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