Which of the following best describes the role of voltage-gated sodium (Na^+) channels during the initiation of an action potential in a neuron?

• A. They close during depolarization to prevent Na^+ ions from entering the neuron.
• B. They open to allow potassium (K^+) ions to exit the neuron, causing hyperpolarization.
• C. They are responsible for the active transport of Na^+ and K^+ ions against their concentration gradients.
• D. They open in response to depolarization, allowing Na^+ ions to enter the neuron and further depolarize the membrane.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of an action potential in neurons. An action potential is a rapid change in the electrical charge across a neuron's membrane, which allows the neuron to transmit signals. It involves depolarization (making the inside of the neuron less negative) and repolarization (returning to the resting state).
2. Step 2: Learn about voltage-gated sodium (Na⁺) channels. These are specialized protein channels in the neuron's membrane that open or close in response to changes in membrane potential. They play a critical role in the initiation and propagation of action potentials.
3. Step 3: Recognize the role of Na⁺ channels during depolarization. When the membrane potential reaches a threshold level, voltage-gated Na⁺ channels open, allowing Na⁺ ions to flow into the neuron. This influx of positively charged ions further depolarizes the membrane, making it more positive.
4. Step 4: Differentiate the role of Na⁺ channels from other ion channels. For example, voltage-gated potassium (K⁺) channels open later during the action potential to allow K⁺ ions to exit the neuron, which helps repolarize the membrane. Na⁺ channels are specifically involved in the depolarization phase.
5. Step 5: Relate the correct answer to the mechanism of action. The correct answer states that voltage-gated Na⁺ channels open in response to depolarization, allowing Na⁺ ions to enter the neuron and further depolarize the membrane. This aligns with the biological process of action potential initiation.