This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'Action potential is initiated at the Axon Hillock - Initial segment of the 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 sodium channels', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The axon hillock contains the highest density of Na+-VGCs.....Hence it is a low threshold trigger zone. Synaptic input located close to the trigger zone is more effective in depolarizing and hyperpolarizing it than synaptic inputs of equal strength located fuher away. Ref guyton and hall textbook of medical physiology 12/e pg 543 and 59', 'role': 'assistant'}]