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 (AC H ) 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