Okn

The Na+-K+ also causes large concentration gradients for sodium and potassium across the resting nerve membrane. These gradients are the following:

The ratios of these two respective ions from the inside to the outside are

Na+inside/Na+outside = 0.1

inside'^- outside JJ.VJ

Leakage of Potassium and Sodium Through the Nerve Membrane. The right side of Figure 5-4 shows a channel protein in the nerve membrane through which potassium and sodium ions can leak, called a potassium-sodium (K+-Na+) "leak" channel. The emphasis is on potassium leakage because, on average, the channels are far more permeable to potassium than to sodium, normally about 100 times as permeable. As discussed later, this differential in permeability is exceedingly important in determining the level of the normal resting membrane potential.

Origin of the Normal Resting Membrane Potential

+-Diffusion

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