This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Excitation and Action Potiential, Subject name: Physiology
The phase of after depolarization is characterized by: 
Select and explain. 
A. Delayed entry of Na+, B. Na+ influx above zero potential, C. Slow closure of K+ channels, D. Slower net exit of K+
D: Slower net exit of K+
Answer: D: Slower net exit of K+ 
Explanation: The slower rate of repolarization toward the later pa has been described as After depolarization. The initial rate of repolarization is rapid. This is due to a greater concentration gradient for K+ to move out. However, as the K+ moves out, two things happen: Concentration gradient for K+ will narrow. Thus, rate of K+ efflux will decrease. The K+ that moved out will cause accumulation of positive charges (carried by K+) just on the outside of the membrane.