Question

In the early stage of repolarization, the sarcolemma is restored to its initial polarized state initially by

a. Na+
b. acetylcholine
c. Cl-
d. Ca2+ diffusing rapidly out of the muscle fiber
e. K+ diffusing rapidly out of the muscle fiber.

Answer 1

During the early stage of repolarization in muscle fibers, the restoration of the sarcolemma to its initial polarized state is primarily facilitated by the rapid diffusion of potassium ions (K+) out of the muscle fiber.

Thus the correct option is e.

Explanation

During the early stage of repolarization in muscle fibers, the restoration of the sarcolemma to its initial polarized state is primarily facilitated by the rapid diffusion of potassium ions (K+) out of the muscle fiber.

At the end of the action potential, voltage-gated potassium channels open, allowing K+ ions to move down their electrochemical gradient, exiting the cell. This efflux of positively charged potassium ions helps re-establish the negative resting membrane potential by reducing the positive charge inside the cell.

As K+ moves out, the interior of the cell becomes more negative, restoring the electrical balance necessary for subsequent muscle contractions. Other ions like Na+ and Ca2+ are involved in different stages of the action potential, but during repolarization, it's predominantly the outward movement of K+ that plays the key role in returning the membrane potential to its polarized state. This process is essential for the muscle cell to reset and prepare for subsequent excitation.

Thus the correct option is e.

Answer 2

During the early stage of repolarization, voltage-gated potassium channels open, allowing potassium ions to move out of the cell. This efflux of K+ ions restores the sarcolemma to its initial polarized state.Thus the correct option is e.

Step-by-step explanation:

In the early stage of repolarization, the sarcolemma is restored to its initial polarized state primarily through the efflux of potassium ions (K+). The repolarization phase follows the depolarization phase during an action potential in muscle cells. When the voltage-gated potassium channels open, K+ ions move out of the cell, leading to a restoration of the negative membrane potential.

During the action potential, voltage-gated sodium (Na+) channels open, causing a rapid influx of sodium ions, which results in depolarization. As the membrane potential becomes positive, voltage-gated potassium channels open, allowing K+ ions to move out of the cell. This efflux of K+ ions helps to re-establish the negative resting membrane potential, bringing the sarcolemma back to its polarized state.

The movement of ions during repolarization is essential for the proper functioning of excitable cells like muscle fibers. Understanding the dynamics of ion movement, particularly the role of potassium ions in repolarization, is crucial for grasping the physiological processes underlying muscle cell action potentials. The balance of ion movements ensures the proper sequence of events in muscle contraction and relaxation, contributing to the overall functionality of the muscular system.

Therefore the correct option is e.