During what part of the action potential do voltage-gated na+ channels begin to inactivate (their inactivation gates close)? view available hint(s) during what part of the action potential do voltage-gated na+ channels begin to inactivate (their inactivation gates close)? at the beginning of an action potential, as the membrane potential reaches threshold at the end of the depolarization phase, as the membrane potential approaches its peak value at the end of the hyperpolarization phase of an action potential, as the membrane potential returns to its resting value at the end of the repolarization phase, as the membrane potential briefly passes its resting value