Draw a graph showing what would happen to resting membrane potential over time, if the sodium/potassium pump were not functioning. How would this affect a neuron's ability to produce action potentials? What does this imply about the quantity of ions that normally cross the membrane during the course of an action potential?

Question

What will be an ideal response?

Answer 1

It would be appropriate for the student to draw action potentials on the graph beginning at the point where the resting potential drifts up to threshold, and decreasing in frequency a s the resting potential approaches. Very gradually, a cell's resting membrane potential would increase until it reached and stabilized there. At that point the ions would be in equilibrium, and no further net flow of charge would occur. There would be no effect on ability to generate action potentials initially, but with the disappearance of the differential distribution of sodium and
potassium upon which the action potential depends, action potentials would gradually come to a stop. This points out the fact that during any single action potential, so few ions cross the membrane that there is no significant
change in ion concentrations. Thousands of action potentials would be required before the absence of the
sodium-potassium pumps would be noticeable.