What happens to potassium ions during muscle fiber activation by ACh?

During muscle fiber activation, acetylcholine (ACh) plays a critical role by binding to receptors on the muscle cell membrane, leading to changes in the membrane potential. This process initiates an influx of sodium ions into the muscle fiber, which depolarizes the membrane and triggers muscle contraction.

As a result of this depolarization and subsequent action potential, potassium ions, which are more concentrated inside the muscle fiber compared to the extracellular fluid, will diffuse out of the muscle fiber. This efflux of potassium helps to repolarize the membrane after the action potential, allowing the muscle fiber to return to its resting state. Therefore, the movement of potassium ions is essential for the proper functioning of muscle contractions and the restoration of the membrane potential after activation.

The correct answer reflects the dynamic balance and movement of ions that is crucial for muscle fiber excitation-contraction coupling.