Action Potential Flashcards
Axon Hillock
where the Axon joins the Soma
Action Potential
Depolarization of Neuron
Cell “Fires” AKA “Spikes”
= changes in membrane permeability of Axon, propagated via IONIC CONDUCTION
- triggered by NT from other Neuron, electrical stimulation, or other
Voltage activited Na+ gates
open first when the threshold potential is met
Na+ rushes in, reverse LOCAL polarization (depolarizes to +50mV)
Na+ moving inside causes..
…adjacent Na+ voltage activated gates to open and previously open ones close
- this depolarization sequence continues along Axon toward Terminal
As previous Na+ gates close, local K+ gates…
…open wide, K+ leaves (now per both chem and electrical gradients)
Na+ gates continue to close, and K+ to open, following behind depolarization that is moving along Axon
When depolarization reaches TERMINAL
Ca++ gates there open and Ca++enters the cell
Ca++ influx leads to Neurotransmitter release
As Membrane Potential again approaches more positive outside than inside from K+ outflow,
K+ gates begin to close
in time, Sodium potassium pump actively restores Resting Potential
Refractory Period
while the cell is being re-polarized, it cannot fire (or resists firing)
prevents impulse from being propagated back along Axon toward Soma (since previously opened Na+ gates locked)
Absolute Refractory Period
Na+ gates will not open, no Action Potential possible
Relative Refractory Period
Na+ gates can open
but K+ gates still wide open, so stronger stimulus required
All or None Law
in a given cell, an AP always has the same amplitude and velocity, regardless of the intensity of the stimulus that triggered it
While the amplitude of the Spike and amount of NT released is FIXED, the “message” such a cell can transmit can be varied through its…
…frequency of firing and Pattern of Firing
Frequency of Firing
number of spikes per second
Pattern of Firing
vs.
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