ANATOMY

Detailed explanation-1: -(2) Calcium binds to troponin C, which induces a conformational change in the troponin complex. This causes tropomyosin to move deeper into the actin groove, revealing the myosin-binding sites.

Detailed explanation-2: -Troponin and tropomyosin are indispensable for the physiological regulation of striated muscle contraction. The reason why troponin is essential is straightforward to understand, because it binds calcium ions19) and changes its structure with Ca2+.

Detailed explanation-3: -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-4: -Each heartbeat is triggered by a pulse of intracellular calcium ions which bind to troponin on the actin-containing thin filaments of heart muscle cells, initiating a change in filament structure that allows myosin to bind and generate force.

Detailed explanation-5: -Upon binding calcium, troponin moves tropomyosin away from the myosin-binding sites on actin (bottom), effectively unblocking it.