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Motor mechanisms II Review questions Binding of ATP to myosin head causes: • a) actin filament to slide • b) Myosin head to detatch from actin filament • C) Myosin head to cock What will happen when ADP and Pi dissociate from myosin head? • A) head will detatch from actin filament • B) head will retract and pull actin filament • C) head will bind ADP again ++ Ca induces muscle contraction by: • A) Causing actin monomers to assemble into a filament • B) making ATP available to bind to myosin head • C) allowing myosin head to bind to actin filament Muscle fiber types are the result of different types (isoforms) of myosin • Type I - slow fibers (aerobic) • Type II - fast fibers (anaerobic) – Type IIx - very fast – Type IIa - intermediate between II x and I – Types present in other vertebrates, not humans e.g., IIb in rats and other small mammals TYPE I - SLOW TWITCH Tonic muscles (darker: red) - Leg muscles TYPE II - (IIa & IIx) FAST TWITCH Tetanic muscles (paler: white) - Pectoral muscles slower contraction times (100-110 msec) faster contraction times (50 msec) contain myoglobin (red) no myoglobin (white) continuous use muscles - prolonged performance for endurance performance ( marathoners) one time use muscles - brief performances for power & speed (sprinters) marathoner: 80% type I & 20% type II sprinter: 20% type I & 80% type II best in long slow sustained contractions best in rapid (short) contractions not easily fatigued easily fatigued more capillary beds, greater VO2 max less capillary beds smaller in size larger in size lower glycogen content higher glycogen content poor anaerobic glycolysis * predominantly anaerobic glycolysis easily converts glycogen to lactate w/o O2 * predominant aerobic enzymes & metabolism some aerobic capacity higher fat content lower fat content more mitochondria - Beta Oxidation high fewer mitochondria- Beta Oxidation low poorly formed sarcoplasmic reticulum well formed sacroplasmic reticulum slower release of Ca = slower contractions quick release of Ca = rapid contractions tropinin has lower affinity for Ca troponin - higher affinity for Ca Changes between fiber types • In response to weigh training and anaerobic exercise – IIx ---> IIa – I --> Iia • Can IIa --> I? • Can increase cross sectional area of fast fiber types by weigh training Weight Training and Different Myosin Types sedentary people have higher amounts of IIx active people have more IIa fibers heavy weight-load repetitions..... decreases Fast IIx fibers and converts them to Fast IIa fibers nuclei stop expressing IIx gene and express IIa genes after 1 month all IIx --> IIa (muscle also become more massive) Can we recruit slow ---> fast ? maybe... but no good evidence to date for slow to fast recruitments. Characteristics of other muscle types: • Cardiac muscle - found only in the heart, striated, gap junctions allow direct electrical signaling between cells • Smooth muscle - involuntary muscle, meshwork of actin and myosin, can contract more (greater shortening), but with less tension. 1 2 3 Muscle cell types schematic: 1) skeletal 2) cardiac 3) smooth Skeletal muscle Cardiac muscle http://www.youtube .com/watch?v=Cdl8 Awn_lDY&feature= related http://www.youtube .com/watch?v=b1W D564sjWw&feature =related Smooth muscle