Question

detachment of myosin cross-bridges occurs during the

isotonic period.
contraction phase.
relaxation phase.
latent period.
stimulus phase.

Explanation:

🆕 New Concept Discovered: Muscle Twitch Phases
Understanding the physiological stages of a muscle contraction.

Step 1: Understand the phases of a muscle twitch

A muscle twitch is a single, rapid contraction and relaxation cycle of a muscle fiber in response to a single stimulus. It consists of three main phases:

1. Latent period: The delay between the stimulus and the start of tension generation. During this time, the action potential propagates and calcium ions are released from the sarcoplasmic reticulum.
2. Contraction phase: Calcium binds to troponin, active sites on actin are exposed, cross-bridges form, and the muscle shortens or develops tension.
3. Relaxation phase: Calcium ions are actively pumped back into the sarcoplasmic reticulum, troponin returns to its original shape, and myosin cross-bridges detach from actin, causing muscle tension to decrease.

Step 2: Identify when cross-bridge detachment occurs

During the relaxation phase, the active transport of calcium back into the sarcoplasmic reticulum leads to a decrease in sarcoplasmic calcium concentration. Without calcium bound to troponin, tropomyosin moves back to cover the active binding sites on actin. This prevents new cross-bridges from forming and leads to the detachment of existing myosin cross-bridges, allowing the muscle to return to its resting length.

Answer:

relaxation phase.