Skeletal muscles are different from visceral muscles as these muscles show striations and are voluntary in nature. These are made up of many bundles known as Fasciculi. Each bundle has many muscle fibres which in turn has many myofibrils. Each myofibril consists of repeating units called as sarcomere. This is the main functional unit of contraction and relaxation of muscles. One sarcomere is the portion between two Z lines. Z lines bisect the 'I' or Isotrophic or light bands. In the centre of Sarcomere or between two Z lines there are present Dark bands or 'A'orAnisotrophic bands. Hensons zone or H zone is also seen in the centre which is demarcated by M line in the middle. Dark band has both actin and myosin fibres and hence appears dark. Hensons zone has only myosin filaments and hence appears paler.