troponin is a component of thin filaments (along with actin and tropomyosin), and is the protein complex to which calcium binds to trigger the production of muscular force. troponin itself has three subunits, tnc, tni, and tnt, each playing a role in force regulation . under resting intracellular levels of calcium, tropomyosin covers the active sites on actin to which myosin (a molecular motor organized in muscle thick filaments) binds in order to generate force. when calcium becomes bound to specific sites in the n-domain of tnc, a series of protein structural changes occurs such that tropomyosin is rolled away from myosin-binding sites on actin, allowing myosin to attach to the thin filament and produce force and shorten the sarcomere.