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What are the 6 phases?
- Resting MP
- Depolarization phase
- Repolarization Phase
- Na-K Pump
All voltage-gated ion channels are closed
EPSPs summate, making the interior more positive nad causing the activation gates of voltage-gated Na channels to fly open
- Depolarization phase:
- Na floods into the axon, making the interior more positive (depolarizing the interior) and drives the membrane potential above zero (all the way up to +40)
- Repolarization phase:
- Voltage gated Na+ channels close and voltage-gated K+ channels open. K floods out of hte axon, carrying out positive charge and making the interior negative again, repolarizing it
Voltage-gated K channels are slow to close; and so much K leaves the axon/ cell that the membrane voltage falls below the original resting membrane voltage/ potential
- Sodium-Potassium Pumps
- They are finishing the job. Na-K pumps reaestablish the original ion distribution
- 3 Na+ kicked out; K+ comes in
- Pumping against concentration gradient
no channels open
- Na+ activation gates open, allowing influx of sodium
- Note: Voltage-gated Na+ channnels have 2 gates:
- a) Activation gate opens rapidly at depolarization
- b) Inactivation gate closes slowly at depolarization
- inactivation gates close Na+ channels, and activation gates open K+ channels.
- Note: Voltage-gated K+ channels have one gate
- - This gate opens slowly at depolarization
- Membrane potential temperarily more negative than resting state
- Since K+ gates slow to close
- Refractory period: Neuron insensitive to depolarizing stimuli
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