This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nerve, Subject name: Physiology
[{'content': 'Refractory period of a myelinated nerve is due to: \nSelect and explain. \nA. Voltage-dependence of Na+ channels, B. Time-dependence of Na+ channels, C. Voltage-dependence of K+ channels, D. Time-dependence of K+ channels', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Only when the membrane has repolarized up to about - 40 mV to - 50 mV that the Na+ channels recover from their inactivated state and go into resting state. All this while, the membrane is refractory; that is, the membrane can excite again only when many of the Na+ channels have recovered (which itself depends on the membrane potential). Hence, refractory period is due to the voltage-dependance of the Na+ channels.', 'role': 'assistant'}]