chapter 3: biological bases of behavior. communication in the nervous system
TRANSCRIPT
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CHAPTER 3: BIOLOGICAL BASES OF BEHAVIOR
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COMMUNICATION IN THE NERVOUS SYSTEM
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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
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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
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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)
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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
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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)
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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
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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
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NEUROTRANSMITTERS
Most stored in synaptic vesicles in the terminal buttons
They diffuse into the synaptic cleft
Picked up by receptor sites of receiving neuron
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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
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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
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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)
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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
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ACETYLCHOLINE (ACH)
Only transmitter btwn motor neurons and voluntary muscles
Also contributes to attention, arousal, and possibly memory
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AGONIST AND ANTAGONIST
Agonist: chemical that mimics the action of a neurotransmitter
Antagonist: chemical that opposes the action of a neurotransmitter---they block receptors
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MONOAMINES
Include dopamine, norepinephrine, and serotonin
Dopamine: voluntary movement, pleasurable emotions
Serotonin: sleep and wakefulness; aggression and impulsivity
Norepinephrine: modulation of mood, arousal
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ABNORMALITIES WITH MONOAMINES
Low levels of norepinephrine and serotonin synapses tied to depression
Abnormal dopamine activity tied to schizophrenia
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ENDORPHINS
Def: the family of internally produced chemicals that resemble opiates in structure and effect
Discovered by study of morphine effects
Regulate pain, pleasure