Muscle Contraction: Regulation

Remarkably we can tell our arms or legs to move and they do it. We can directly control or regulate the activity of our skeletal muscles. Striated muscle movement, produced by the interaction of filaments containing the proteins myosin and actin, is regulated by the proteins tropomyosin and troponin on the actin filaments. When an electrical signal passes down the motor nerve to a muscle it triggers a depolarisation of the muscle membrane (sarcolemma). In turn this triggers the sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction. During relaxation calcium is pumped back into the sarcoplasmic reticulum, troponin loses its calcium and tropomyosin reverts to its off position. This is the steric blocking mechanism of muscle regulation.