Define muscular tissue. Classify and explain different types of muscles with the help of suitable diagrams.
Contractile tissue is made up of muscle cells or muscle fibres. The muscle cells bring about the movements of body or limbs by contraction and relaxation of contractile proteins located in the muscle cells.
On the basis of location, structure, and function of muscle cells, muscle tissue is classified into following three types :
1. Striated muscles :
These are also referred to as voluntary muscles, because they work according to our will. The striated muscle fibres are elongated, non-tapering, cylindrical, and unbranched, and each fibre is enclosed in a thin plasma membrane called sarcolemma. These are located in the muscle of the limbs, body wall, face, neck, etc. Striated muscles provide the force for locomotion and all other voluntary movements of the body.
2. Smooth muscles :
They are also referred to as involuntary muscles, as they do not work according to our will. The smooth muscle cells are spindle-shaped and held together via loose connective tissue. Myofibrils are contractile threads that run longitudinally throughout the cell. They are located in the walls of hollow visceral organs (except heart) such as walls of alimentary canal, ducts of glands, urogenital ducts, and blood vessels. The peristaltic movements of gastrointestinal tract are brought about by smooth muscle cells.
3. Cardiac muscles:
They consist of branched fibres that join to form a network. Each cells consist of myofibrils and sarcolemma. They are located in the walls of the heart. The contraction and relaxation of these muscles help the heart to pump blood and distribute it to different parts of the body.
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