Resting membrane potential

The resting membrane potential is the voltage difference across the plasma membrane of a cell that is not sending a signal. It is given as the inside relative to the outside, and in a typical neuron it is about -70 millivolts (mV), though the value differs between cell types, ranging from roughly -30 to -100 mV in excitable cells. Every cell has one, but it matters most in neurons and muscle cells, whose signals are brief changes in it.

Two things create it. The sodium–potassium pump keeps potassium concentrated inside the cell and sodium concentrated outside. At rest the membrane is far more permeable to potassium than to sodium, because many potassium leak channels are open. Potassium ions therefore drift outward down their concentration gradient, leaving behind negatively charged proteins and other anions, until the growing negative charge inside holds them back. The resting potential ends up near the equilibrium potential for potassium, made slightly less negative by a small inward leak of sodium. The Nernst and Goldman equations let students calculate these values.

A stimulus that makes the inside less negative, called depolarization, can reach threshold and fire an action potential. Abnormal blood potassium shifts the resting potential, which is why it can disturb heart rhythm.