During an action potential, the movement of ions across the membrane involves:

1. At rest, sodium is more concentrated outside the cell and potassium more concentrated inside. 2. When the threshold of excitation is reached, many pores open and sodium rushes into the cell, producing a large positive spike. 3. At the peak of the action potential the sodium gates close and the potassium gates open, so potassium leaves the cell. 4. That outflow repolarises the membrane, briefly overshooting into hyperpolarization before settling back to the resting potential. _Source: OpenStax Psychology (1st ed., CC BY 4.0), Ch 3 "Biopsychology", §3.2 Cells of the Nervous System_