Order the steps and events in the action potential. Match the step number to its event(s): Input stimulus causes membrane potential to rise to a threshold levell Na + channel opens and Na + diffuses into the cell. Change in membrane potential caused by Na + entering the cell opens K + channels Overshoot closes the Na + channels. Membrane potential becomes less than the resting potential and nerve can fire again; relative- refractory period K + channels close and action potential enters the absolute refractory period. Na K pump restores the resting potential during repolarization..