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
A traveling nerve impulse does not depolarize the area immediately behind it, because: 
Select and explain. 
A. It is hyperpolarised, B. It is refractory, C. It is not self-propagating, D. The conduction is always ohodromic
B: It is refractory
Answer: B: It is refractory 
Explanation: When an AP is initiated at a point, the point goes into refractoriness when the Na+ entered through that point has excited the adjacent (2nd) point. so it will travel in single direction Hyperpolarization event is after the refractory period.