Question

In an initial latent period, an action potential generated in the muscle fiber triggers the release of calcium ions from the SR. In the contraction phase, calcium ions bind troponin and tension begins to increase. In the relaxation phase, tension decreases because cross-bridges have detached and because calcium ion levels have fallen; the active sites are once again covered by the troponin-tropomyosin complex. What happens in the initial latent period of muscle contraction?

1) The release of calcium ions from the SR is triggered
2) Tension begins to increase
3) Cross-bridges detach
4) Calcium ion levels fall

Answer 1

In the initial latent period of muscle contraction, the action potential triggers the release of calcium ions from the sarcoplasmic reticulum. These calcium ions then bind to troponin, leading to the exposure of actin-binding sites and preparing the muscle fiber for contraction.

Step-by-step explanation:

In the initial latent period of muscle contraction, the action potential generated in the muscle fiber triggers the release of calcium ions from the sarcoplasmic reticulum (SR). This is the phase during which the excitation and contraction are being coupled, but contraction has yet to occur. The released calcium ions then bind to troponin, resulting in a conformational change in the sarcomere and exposing the actin-binding sites. This prepares the muscle fiber for contraction.