🧪 General Principles🟢 BasicCell Membrane Physiology

The Resting Membrane Potential

The steady electrical voltage across the membrane of a resting cell, set up mainly by potassium, which nerve and muscle cells use as their starting point.

Key points

Most living cells have a voltage across the membrane, the inside negative compared with the outside; the familiar value of about minus seventy millivolts is a typical nerve/muscle figure and varies between cell types.
It arises because the membrane at rest is far more leaky to potassium than to sodium, so potassium leaving the cell down its gradient sets the voltage.
The gradients themselves are built and maintained by the sodium-potassium pump, which pushes sodium out and potassium in using ATP.
The pump is also slightly electrogenic, moving three sodium out for two potassium in, which adds a little to the negativity inside the cell.
The Nernst equation predicts the voltage at which a single ion would be balanced; the resting potential lies close to, but not exactly at, the potassium value because the membrane is also slightly permeable to sodium.
Changing the outside potassium level therefore strongly affects excitable cells, which is why a high blood potassium is dangerous to the heart.

Memory trick

Potassium sets the rest: a leaky-to-potassium membrane makes the inside about minus seventy millivolts; the sodium-potassium pump keeps the gradients that make it possible.

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🧪 General Principles🟢 BasicCell Membrane Physiology

The Resting Membrane Potential

The steady electrical voltage across the membrane of a resting cell, set up mainly by potassium, which nerve and muscle cells use as their starting point.

Key points

Most living cells have a voltage across the membrane, the inside negative compared with the outside; the familiar value of about minus seventy millivolts is a typical nerve/muscle figure and varies between cell types.
It arises because the membrane at rest is far more leaky to potassium than to sodium, so potassium leaving the cell down its gradient sets the voltage.
The gradients themselves are built and maintained by the sodium-potassium pump, which pushes sodium out and potassium in using ATP.
The pump is also slightly electrogenic, moving three sodium out for two potassium in, which adds a little to the negativity inside the cell.
The Nernst equation predicts the voltage at which a single ion would be balanced; the resting potential lies close to, but not exactly at, the potassium value because the membrane is also slightly permeable to sodium.
Changing the outside potassium level therefore strongly affects excitable cells, which is why a high blood potassium is dangerous to the heart.

Memory trick

Potassium sets the rest: a leaky-to-potassium membrane makes the inside about minus seventy millivolts; the sodium-potassium pump keeps the gradients that make it possible.

All of Physiology More General Principles