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| Yves Clermont, Michael Lalli, Zsuzsanna Bencsath-Makkai |
LIGHT-MICROSCOPIC HISTOLOGY ATLAS
Version française
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3. Muscle Tissue |
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| | The cytoplasm of most cells has the capacity to contract, but contractility is the main function of muscle cells. There are structurally two main classes of muscle cells or fibres: striated muscle fibres and smooth muscle fibres. Striated muscle cells are characterized by cytoplasmic subunits, the myofibrils, which show visible cross striations. There are two classes of striated fibres: skeletal muscle fibres (Figure 3.1A ) and cardiac muscle fibres (Figure 3.1B). Skeletal muscle fibres respond to voluntary nervous stimuli. Some of these cells are attached to bones and cartilages by means of tendons and play a role in locomotion, while others are inserted in dense connective tissue fibres such as those of the face, tongue, pharynx, and larynx. Cardiac muscle fibres, under the influence of the autonomic nervous system, control involuntary rhythmic contractions that spread from the atria to the ventricles of the heart. Smooth muscle fibres (Figure 3.1C) are characterized by their fusiform or stellate shape. Their contractions are involuntary and stimulated by the autonomic nervous system. Their cytoplasm contains an abundance of contractile filaments which are not organized as cross-striated myofibrils. Bundles of smooth muscle fibres are widely distributed throughout the body. Present in the wall of blood vessels, they are abundant along the gastro-intestinal tract. In the intestine they are responsible for peristaltic contractions. Smooth muscle fibres are also components of the respiratory passages and of the ducts in the urinary system and the male and female reproductive systems. There are other varieties of contractile cells, such as the myoepithelial cells associated with glands. |
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HAweb/Zs B-M -> HAbase-generated on 2013-09-13
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