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The Muscular System

             Muscle tissue is one of the four basic tissue types that exist in the human body. There are three different muscle tissues: skeletal, cardiac, and smooth. They all have different organizations. Skeletal muscle tissue cells are long, cylindrical, striated, and have many nucleus. Cardiac muscle tissue, just like the skeletal is also in striations. However, these cells are short and branched. Unlike, the skeletal muscle tissue these cells die single nucliated. They are connected by intercolated discs. Smooth muscle tissue is not striated. Cells are short, spindle- shaped. Like the cardiac muscle it too is single nucleated. .
             The T tubules in a cardiac muscle cell are short and broad and no trads. The T tubules encircle the sarcomeres at the Z lines rather than at the zone of overlap. The SR of a cardiac muscle cell lacks terminal cisternae. The appearance of an action potential triggers calcium release from the SR and contraction of sarcomeres like in skeletal muscle. Cardiac muscle cells are almost totally dependent on aerobic metabolism to obtain the energy needed to continue contracting. Cardiac muscle cell contractions last roughly 10 times longer than do those of skeletal muscle fibers.
             Smooth muscle occurs within almost every organ, forming sheets, bundles, or sheat .
             around other tissues. Smooth muscle fiber has no T tubules and the SR forms a loose network throughout the sarcoplasm. It has no sarcomeres or myofibrils. The myosin proteins are organized differently than in cardiac and skeletal muscle. IN smooth muscle the collagen fibers never unite to form tendons as in skeletal muscles. Smooth muscle also differs with other muscle tissues in excitation, length-tension, control of contractions and smooth muscle tone.
             Cardiac and smooth muscle contractions are more affected by changes in extracellular Ca .
             2+ than skeletal muscle. Smooth muscles can contract over a wide range of resting lengths than skeletal muscle can.

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