17 The resting membrane potential
Membrane potential
All cells have an electrical potential difference across their plasma membrane (membrane potential). This is always expressed as the voltage inside relative to that outside the cell. Animal cells have resting membrane potentials ranging from approximately −20 to −90 mV depending on the cell type (Fig. 3.17.1). Changes in this potential difference form the basis of electrical signalling in cells.
The resting membrane potential
At rest, cell membranes are more permeable to K+ than to other ionic species because of facilitated diffusion through K+ channel proteins, which form K+-specific pores in the membrane. The extracellular and intracellular K+ concentrations in a ‘typical’ cell are 4.5 and 160 mmol/l, respectively; therefore, K+ tends to move outwards down its concentration gradient. Since large protein anions inside the cell are unable to follow K+
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