The voltage across membranes of excitable cells (e.g. nervous system, muscles, heart, endocrine system) transiently changes, creating a pulse-like wave called an "action potential". The action potential serves as a major signal for the initiation of many cellular and intercellular processes. The canonical mathematical-physical model of the phenomenon was presented by Alan Hodgkin and Andrew Huxley in 1952 in a series of seminal papers , where membrane potenial dynamics is described in terms of voltage-dependent ionic conductance, dominated by four coupled ordinary differential equations. In the realization presented here, the action potential is trigerred by a short current stimulus. Shown are time evolutions of membrane voltage (blue trace) and conductance gates (, , and ).
Maximal conductances are 20, 12, and .1 for sodium, potassium, and leak, respectively. Nernst equilibrium potentials are 50, -90, and -60 for sodium, potassium, and leak, respectively. Membrane capacitance is set to 1.
 B. Hille, Ion Channels of Excitable Membranes, Sunderland, MA: Sinauer, 2001.
 A. L. Hodgkin and A. F. Huxley, "A Quantitative Description of Membrane Current and Its Application to Conduction and Excitation in Nerve," Journal of Physiology, 117,1952 pp. 500–544.