what occurs during the falling phase?
the behavior of two types of channel contributes to the falling phase. First,m the voltage gated sodium channels inactivate. Second, the voltage-gated potassium channels finally open (triggered to do so 1 msec earlier by the depolarization of the membrane). There is a great driving force on K ions when the membrane is strongly depolarized. Therefore, K ions rush out of the cell through the open channels, causing the membrane potential to become negative again.