BackMuscle Contractions definitions
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1/15BackSkip to main contentBackActin
A thin filament protein in muscle fibers that interacts with myosin to enable contraction by sliding past thick filaments. Myosin
A thick filament protein with two ATPase heads and a coiled tail, responsible for binding and moving actin during contraction. Sarcomere
The smallest contractile unit within myofibrils, defined by Z lines, where actin and myosin interact for muscle contraction. Myofibril
A bundle of actin and myosin filaments within muscle fibers, composed of repeating sarcomeres, essential for contraction. A Band
A dark region in the sarcomere containing the full length of myosin filaments, including areas overlapping with actin. I Band
A light region in the sarcomere containing only actin filaments, with no overlap of myosin. H Zone
A lighter region within the A band where myosin filaments are present without overlapping actin. Z Line
The boundary structure at each end of a sarcomere, anchoring actin filaments and moving closer during contraction. M Line
A central disc in the sarcomere's middle, stabilizing the arrangement of myosin filaments. Tropomyosin
A regulatory protein that blocks actin binding sites in relaxed muscle, preventing myosin attachment until shifted. Troponin
A protein complex on actin filaments that binds calcium, triggering tropomyosin movement to expose binding sites. Cross Bridge
A structure formed when myosin heads attach to actin, enabling filament overlap and sarcomere shortening. ATP Hydrolysis
A chemical reaction providing energy for myosin conformational change, allowing tight actin binding during contraction. Calcium
An ion that binds to troponin, initiating the exposure of actin binding sites for myosin attachment. Relaxed State
A muscle condition where actin and myosin filaments have minimal overlap, and the sarcomere is at maximum length.
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