Resting membrane potential: channels are closed (inactivation na gates are open, no ion-gated channels open only leak channels stimulus)

2) depolarization: na+ activation gates open, threshold is reached -55mv, sodium flows in, positive feedback loop (more depolarization, more gates opening, more na+ flowing in all the way to about +35mv)

3) repolarization: peak happens because the na+ inactivation gates are fully closed, k+ channels then open

4) hyperpolarization: na+ activation gates close below threshold, k+ gates are still open, too much k+ flows out of cell because the gate is slow, making rmp too low
-- k+ ion absorbed by astrocytes on outside to reset the charges to about -70mv as well as the sodium potassium pump bringing back the maintaining chemical gradient by throwing out na+ and bringing k+ back in