This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
[{'content': 'SA node acts as a pacemaker of the heart because of the fact that it: \nSelect and explain. \nA. Is capable of generating impulses spontaneously, B. Has rich sympathetic innervations, C. Has poor cholinergic innervations, D. Generates impulses at the highest rate', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. D. Generates impulses at the highest ratea. The various parts of the conduction system of heart and, under abnormal conditions, parts of the myocardium are capable of spontaneous discharge.b. However, the SA node normally discharges most rapidly, depolarization spreading from it to the other regions before they discharge spontaneously.c. The SA node is therefore the normal cardiac pacemaker, its rate of discharge determining the rate at which heart beats.', 'role': 'assistant'}]