MUSCLE PHYSIOLOGY

Detailed explanation-1: -When calcium floods the cell, troponin binds to it, moving tropomyosin off the myosin binding sites. Opening the myosin binding site on the actin filaments allows the myosin motors to crawl along the actin, resulting in a contraction of the muscle fiber.

Detailed explanation-2: -When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites. The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated; the calcium ions then enable the cross-bridge muscle contraction cycle.

Detailed explanation-3: -In these models, the Ca2+-induced change takes place in one troponin molecule can be transferred to one tropomyosin molecule, which in turn spreads the change to several actin molecules covered by one tropomyosin.

Detailed explanation-4: -Ca2+ binding to troponin initiates thin filament activation exposing myosin binding sites on actin. However, unlike in skeletal muscle, thin filament activation in cardiac muscle is not achieved primarily by Ca2+ binding alone (16, 17, 37).