This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Spike in action potential of a nerve is due to which ions 
Select and explain. 
A. K+, B. Na+, C. Cl-, D. All of the above
B: Na+
Answer: B: Na+ 
Explanation: Na+ enters the nerve cell and K+ leaves it during the action potential, the number of ions involved is minute relative to the total numbers present. (Ref: Ganong&;s review of medical physiology; 23rd edition; pg: 85)