Resting membrane potential

- is expressed as the measured potential difference across the cell membrane in millivolts (mV).

-is, by convention, expressed as the intracellular potential relative to the extracellular potential. Thus, a resting membrane potential of -70 mV means 70 mV, cell negative.

1. The resting membrane potential is established by diffusion potentials that result from concentration differences of permeant ions.

2. Each permeable ion attempts to drive the membrane potential toward its equilibrium potential. Ions with the highest permeabilities, or conductances, will make the greatest contributions to the resting membrane potential, and those with the lowest permeabilities will make little or no contribution.

3. For example, the resting membrane potential of nerve is -70 mV, which is close to the calculated K+ equilibrium potential of -85 mV, but far from the calculated Na+ equilibrium potential of +65 mV. At rest, the nerve membrane is far more permeable to K+ than to Na+.

4. The Na+-K+ pump contributes indirectly to the resting membrane potential by maintaining, across the cell membrane, the Na+ and K+ concentration gradients that then produce diffusion potentials. The direct electrogenic contribution of the pump (because it pumps 3 Na+ out of the cell for every 2 K+ pumped into the cell) is small.

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