Final answer:
All statements are true concerning an action potential; it involves voltage-gated Na+ channels, is triggered at a threshold, and exhibits an all-or-none response.
Step-by-step explanation:
The correct answer to the student's question, "Which of the following is true of an action potential?" is: 4) All of these answers are correct. Each of the statements provided is a key aspect of the physiological process of an action potential.
An action potential is indeed generated through the action of voltage-gated Na⁺ channels. These channels are crucial for the rapid influx of sodium ions that depolarize the neuron's membrane. A stimulus must bring the membrane potential to the threshold of excitation, approximately -55 mV, to trigger these channels to open. The all-or-none nature of an action potential means that once the threshold is reached, there is a full response, and the magnitude of the action potential is independent of the intensity of the stimulus as long as the threshold is reached.
During an action potential, depolarization occurs as Na⁺ ions enter the neuron, reversing the charge across the membrane. This is then followed by repolarization, where K⁺ ions exit the neuron, and the Na⁺ channels close. Hyperpolarization often occurs temporarily as the channels take time to reset to their resting state, and during this time the neuron is less likely to fire another action potential. Active transport mechanisms like the Na⁺/K⁺ pump help to restore and maintain the resting membrane potential. Overall, this complex sequence ensures that neurons can rapidly fire multiple action potentials to transmit signals throughout the nervous system.