text: what is the cellular and molecular basis of muscle contraction,including the roles of actin, myosin, ca+2, atp   1. at the neuromuscular juncture, ach released by the synaptic terminal binds to receptors on the sarcolemma.  2. the resulting change in the transmembrane potential of the muscle fiber leads to the production of action petential that spreads across the entire surface of the muscle fiber and along the t tubules.  3.the sarcoplasmic reticulum releases stored calcium ions, increasing the calcium concentration of the sarcoplasm in and around the sarcomeres.  4. calcium ions bind to triponin, producing a change in the orientation of the troponin-tropomyosin complex that exposes active sites on the thin filaments (actin).  cross-bridges form when myosin heads bind to the active sites on f actin.  5. the contraction begins as repeated cycles of cross-bridge binding, pivoting, and detatchment occur, powered by the hydrolysis of atp.  these events produce filament sliding, and the muscle fiber shortens.