Muscle contraction occurs when an electrical impulse is sent from the neuromuscular junction. This impulse causes a depolarization of the muscle membrane. The sarcoplasmic reticulum then begins to release calcium ions which bind to troponin in the muscle. This subsequently causes the tropomyosin to slide along the actin filament causing the muscle to contract. (Squire, 2010)
Excitation-contraction coupling occurs in the plasma membrane and is the sequence of events that allows action