Animal tissues: Muscular tissues
The animal tissues have been classified into four different types that are epithelial tissue, connective tissue, muscular tissue, nervous tissue.
Muscular tissue arises from the embryonic mesoderm and the muscle cells are called myocytes. The cytoplasm of muscle fibre is called sarcoplasm. Sarcoplasm contains a network of sarcoplasmic reticulum or SR.
Muscles are made up of thin and elongated muscle fibres.
The three major types of muscles are striated muscles, unstriated muscles and cardiac muscles.
Striated muscle is found in the tongue, pharynx and in the beginning of oesophagus. These muscles are made up of several elongated, narrow, cylindrical and unbranched fibres with blunt end. “A” band is anisotropic, while “I” band is isotropic. “A” band gives a dark appearance under the microscope whereas I band gives a light appearance under the microscope. “A” band has a wide light zone at its middle known as Hensen’s line or H zone whereas I band has a dark membrane at its centre known as Z line or Z band or membrane of Krause.
The functional unit of myofibrils is called sarcomere which is made up of two types of myofilaments namely, thin actin myofilament and thick myosin myofilament.
Thin actin filaments are composed of three proteins namely actin, tropomyosin and troponin whereas thick myosin filaments are made up of two proteins namely myosin and meromyosin.
Single unit smooth muscle and multi unit smooth muscles are the two types of unstriated muscles.
Cardiac muscles are found in the wall of heart. They consist of fibres arranged in three dimensional network. These muscles are innervated both by the sympathetic and the parasympathetic nerves.
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