Sarcomere is the functional unit of myofibril. It is the part of myofibril between two successive Z-lines, which consists of two Iband halves, and an A-band between them. The region contains a bundle of two types of protein filaments, actin and myosin. Upon contraction, the actin filaments slide towards the centre of the myosin filaments,andoverall sarcomere length get smaller.