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': 'Which of the following normally has a slowly depolarizing “prepotential” \nSelect and explain. \nA. Sinoatrial node, B. Atrial muscle cells, C. Bundle of His, D. Purkinje fibers', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Rhythmically discharging cells have a membrane potential that, after each impulse, declines to the firing level. Thus, this prepotential or pacemaker potential triggers the next impulse.', 'role': 'assistant'}]