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: Physiology
Action potential is initiated at the axon hillock/initial segment of neuron because: 
Select and explain. 
A. Threshold for excitation is lowest, B. Neurotransmitter is released at this site, C. It is an unmyelinated segment, D. Has lowest concentration of voltage gated Na+  channel
A: Threshold for excitation is lowest
Answer: A: Threshold for excitation is lowest 
Explanation: Because the initial segment of the axon has the highest density of voltage­ sensitive Na+ channels and therefore the lowest threshold for generating an action potential.