This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which event will NOT occur during depolarization phase? 
Select and explain. 
A. Na+ channels open, B. Ca+ channels open, C. K+ channels open, D. None of the above
C: K+ channels open
Answer: C: K+ channels open 
Explanation: Na+ channels open, increasing the permeability of the cell membrane to Na+. Sodiumions then diffuse into the cell, causing depolarization. This causes K+ channels to close quickly, decreasing the permeability of the cell membrane to K+. The decreased diffusion of K+out of the cell also causes depolarization. Ca2+ channels slowly open, increasing the permeability of cell membrane to Ca2+. Calcium ions then diffuse into the cell and cause depolarization.