Sliding Filament theory

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.