Page "Resting potential" Paragraph 3

Any voltage is a difference in electric potential between two points-for example, the separation of positive and negative electric charges on opposite sides of a resistive barrier.

The typical resting membrane potential of a cell arises from the separation of potassium ions from intracellular, relatively immobile anions across the membrane of the cell.

Because the membrane permeability for potassium is much higher than that for other ions ( disregarding voltage-gated channels at this stage ), and because of the strong chemical gradient for potassium, potassium ions flow from the cytosol into the extracellular space carrying out positive charge, until their movement is balanced by build-up of negative charge on the inner surface of the membrane.

Again, because of the high relative permeability for potassium, the resulting membrane potential is almost always close to the potassium reversal potential.

But in order for this process to occur, a concentration gradient of potassium ions must first be set up.

This work is done by the ion pumps / transporters and / or exchangers and generally is powered by ATP.