Question

Assuming no change in either the internal or external calcium ion concentration, at what membrane potential would there be no net movement of calcium across the membrane?

1) -25 mV
2) -50 mV
3) 0 mV
4) +25 mV
5) +50 mV

Answer 1

The equilibrium potential for calcium ions is likely a positive value, considering the resting membrane potential of a cell is between -50 mV to -70 mV.

Step-by-step explanation:

The point at which there would be no net movement of calcium across the membrane, assuming no change in internal or external calcium ion concentration, is known as the equilibrium potential of calcium ions.

This potential is determined by the Nernst equation and is a function of the concentration gradient of the ion in question across the membrane and the charge on the ion. The resting membrane potential of most cells, including neurons, is typically between -50 mV and -70 mV.

At this potential, potassium ions tend to leave the cell, contributing to the negative interior. The resting potential is much more permeable to potassium ions than to sodium or calcium ions. Thus, calcium's equilibrium potential is usually much more positive compared to the typical resting membrane potential. When a cell depolarizes during an action potential, it becomes less negative, even reaching positive values due to the influx of sodium ions.