Membrane potential

Membrane potential is the electrical potential difference between solutions separated by a membrane. It arises from unequal ion distributions and the membrane’s selective permeability to ions.

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Nernst equation: An equation relating an ion’s concentration ratio across a membrane to the voltage at which that ion is in electrochemical equilibrium. It predicts the equilibrium voltage produced by a concentration gradient for one permeant ion.
Electric potential: Potential energy per unit charge at a point in an electric field. A membrane potential is a difference in this quantity between two solutions.
Resting membrane potential: The relatively stable voltage across a cell membrane when the cell is not actively signaling. It is the standard cellular instance of a membrane potential.
Diffusion potential: An electrical potential difference generated when ions diffuse at different rates through a boundary. It is one mechanism that can produce a membrane potential, rather than a competing voltage concept.
Goldman–Hodgkin–Katz equation: An equation estimating membrane voltage from multiple ions’ concentration gradients and relative permeabilities. It extends the single-ion picture to membranes permeable to several ions.
Concentration gradient: A spatial change in the concentration of a substance. Ion gradients supply the chemical component of the force that redistributes charge.
Action potential: A rapid, temporary reversal of a cell’s membrane voltage that propagates along excitable membranes. Changes in ion permeability drive the voltage waveform in nerves and muscles.
Liquid junction potential: A voltage arising where electrolyte solutions of different composition meet and ions diffuse at unequal rates. It can resemble a membrane voltage but occurs at a solution junction without a selective membrane.
Donnan equilibrium: The unequal distribution of diffusible ions across a permeable barrier caused by trapped charged particles on one side. Impermeant charges can establish ion gradients and a voltage even without active transport.
Diffusion: The net movement of particles from regions of higher concentration to lower concentration through random motion. Diffusion carries ions down concentration gradients when the membrane permits passage.