Which of the following scenarios is most likely to trigger an action potential in a neuron?

• A. A depolarization that brings the membrane potential to the threshold value
• B. A hyperpolarization that moves the membrane potential further from threshold
• C. A return of the membrane potential to the resting value after a previous action potential
• D. A small depolarization that does not reach the threshold

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of an action potential. An action potential is a rapid electrical signal that travels along the membrane of a neuron. It is triggered when the membrane potential reaches a specific threshold value, typically due to depolarization.
2. Step 2: Define depolarization and hyperpolarization. Depolarization refers to a decrease in the difference in charge across the neuron's membrane, making the inside less negative relative to the outside. Hyperpolarization, on the other hand, increases this difference, making the inside more negative.
3. Step 3: Analyze the threshold concept. The threshold is the critical membrane potential value that must be reached for voltage-gated ion channels to open, initiating an action potential. If the membrane potential does not reach this threshold, no action potential will occur.
4. Step 4: Evaluate each scenario provided in the question. A depolarization that brings the membrane potential to the threshold value is most likely to trigger an action potential because it meets the necessary condition for initiating the signal. Hyperpolarization moves the membrane potential further from the threshold, making it less likely to trigger an action potential. Returning to the resting potential after a previous action potential does not trigger a new action potential. A small depolarization that does not reach the threshold is insufficient to initiate an action potential.
5. Step 5: Conclude that the scenario most likely to trigger an action potential is the depolarization that brings the membrane potential to the threshold value, as this is the physiological requirement for the initiation of an action potential.