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What is 1 + 3?
At rest: -70 mV with Na+ outside and K+ inside
A stimulus from a neighboring neuron changes shape of a Na+ channel causing it to open
Na+ ions flood in causing local depolarization: inside positive and outside negative
Enough channels open, enough Na+ comes in to change the onside to about 50mV (threshold potential)
Change in charge opens voltage-regulated, gated channels; more Na+ floods in causing depolarization of 30mV
The change opens K+ gated channels; K+ floods out (Na+ gates close, no more Na+ in) K+ gates close slowly; Repolarization (inside becomes negative again)
Because K+ gates are slow, overshoot to -75mV occurs (hyperpolarization)
Na+/K+ pump puts ions back where they came from and restores resting potential of -70mV
The Na+ that rushed in (step 3) keeps making the next gates open [wave of depolarization (action potential) spreads across the entire neuron membrane and down to axon terminals on to the synapse]