GENERAL HISTOLOGY

Detailed explanation-1: -Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation, which prevents contraction in a muscle without nervous input. The protein complex troponin binds to tropomyosin, helping to position it on the actin molecule.

Detailed explanation-2: -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).

Detailed explanation-3: -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-4: -In vertebrate striated muscle, troponin and tropomyosin on actin filaments comprise a Ca(2+)-sensitive switch that controls contraction. Ca(2+ )binds to troponin and triggers a series of changes in actin-containing filaments that lead to cyclic interactions with myosin that generate contraction.