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Muscle and the Sliding filament theory. Myoblasts one nucleus each lacking myofibrils. Myotubes develop myofibrils Many nuclei. FUSE. Skeletal muscle development. Skeletal and Cardiac Muscle. Both demonstrate “striations” or stripes when seen with a microscope
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Myoblasts one nucleus each lacking myofibrils Myotubes develop myofibrils Many nuclei FUSE Skeletal muscle development
Skeletal and Cardiac Muscle • Both demonstrate “striations” or stripes when seen with a microscope • These stripes represent the regular arrangement of actin and myosin
Myosin is a thick protein and looks dark in the section • Actin is a very small protein and looks pale in the section. The dark ovals are the nuclei of the muscle cells. There may be up to A 100 nuclei per cell
Sarcomeres • Functional contractile unit of striated muscle • 2-3 mm in length • Striations • Made up of regular overlapping pattern • of actin (thin filaments) • myosin (thick filaments) • Delineated by Z lines • Center line is I band
Very close image of muscle A band: myosin I band: actin Z lines: where the actin attaches and the end of a sarcomere
Muscle contraction • When muscle contracts, • all of the actin • (white in the picture, red in the diagram) • will slide over • the myosin • (black in the picture, green in the diagram). • The Z discs will come closer • All of these millions of shortenings in one muslce will result in muscle contractions
Sliding filament mechanism • Sarcomeres shortened • Thin filaments slide over thick filament • Requires ATP • The cells source of energy • other proteins and calcium
Animation of sliding filament • http://3dotstudio.com/zz.html