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Lecture 3

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BIOL 103
Virginia K Walker

WEEK 3 MUSCLES AND NEURONSMUSCLE STRUCTUREthin filament actin troponin tropomyosinthick filament myosincytosol of muscle fibres filled with myofibrils made of thick and thin filamentssarcomere one repeating unit of thinthick filamentsthick filament in middle of sarcomere wide dark Ababdthin filaments beside thick anchored by proteinsZlines bw Zlines is the limit of asarcomerecrossbridges spaces bw overlapping thick and thin filaments are bridged by these projections regions of myosin molecules that extend from the thick to thin filaments during muscle contraction crossbridges activated sarcomeres shorten but no changeinlengththick filament is stationary while thin filament slides to shorten during sliding each myosin crossbridge attached to a thin filament actin molecules also called myosin heads 3 MAJOR TYPES OF MUSCLE FIBRESdifferent muscle fibres have diff forms of myosin that differ in max rate of ATP hydrolysisdetermines max rate of crossbridge cycling and muscle shortneingOxidative Fibresnumerous mitochondria high capacity for oxidative phosphorylationmost of the ATP production depends on blood flow to deliver O2 and nutrients to muscle these fibres surrounded by many small blood vesselscontains lots of myoglobin which increases availability of O2 in the fibre by providing an intracellular reservoir of O2lots of myoglobindark red colourGlycolytic Fibresfew mitochondria high glycolytic enzymes and lots of glycogenlimited use of O2fibres surrounded by few blood vessels and have little myoglobinlack of myoglobinpale colour FASTOXIDATIVE FIBREShigh myosin ATPase activity can make lots of ATPfibres dont fatigue quickly used for longterm activityfor rapid actions and movement eg vocal cord muscles in trilling birds rattlesnakes tailSLOWOXIDATIVE FIBRESlow myosin ATPase activity can make lots of ATPused for prolonged regular activity flight longdistance swimming maintenance of posturewalkingthese types of activities that require muscles that do not fatigue quicklygives red colour to meat eg breast meat of ducks for flight is redFASTGLYCOLYTIC FIBREShigh myosin ATPase activity little ATP made bc source of ATP is glycolysisfor rapid intense actions short sprints at max speed pouncing on preyfatigue more rapidly than oxidative fibres white colour due to lack of myoglobin eg breast meat of nonflying chickens
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