A separation of oppositely charged ions across the plasma membrane of a cell. The sign of the voltage represents the charge inside of the cell. If membrane potential = +30 mv, it is more positive inside of the cell. Creates a concentration gradient for na+ and k+ K+ is pumped into the cell while na+ is pumped out of the cell. Leak channels are channels for specific ions (na+ or k+) that are always open, allowing these ions to leak across the membrane, creates a resting membrane potential. There are more leak channels for k+ than na+, leaving the inside of the cell more negative. The typical value of resting membrane potential is -70 mv. Resting membrane potential is a dynamic steady state. If the membrane potential becomes more negative than -70 mv, it is hyperpolarized. If the membrane potential becomes more positive than -70 mv, it is depolarized. Occurs when a stimulus causes gated channels to open or close.