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 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