Relaxation of Muscle Fibres

During relaxation, the events of contraction occur in reverse. Once nerve stimulation is terminated, the actomyosin complex is broken down and the myosin head detaches from the actin filament — a process that itself requires ATP. At the same time, calcium ions are actively pumped back into the sarcoplasmic reticulum, which is also an active, energy-requiring process. As calcium ions disappear from the sarcoplasm, the troponin-tropomyosin complex is restored and again covers the active sites on the actin filament. Because actin and myosin can no longer interact, the actin filaments slide back to their original position, and the muscle fibre relaxes. L …