Question

Which of the following temporal sequences is correct for excitation-contraction coupling in skeletal muscle?

1) Increased intracellular [Ca₂⁺]; action potential in the muscle membrane; cross-bridge formation
2) Action potential in the muscle membrane; depolarization of the T tubules; release of Ca₂⁺ from the sarcoplasmic reticulum (SR)
3) Action potential in the muscle membrane; splitting of adenosine triphosphate (ATP); binding of Ca₂⁺ to troponin C
4) Release of Ca₂⁺ from the SR; depolarization of the T tubules; binding of Ca₂⁺ to troponin C

Answer 1

The correct sequence for excitation-contraction coupling is initiated by an action potential, followed by depolarization of the T tubules and the release of Ca2+ from the SR.

Step-by-step explanation:

The correct sequence for excitation-contraction coupling in skeletal muscle starts with the propagation of an action potential along the sarcolemma, moving down the T-tubules, which triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR). The calcium ions then bind to troponin, which is part of the thin filaments, initiating the movement of tropomyosin and exposing binding sites for myosin to form cross-bridges, leading to muscle fiber contraction. Therefore, the correct temporal sequence is option 2) Action potential in the muscle membrane; depolarization of the T tubules; release of Ca2+ from the SR.