron to another

NEUROTRANSMITTERS
Most stored in synaptic vesicles in the terminal
buttons
 They diffuse into the synaptic cleft
 Picked up by receptor sites of receiving neuron

POSTSYNAPTIC POTENTIALS (PSP)
Def: a voltage change at a receptor site on a
postsynaptic cell membrane
 Vary in size
 Increase or decrease probability of an impulse

TYPES OF MESSAGES
Excitatory PSP: a positive voltage shift; increases
likelihood that a postsynaptic neuron will fire
action potentials
 Inhibitory PSP: neg. voltage shift; decreases
likelihood that a postsynaptic neuron will fire
action potentials

REUPTAKE
Def: a process in which neurotransmitters are
sponged up from the synaptic cleft by the
presynaptic neuron
 Recycles material
 Some NT’s are inactivated by enzymes or
removed (drift away)

NEUROTRANSMITTERS AND
BEHAVIOR
Over 100 possible NTs have been identified
 Specific NTs only work in specific receptors
 This is called the lock-and-key principle
 Meant to prevent mixing of NTs

ACETYLCHOLINE (ACH)
Only transmitter btwn motor neurons and
voluntary muscles
 Also contributes to attention, arousal, and
possibly memory

AGONIST AND ANTAGONIST
Agonist: chemical that mimics the action of a
neurotransmitter
 Antagonist: chemical that opposes the action of a
neurotransmitter---they block receptors

MONOAMINES
Include dopamine, norepinephrine, and serotonin
 Dopamine: voluntary movement, pleasurable
emotions
 Serotonin: sleep and wakefulness; aggression and
impulsivity
 Norepinephrine: modulation of mood, arousal

ABNORMALITIES WITH
MONOAMINES
Low levels of norepinephrine and serotonin
synapses tied to depression
 Abnormal dopamine activity tied to
schizophrenia

ENDORPHINS
Def: the family of internally produced chemicals
that resemble opiates in structure and effect
 Discovered by study of morphine effects
 Regulate pain, pleasure
