Ion concentrations in the intracellular fluid and extracellular solution.

The Na⁺/K⁺-ATPase, also known as the Na⁺-K⁺ pump, is essential for maintaining the resting state of a nerve cell. Every cell has a membrane separating the intracellular fluid from the extracellular solution. When a nerve cell is at rest, the membrane voltage (or called membrane potential) is about -70mV (intracellular side relative to the extracellular side). The concentration of sodium (Na⁺) ions in the extracellular solution is much higher than inside. Therefore, Na⁺ ions will move inward due to both electric potential and ion concentration differences. The concentration of potassium (K⁺) ions in the extracellular solution is lower than inside. The combined effect of the electric potential and ion concentration differences makes the K⁺ ions move outward. The inward Na⁺ current is slightly greater than the outward K⁺ current.

In a normal cell, the resting state is maintained by the Na⁺/K⁺-ATPase which moves three Na⁺ ions out of the cell for every two K⁺ ions taken in. This active transport just balances the passive transport described above. If the enzyme loses its function, the cell will have only the passive transport where the inward Na⁺ current and the outward K⁺ current will cause the cell to lose their concentration differences. In addition, failure of the enzyme will cause the membrane voltage to become more positive than in the normal resting state (called "depolarized") because the inward Na⁺ current is greater than the outward K⁺ current.