MEDICAL PHYSIOLOGY

Detailed explanation-1: -As a result, the carboxyl-terminal region of tropomyosin shifts and covers the myosin-binding sites of actin to block the binding of myosin. At higher calcium concentrations, the troponin arm changes its partner from actin to the main body of calcium-loaded troponin.

Detailed explanation-2: -In each contracting unit or sarcomere, thin actin and thick myosin filaments are juxtaposed, but cannot interact in the absence of calcium. This is because myosin binding sites on the actin filaments are all covered by a rod-shaped protein called tropomyosin.

Detailed explanation-3: -Tropomyosin is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin.

Detailed explanation-4: -Without the presence of calcium, the myosin binding sites on the actin filaments are blocked by tropomyosin and muscle contraction cannot occur.

Detailed explanation-5: -Tropomyosin covers the actin binding sites, preventing myosin from forming cross-bridges while in a resting state. When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites.