A quick look at the action potential action potential is a rapid reversal of the resting membrane resting ( 70mv) to depolarization (+35mv) then repolarization ( 70mv) Membrane potential then briefly becomes more negative, hyperpolarization ( 90mv) then back to resting ( 70mv) rapid changes in membrane potential caused by the movement of ions across the membrane: sodium ions (na+, potassium ions (k+) When the inactivation gate is closed, the channel will not open, regardless of the strength of stimulation, called the absolute refractory period. Na+ voltage-gated channels open first and then become inactivated, producing the. K+ voltage-gated channels then begin opening as the na+ channels begin entering the absolute refractory period inactivated period. 70 mv: k+ continues to rush out of the cell and the membrane hyperpolarizes (reaches . 90 mv: k+ channels begin to close and k+ no longer leaves the cell, membrane potential slowly returns to resting value of 70 mv.