Question

The concentration of sodium is greater in the extracellular fluid compared to the intracellular fluid. If the membrane potential was equal to the equilibrium potential for sodium, then what would be the direction of the electrochemical force acting on sodium?

A) inward

B) outward

C) equal in both directions

D) varies by cell

E) varies based on concentration of potassium in the intracellular and extracellular fluids

Answer 1

A) inward

The direction of the electrochemical force on sodium would be inward if the membrane potential were not at equilibrium, due to the higher concentration of sodium in the extracellular fluid and the negative charge inside the cell.

Step-by-step explanation:

If the membrane potential was equal to the equilibrium potential for sodium, then there would be no net movement of sodium ions across the membrane because the electrical force counterbalances the chemical force due to concentration difference. However, since the concentration of sodium is greater in the extracellular fluid compared to the intracellular fluid, if we were not at equilibrium, the electrochemical force would act to move sodium inward (answer A).

This is because the concentration gradient would drive sodium to move down its concentration gradient into the cell, combined with the electrical gradient because the inside of the cell is usually negatively charged relative to the outside.