Question

Which of the following is true about threshold for an action potential? A) It is more positive than the resting membrane potential. B) Voltage-gated potassium channels begin to close. C) Voltage-gated potassium channels begin to open. D) The membrane begins to hyperpolarize. E) Threshold for a typical neuron is approximately -30 mV.

Answer 1

The true statement about the threshold for an action potential is that it is more positive than the resting membrane potential (option A). This threshold triggers the opening of voltage-gated Na+ channels leading to depolarization of the neuron and the initiation of an action potential. Following depolarization, voltage-gated K+ channels open for repolarization.

Step-by-step explanation:

The correct answer to the question "Which of the following is true about threshold for an action potential?" is A) It is more positive than the resting membrane potential. When a neuron is stimulated and the membrane potential reaches the threshold, usually around -55 mV, the voltage-gated Na+ channels open, allowing positive ions to enter the cell and causing depolarization. This depolarization flips the membrane potential from around -70 mV to approximately +30 mV. The action potential is an all-or-nothing event, meaning that once the threshold potential is reached, the neuron will always completely depolarize.

Following depolarization, voltage-gated K+ channels open, allowing potassium ions to leave the cell, which begins the process of repolarization. This brings the membrane potential back towards the resting potential. Soon after, the K+ channels close, and the membrane potential returns to its resting state. The overshoot during this process can result in a hyperpolarized state before the resting potential is stabilized. The neuron goes through a refractory period during which another action potential cannot be initiated.