Glossary of Physiology Terms

Action potential

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

P wave

The component of the electrocardiogram (ECG) that corresponds to the depolarization of atrial myocytes. Atrial depolarization precedes atrial contraction.

QRS complex
T wave

QRS complex

The component of the electrocardiogram (ECG) that corresponds to the depolarization of ventricular myocytes. Ventricular depolarization precedes ventricular contraction.

P wave
T wave