Resting Potential Note

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The inside of the neurone is negatively charged relative to the outside because of an unequal distribution of charged ions.

On the outside being Na+, Cl- and Ca2+ and the inside K+ and organic anions.

This unequal distribution arises because of the active transport and diffusion of sodium and potassium across the cell membrane and the inability of large organic anions to pass through.

A sodium-potassium pump actively transports Na+ out of the neurone and K+ in.

FOR EVERY THREE NA+ PUMPED OUT, ONLY TWO K+ ARE PUMPED IN.

On its own this would only result in a small potential difference but this difference is amplified by the membrane being about 50 times more permeable to K+ than to Na+. Also, inside the membrane there are large organic anions in the cytoplasm hence a negative potential is maintained inside the neurone.

K+ ions can diffuse freely out of the cell down their own concentration gradient but Na+ gated channels are closed.

Thi

N. B MEMBRANE IS POLARISED. (-60MV) (i.e interior negative, outside positive)

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