Muscle and the Sliding filament theory

Skeletal muscle development Myoblasts one nucleus each lacking myofibrils Myotubes develop myofibrils Many nuclei FUSE

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, The Z discs will come closer 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 http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html