The difference in electrical charge across the plasma membrane of a cell due to differences in the distribution of charged ions between the interior of the cell and the extracellular fluid. Membrane potentials exist in all living cells, and typically are in the range –20 to –200 mV. Examples include neuron, –70 mV; skeletal muscle cell, –90 mV; smooth muscle cell, –50 mV; plant root or stem cells, –100 to –130 mV. See resting potential.