The reasoning: mechanical coupling in skeletal muscle
Thick filaments: myosin II (two heavy chains with ATPase heads, four light chains). Thin filaments: F‑actin, tropomyosin, troponin (TnC binds Ca²⁺, TnI inhibits, TnT binds tropomyosin). Titin anchors thick filaments to Z discs (passive elasticity); nebulin rules thin‑filament length; dystrophin links the cytoskeleton to the sarcolemmal glycoprotein complex and matrix. In mammalian skeletal muscle, triads (T tubule + two SR terminal cisternae) lie at the A–I junction.