MICROANATOMY

Detailed explanation-1: -In striated muscle, Ca2+ controls the position of tropomyosin on F-actin via the troponin complex. The troponin complex consists of three subunits: tropomyosin-binding (TnT), inhibitory (TnI), and Ca2+ sensor (TnC).

Detailed explanation-2: -The molecular regulation of striated muscle contraction couples the binding and dissociation of Ca2+ on troponin to the movement of tropomyosin on actin filaments.

Detailed explanation-3: -Muscle thin filament consists of actin, tropomyosin and troponin, and Ca2+ binding to troponin triggers conformational changes of troponin and tropomyosin to allow actin-myosin interactions.

Detailed explanation-4: -4.1. Visualization of troponin on actin filaments (F-actin). Troponin plays a central role in the calcium-regulation of muscle contraction: Troponin is the sole calcium-binding component of thin filaments (actin-tropomyosin-troponin complex) of striated muscles.

Detailed explanation-5: -Binding myosin shifts tropomyosin from the closed state (where myosin binds actin only weakly) to the open state (where myosin binds actin strongly) (4, 5).