opened under specific circumstances for a few microseconds at a time. This allows a brief inflow of sodium ions into the cell (driven in by the sodium ion concentration gradient that exists between the outside and inside of the cell). This causes the cell membrane to temporarily depolarize (lose its electrical charge) forming the basis of action potentials.

The sodium ions in the ECF also play an important role in the movement of water from one body compartment to the other. When tears are secreted, or saliva is formed, sodium ions are