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
[{'content': 'Action potential is initiated at the axon hillock/initial segment of neuron because: \nSelect and explain. \nA. 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', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Because the initial segment of the axon has the highest density of voltage\xad sensitive Na+\xa0channels and therefore the lowest threshold for generating an action potential.', 'role': 'assistant'}]