Skeletal Muscle

Skeletal muscle contraction involves many muscle proteins as well as sodium (Na⁺) and potassium (K⁺) and adenosine triphosphate (ATP), and vital ions such as magnesium (Mg²⁺) and calcium (Ca²⁺). The whole muscle contracts by way of individual sarcomere shortening. A sarcomere is Z-line to Z-line. After the ATP is broken down, the myosin head (thick filament head) cocks, and the release of Ca²⁺ from the sarcoplasmic reticulum upon electrical stimulation through the T-tubule system ensures that Ca²⁺ binds to troponin. Once the Ca²⁺ binds to troponin, tropomyosin moves away from the myosin head binding site on actin. The myosin head binds and muscle contraction ensues—myosin head moving actin. The ATP then binds to the myosin head again, is split and released from actin, Ca²⁺ is taken back up into the sarcoplasmic reticulum and relaxation ensues, or the process of shortening continues if Ca²⁺ is still in the local environment.