Sarcomere Contraction Cycle — a labelled NEET Biology diagram with a definitions lexicon.
Sarcomere Contraction Cycle Labelled parts: Sarcomere, Z-line, I-band, A-band, H-zone, Thick filament (myosin), Thin filament (actin), Tropomyosin, Troponin, Myosin head, Actin, ATP, ADP, Pi, Ca²⁺, Relaxed sarcomere, Contracted sarcomere, Cross-bridge cycle, Power stroke, ATP binding sites. It is the central region of the sarcomere where the actin filaments overlap with the myosin filaments, resulting in the maximum concentration of myosin heads. FYI: The H-zone is visible in resting muscle fibers and disappears during maximum contraction (sarcomere shortening). This filament is composed primarily of myosin molecules, which have globular heads that bind to actin and facilitate muscle contraction. FYI: Myosin heads bind to actin and hydrolyze ATP to generate the force required for the cross-bridge cycle. This filament is composed of polymerized actin subunits and is associated with regulatory proteins like tropomyosin and troponin. FYI: Troponin complex (TnI, TnT, TnC) controls the binding of myosin to actin by shifting tropomyosin. It is the cyclical process of attachment, power stroke, and detachment of myosin heads to actin filaments, which generates muscle force. FYI: The cycle is initiated by the binding of calcium ions (Ca²⁺) to troponin, allowing myosin to bind to actin. This is the conformational change in the myosin head that occurs after the hydrolysis of ATP, pulling the thin filament toward the center of the sarcomere. FYI: The power stroke is directly responsible for the shortening of the sarcomere and the contraction of the muscle fiber.