Sodium flow and the action potential

Sodium Ions () are at different concentrations outside (top) and inside (bottom) of the nerve cell. This maintains the resting voltage at -90 millivolts (mV). The inside is negative relative to the outside because sodium ions are positively charged and there's more of the positive charges on the outside. Please note that this is a simplified version of the events that lead to an action potential. Other ions and processes are involved, but this explanation covers most of the effect.

A stimulus (electrical or chemical) causes the sodium gates () to open and the ions begin to move in. This short-circutes the cell and the voltage drops, creating the action potential.

The sodium gates close as the nerve cell reached +20 mV. The sodium pump then switches from off () to on () and begins to pump the sodium ions to the outside of the cell. This causes the voltage to return to resting potential.

Here, the resting potential has been re-established.

The above diagram shows the whole series. Can you explain everything that is going on? Key: Positively-charged sodium ions (); Sodium gates (channels- ). Sodium pump (shut down- ) Sodium pump (running- )

The Sodium-Potassium Pump