1. an action potential induced by the pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes, is conducted to contractile cardiomyocytes through gap junctions.
2. As the action potential travels between sarcomeres it activates the calcium channels in the T-tubules resulting in an influx of calcium ions into the cardiomyocyte.
3. calcium in the cytoplasm then binds to cardiac troponin-c which moves the troponin complex away from the actin binding site. This removal of the troponin complex frees the actin to be bound by myosin and initiates contraction.
4 the myosin head binds to ATP and pulls the actin filanents toward the center of the sarcomere contracting the muscle.
5.intracellular calcium is then removed by the sarcoplasmic reticulum dropping intracellular calcium concentration, returning the troponin complex to its inhibiting position on the active site of actin, and effectively ending contraction as the actin filaments return to their initial position relaxing the muscle.