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': 'Repolarization of a nerve is due to: September 2009 \nSelect and explain. \nA. Hydrogen ions, B. Potassium ions, C. Sodium ions, D. Calcium ions', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B: Potassium ionsThe Na+ channels rapidly enter the inactivated state and remain in this state for a few milliseconds before returning to the resting state. In addition, the direction of the electrical gradient for Na+ is reversed during the overshoot because the membrane potential is reversed, and this limits Na+ influx.A third factor producing repolarization is the opening of voltage-gated K+ channels.The net movement of positive charge out of the cell due to K+ efflux at this time helps complete the process of repolarization.The slow return of the K+ channels to the closed state also explains the after-hyperpolarization.', 'role': 'assistant'}]