All cells (including neurons) have resting membrane potentials. The ionic environment inside a cell differs from the ionic environment outside the cell. This difference is maintained by special ion pumps that are embedded in the cell membrane. Because the ions have a charge (cations are positively charged and anions are negatively charged), this difference in ionic content sets up an electrical potential difference between the interior and the exterior of the cell. Excitable cells (e.g., neurons, cardiac muscle cells, and striated muscle cells) also have other ion channels across the cell membrane that can be activated (or gated) by different conditions. For a neuron, this potential difference produced by the ion pumps when the cell is “at rest” is called the “resting membrane potential.”

The resting membrane potential of an average neuron is approximately –70 millivolts with respect to the exterior of the cell. This means that the electrical charge on the inside of the plasma membrane measures 0.07 volts less than that on the outside of the plasma membrane.