The membrane potential rises toward zero, the voltage-regulated sodium channels begin closing which in turn reduces the sodium movement to the icf. with membrane potentials approaching 35 mv, the voltage-regulated potassium channels become fully activated. through the activated channels, potassium now flows outwards causing the membrane to repolarize back towards rmp. with a larger duration of activation than sodium channels, the potassium channels allow for a greater movement of potassium to the ecf causing a short period of hyperpolarization.