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NEURONAL RESTING POTENTIAL


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NEURONAL RESTING POTENTIAL
Cations (+) and anions (−) are distributed unevenly across the neuronal cell membrane because the membrane is differentially permeable to these ions. The uneven distribution depends on the forces of charge separation and diffusion. 

NEURONAL RESTING POTENTIAL

The permeability of the membrane to ions changes with depolarization (toward 0) or hyperpolarization (away from 0). The typical neuronal resting potential is approximately −90 mV with respect to the extracellular fluid. The extracellular concentrations of Na+ and Cl of 145 and 105 mEq/L, respectively, are high compared to the intracellular concentrations of 15 and 8 mEq/L. The extracellular concentration of K+ of 3.5 mEq/L is low compared to the intracellular concentration of 130 mEq/L. The resting potential of neurons is close to the equilibrium potential for K+ (as if the membrane were permeable only to K+). Na+ is actively pumped out of the cell in exchange for inward pumping of K+ by the Na+-K+-ATPase membrane pump. Equivalent circuit diagrams for Na+, K+, and Cl, calculated using the Nernst equation, are illustrated in the lower diagram.