What causes the undershoot phase of the action potential?
Select one
a. Voltage-gated potassium channels close slowly, thus prolonging potassium-caused hyperpolarization.
b. There is more potassium than sodium, so there is a larger efflux of potassium than influx of sodium, causing the negative membrane potential.
c. the Na+/K+ pump
d. If you have an overshoot, you’ve gotta have an undershoot-just the way life works.
The Correct Answer and Explanation is :
The correct answer is:
a. Voltage-gated potassium channels close slowly, thus prolonging potassium-caused hyperpolarization.
Explanation:
The undershoot phase of the action potential, also known as the afterhyperpolarization, occurs after the repolarization phase of the action potential. During an action potential, the membrane potential rises sharply due to the influx of sodium ions through voltage-gated sodium channels, leading to depolarization. Once the membrane potential reaches its peak, sodium channels close, and voltage-gated potassium channels open, allowing potassium ions (K+) to flow out of the cell. This efflux of potassium causes the membrane potential to become more negative, resulting in repolarization.
However, the undershoot happens because the voltage-gated potassium channels close slowly after repolarization. As a result, potassium continues to flow out of the cell for a brief period, making the inside of the cell more negative than the resting membrane potential. This hyperpolarization is called the undershoot, and it is a consequence of the potassium channels’ delayed closure.
The Na+/K+ pump (choice c) plays a role in maintaining the resting membrane potential by actively transporting sodium out and potassium into the cell, but it is not responsible for the undershoot phase. The pump works continuously to restore ionic gradients but does not directly contribute to the undershoot.
To summarize, the undershoot phase results from the slow closure of voltage-gated potassium channels, leading to an extended potassium efflux and a more negative membrane potential than at rest.
I’ll also generate an image to visualize the action potential, including the undershoot phase.
Here is a diagram illustrating the action potential, showing the phases of depolarization, repolarization, and the undershoot phase. This image highlights the flow of ions and the changes in membrane potential during these phases. Let me know if you need further clarification!
