What does action potential cause in muscle fibers?

When an action potential is propagated along a muscle fiber, it initiates crucial physiological changes that ultimately lead to muscle contraction. The action potential travels along the sarcolemma (the muscle cell membrane) and into the interior of the muscle fiber through structures called T tubules. This process is known as T tubule depolarization.

As the action potential intensifies over the membrane and reaches the T tubules, it triggers the opening of voltage-gated calcium channels in the sarcoplasmic reticulum (the muscle fiber's internal calcium storage). The subsequent release of calcium ions from the sarcoplasmic reticulum into the cytoplasm is a key event that elevates intracellular calcium levels, facilitating muscle contraction through a series of interactions between actin and myosin filaments.

The other options, while relevant to broader physiological processes, do not accurately reflect the direct consequence of action potential in muscle fibers. Increased blood flow is typically a response to muscle activity rather than a direct outcome of an action potential. The release of hormones is a systemic response mediated primarily by endocrine functions, and muscle fiber contraction, while eventually resulting from action potentials, is not the immediate effect; the immediate effect is the depolarization of T tubules that leads to the contraction process