The action potential is a rapid and reversible reversal of the electrical potential difference across the plasma membrane of excitable cells such as neurons, muscle cells and some endocrine cells. In a neuronal action potential, the membrane potential rapidly changes from its resting level of approximately -70 mV to around +50 mV and, subsequently, rapidly returns to the resting level again. The neuronal action potential forms an important basis for information processing, propagation, and transmission. In muscle cells, the action potential precedes, and is necessary to bring about, muscle contraction. Some endocrine cells also exhibit action potentials, where the excitation leads to hormone secretion.

The action potential is also referred to as the electrical impulse or nervous impulse.

Graded potential

Neuronal Action Potential

Electrochemical gradient

Electrochemical gradient

The voltage difference across a cell plasma membrane.

The membrane potential is generally inside negative with respect to the outside, where the outside potential is generally set as the reference value. In electrically excitable cells, the value of the membrane potential can be positive (inside with respect to the outside) during electrical activity (i.e., during action potentials).

Resting membrane potential

Resting membrane potential

The voltage difference across a cell plasma membrane in the resting or quiescent state. It is also simply referred to as the resting potential (V_rest). The value of the resting membrane potential varies from cell to cell. Depending on the cell type, it can range from −90 mV to −20 mV.

For example, V_rest is −90 mV in skeletal and cardiac muscle cells as well as in astrocytes. In a typical neuron, V_rest is approximately −70 mV. In many non-excitable cells, V_rest ranges from −60 to −50 mV. In photoreceptors, V_rest is about −20 mV.

Resting membrane potential

The difference in electrical potential between two points.