Skeletal muscle is made of a number of muscle bundles or fascicles that our held together by a common collagenous connective tissue layer called fascia.
ii. Each muscle bundle contains a number of muscle fibres.
iii. Each muscle fibre is lined by the plasma membrane known as sarcolemma enclosing the sarcoplasm.
iv. Since the muscle fibre's sarcoplasm contains many nuclei it is caleed as a is a syncitium.
v. The sarcoplasmic reticulum of the muscle fibres is the store house of calcium ions.
vi. The muscle fibre has a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.
vii. Each myofibril has alternate dark and light bands on it. The striated appearance is due to the distribution pattern of Actin and Myosin proteins. The light bands contain actin and is called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin.
viii. In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line . The thin filaments are firmly attached to the ‘Z’ line. The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called ‘M’ line.
ix. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere.