The repolarization phase of an action potential is due to: (A) Increasing sodium permability and increasing potassium permeability, (B) Increasing sodium permeability and decreasing potassium permeability, (C) Decreasing sodium permeability and an immediate increasing potassium permeability, (D) Decreasing sodium permeability and a delayed increase potassium permeability
Answer is D. There is a decrease in sodium permeability (inactivation of the sodium channels) and a delayed increased in potassium permeability during the repolarization phase of the action potential. The pump plays no direct role in the action potential.