During the course of an action potential, the membrane potential rapidly rises and reaches a peak of about + 40 mV before falling to about - 75 mV. What causes the fall in membrane potential?

A) A decrease in Na + permeability, and an increase in K + permeability

B) A decrease in the permeability to both Na + and K+

C) An increase in Na + permeability, and a decrease in the K + permeability

D) An increase in the permeability to both Na and K

Question

Biology

Frank Dunn

30 October, 21:30

During the course of an action potential, the membrane potential rapidly rises and reaches a peak of about + 40 mV before falling to about - 75 mV. What causes the fall in membrane potential?

A) A decrease in Na + permeability, and an increase in K + permeability

B) A decrease in the permeability to both Na + and K+

C) An increase in Na + permeability, and a decrease in the K + permeability

D) An increase in the permeability to both Na and K

+1

Answers (1)

Know the Answer?

Conor Hawkins · Answer 1

A) A decrease in Na + permeability, and an increase in K + permeability.

Explanation:

When the potential action reaches a peak of about + 40 mv Na + channels are open and a high number of Na + ions are entering the inside of the cell. Shortly after this happens the K + channels will start to open their gates increasing the cell K + permeability while the Na + channels will start to close their gates, so the Na + permeability will decrease. This happens in order to valance the positive charge on the inside of the cell. Normally the inside has a negative charge while the outside has a positive one, as the inside is more positive due to the increase in Na + permeability at the beginning of the potential action, K + cations (which are in abundance in the cell) will have to go out through the K + channels so as to restore the charge valance, that means that there is an increase in K + permeability.