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Muscle
Bundle of muscle fibers.
Muscle fiber
Consists of myofibrils.
Myofibrils
Composed of myofilaments (actin + myosin).
Actin
Thin myofilament.
Myosin
Thick myofilament.
Sarcomere
Functional unit of myofibril, separated by Z-lines.
I band
Distance between myosin strands.
A band
Length of myosin.
H zone
Distance between actin strands.
Z line
End of the sarcomere.
Sarcoplasmic reticulum
Stores calcium ions.
Troponin
Binds calcium ions, allowing contraction to begin.
ATP
Hydrolyzed to energize myosin heads for the power stroke.
Power stroke
Myosin attaches to actin, pulls filaments, and releases energy.
Ratchet motion
Movement of myosin head during contraction.
Contraction cycle
Continues with ATP and calcium availability.
