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Lecture 13
terms
8
Physiology
Undergraduate 3
03/20/2013

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Term
Action Potential
Definition
Rapid large depolarization is used for communication
Action potentials travel along axons from the cell body to the axon terminal (or if an afferent neuron, from the receptor to the terminal)
Term
Threshold
Definition
Minimum depolarization necessary to induce the regenerative mechanism for the opening of sodium channels
Term
Voltage-gated Na Channel
Definition
•Two gates are associated with the channel
Activation gate and inactivation gate
Term
Activation Gate
Definition
•Voltage dependent
•Opens at threshold and depolarization
•Positive feedback
Term
Inactivation Gate
Definition
Voltage and time dependent
•Opens during depolarization
•Closes during depolarization
Term
All-or-None Principle
Definition
•Threshold
–Minimum depolarization necessary to induce the regenerative mechanism for the opening of sodium channels
•Threshold depolarization  action potential
•Subthreshold depolarization  no action potential
•Suprathreshold depolarization  action potential
•Action potentials from threshold and supra-threshold stimuli are the same magnitude
–100 mV (–70 mV  +30 mV)
Term
Absolute Refractory Period
Definition
–Spans all of depolarization and most of the repolarization phase
–Second action potential cannot be generated
–Na+ gates are inactivated
Term
Relative Refractory Period
Definition
–Spans the last part of the repolarization phase and hyperpolarization
–Second action potential can be generated—with a stronger stimulus
–Some Na+ gates are closed; some are inactivated
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