How can an impulse be passed along a membrane?

The resting membrane is polarized, meaning the interior is –70 mV/negative relative to the outside. In this state more sodium ions (Na+) are outside the cell than inside. In contrast, more potassium ions (K+) are inside than outside.

A disturbance of the membrane opens sodium ion channels and sodium ions rush to the inside of the cell causing depolarization. Then, sodium ion channels shut and potassium ion channels open causing potassium ions to rush out and helping to restore the polarized state of membrane. This entire process is called an action potential. Sodium–potassium pumps then maintain polarity.

This process is repeated along the length of a neuron. Sodium ions diffuse between regions with an action potential and the region at resting potential.

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