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Muscular tissue |
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Specialised cells whose primary function is contraction characterize muscular tissue. These cells, called muscle fibres, are elongated and arranged in parallel arrays. Their coordinated contraction results in movement.
Muscular tissue may be classified based on appearance and location. Striated muscle exhibits cross-striations visible under the microscope, while smooth muscle does not. Striated muscle may be further divided into skeletal muscle and cardiac muscle. Skeletal muscle is, for obvious reasons, under voluntary nervous control and is often referred to as voluntary muscle. Smooth muscle is under autonomic nervous control and is largely restricted to the viscera and blood vessels. |
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Cardiac muscle is a form of striated muscle, but differs from skeletal muscle in the following:
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Smooth muscle fibres are spindle-shaped with a single centrally located nucleus. The actin and myosin filaments are arranged in a meshwork throughout the cell except in the nuclear area, therefore smooth muscle cells do not display the striations characteristic of striated muscle.
The filaments are anchored to each other and to the cell membrane by dense bodies. These cells lack a T-tubule system and rely on extracellular calcium for contraction. |
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