InterviewSolution
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InterviewSolution
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Question : Discuss the microscopic structure of skeletal muscle tissue. |
Answer» Solution :Each organised skeletal muscle in our body is made of number of muscles bundles or fascircles HELD together by a common COLLAGENOUS connective tissue layer called fascia. Each muscle bundle contains a number of muscle fibres.  Diagrammatic cross sectional view of a muscle showing muscle bundles and muscle fibres Each muscle fibre is a lined by the plasma membrance called sarcollema enclosing sarcoplasm. Muscle fibres is syncitium as the sarcoplasm contains many nuclei. The endoplasmic reticulum of the muscle fibres (sarcoplasmic reticulum) is the store house of calcium ions. A characteristics feature of the muscle fibre is the PRESENCE of a large number of PARALLELLY arranged filaments in the sarcoplasm calle myofilaments or myofibrils. Each myofibril has alternate dark and light bands on it. It is due to the distribution pattern of the two important proteins - Actin and Myosin. The light bands contain actin is called I-band (Isotropic band). dark band called .A. (Anisotropic band contains myosin protein). Both the proteins are arranged as rod-like structures, parallel to each other and to the longitudinal axis of the myofibrils. Actin filaments are thinner as compared to the myosin filaments. In the centre of each .I. band is an elastic fibre called .Z. LINE which bisects it. The thin filaments are firmly attached tothe .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. 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. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments leaving the central part of the thick filaments. This central part of thick filament, not overlapped by thin filaments is called .H. zone. 
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