Question

The rising phase of the action potential is due to?

1) Na⁺ flow out of the cell and K⁺ flow into the cell
2) K⁺ flow out of the cell only
3) Na⁺ flow out of the cell only
4) K⁺ flow into the cell only
5) Na⁺ flow into the cell only

Answer 1

The rising phase of the action potential is due to the influx of sodium (Na⁺) ions into the cell only. This depolarizes the neuron's membrane and is critical for the initiation of an action potential. The correct answer is 5) Na⁺ flow into the cell only.

Step-by-step explanation:

The rising phase of the action potential is due to sodium (Na⁺) ions flowing into the cell. This occurs when a stimulus causes the membrane to become permeable to Na⁺ ions, leading to depolarization as the membrane potential rapidly becomes less negative. During the rising phase, there is a sudden influx of Na⁺ ions into the neuron, resulting from the opening of voltage-gated Na⁺ channels, which is essential for the initiation of an action potential.

The correct choice is 5) Na⁺ flow into the cell only. This influx of Na⁺ leads to rapid depolarization of the neuron's membrane. Potassium ions (K⁺) play a role in the repolarization phase, where they flow out of the cell to help return the membrane to its resting potential after the peak of the action potential is reached. This process is crucial for the cell to become ready for another action potential.