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Muscle 2009 - 1 Muscle 2009 Before reading these notes I...

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1 Muscle 2009 Before reading these notes, I urge you to go to one or more of these websites and spend a little time. Some sites that should help you understand muscle structure and muscular function which is contraction: http://entochem.tamu.edu/MuscleStrucContractswf/index.html http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animati ons/muscles/muscles.html http://www.sci.sdsu.edu/movies/actin_myosin_gif.html http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html (or type sarcomere on your browser, then click on this site) http://www.blackwellpublishing.com/matthews/animate.html Muscle is one of the four basic tissues. While it is true most cells contain some actin and myosin, muscle cells contain a large amount of actin and myosin that is highly organized and precisely controlled. It is the interaction of these proteins that bring about contraction. For historical reasons, a few organelles in muscle cells have been called by special names. Smooth endoplasmic reticulum is called sarcoplasmic reticulum; the cell membrane is referred to as sarcolemma; and the cytoplasm of a muscle cell is called sarcoplasm . ( Sarkos is Greek for flesh; lemma is Greek for skin). There are three types of muscle. Each is specialized for movement through cellular contraction. I. Skeletal muscle is also called voluntary muscle. For the most part, it is connected to bone (exceptions being the tongue and diaphragm and couple other areas). It is composed of muscle fibers which are long
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2 cylindrical multinucleated cells which resulted from the fusion of embryonic myoblasts (myo =muscle). These cylindrical fibers are very long (up to 30cm-ie., one fiber, one cell can run the entire length of biceps or triceps) but the diameter of the cylinder stays fairly constant. There may be hundreds, even thousands, of nuclei in one muscle fiber (or skeletal muscle cell). These nuclei lie at the periphery of the cell adjacent to the cell membrane (sarcolemma), pushed to this peripheral position by the myofibrils of actin and myosin. This peripheral location of nuclei is in contrast to the position of nucleus in cardiac and smooth muscle tissues where the single nucleus (there maybe some exceptions to this in cardiac muscle) is in the center of the cell. Most of the sarcoplasm (cytoplasm) is occupied by myofibrils which are arranged longitudinally in a precise order. These myofibrils run the entire length of the muscle fiber (cell). The two main myofibrils are the actin and myosin, the major contractile proteins. But there are also accessory proteins which are vital for contraction: tropomyosin and troponin. Tropomyosin is wrapped around actin filaments. Troponin is attached to tropomyosin. These proteins, like all proteins, exist in a three dimensional configuration. Myosin has a globular head and a long tail. ( In addition to these proteins, the sarcoplasm contains many glycogen granules and mitochondria: contraction is work and it requires a lot of energy). It is the
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