The Role of Calcium in Contraction

Release of calcium ions by the sarcoplasmic reticulum (Figure 8.15) in reponse to signals from the nervous system is the signal that ultimately stimulates muscular contraction. In the absence of calcium from the sarcoplasmic reticulum, access of the headpiece to the thin filament is blocked by the proteins tropomyosin and the troponins (I, C, and T) (Figure 8.13). Calcium binding by troponin C causes a rearrangement of the troponin-tropomyosin-actin complex, allowing actin-myosin cross-bridges to form.

See also: Actin and Myosin, The Structure of Muscle, The Sliding Filament Model, Tropomyosin, Troponins