During the repolarization phase of an action potential which of the following is the primary activity in the membrane of the post-synaptic cell?
A) Sodium ions are flowing out of the cell.
B) Sodium ions are flowing into the cell.
C) Potassium ions are flowing into the cell.
D) Potassium ions are flowing out of the cell.
Answer:
D) Potassium ions are flowing out of the cell.
Explanation:
The threshold opens both voltage-gated Na+ channels and the voltage-gated K+ channels. The voltage-gated K+ channels are very slow in opening. Therefore, they open when the voltage-gated Na+ channels are closing. The opened voltage-gated K+ channels are responsible for the repolarizing phase.
During this phase, the inflow of Na+ becomes less as the responsible channels are inactivated. The opened K+ channels allow the K+ to move out of the post-synaptic cell. It results in the generation of negative charge inside the cell membrane as the membrane potential reduces +30 mV to −70 mV.
