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# Calculation: Equilibrium Potential

NEURO-$W8EAB At the equilibrium potential of an ion, there is no net flow of that particular ion across the membrane. The equilibrium potential of an ion can be calculated with the Nernst equation${ E }_{ ion }=2.303\times \frac { RT }{ zF } \log { \frac { { \left[ ion \right] }_{ out } }{ { \left[ ion \right] }_{ in } } } $. In this equation, R is gas constant, T is absolute temperature, z is the charge of the ion, F is Faraday’s constant. The second fraction is the extracellular concentration of that ion over the intracellular concentration. Based on the table of a typical neuronal membrane provided here, which of the following statements is CORRECT? Ion Concentration outside (in mM) Concentration inside (in mM) Ratio Out : In${ K }^{ + }$5 100 1 : 20${ Na }^{ + }$150 15 10 : 1${ Ca }^{ 2+ }$2 0.0002 10,000 : 1${ Cl }^{ - }$150 13 11.5 : 1 A Increasing the intracellular concentration of${ Na }^{ + }$would make${ E }_{ Na }$more positive. B${ E }_{ Cl }$is the most negative equilibrium potential. C${ E }_{ Na }$> 0 >${ E }_{ K }$. D${ E }_{ Na }\$ is the most positive equilibrium potential.