As a result of effective neuromuscular transmission, action potential is produced in the muscle cell membrane, which eventually leads to contraction of the cell through a series of processes called excitation-contraction(E-C) coupling. As is well known, it is calcium ion that plays the central role in the E-C coupling. Action potential is conducted deep into the muscle cell through the T-tubule system. In the tubular membrane action potential (depolarization) is detected by voltage sensor molecules, which in turn send a signal to calcium release channels in the neighboring organella, sarcoplasmic reticulum (SR). Calcium ion released from SR binds to C subunit of troponin molecules on the thin filament in myofibrils, and resulting conformational change of the troponin removes the repression that had been exerted in the absence of calcium ion on actin molecules in the thin filament through tropomyosin molecules to finally cause myosin-actin interaction, i.e., contraction.