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Structure and Function of Skeletal MuscleSkeletal MusclenHuman body contains over 400 skeletal musclesn40-50%of total body weightnFunctions of skeletal musclenForce production for locomotion and breathingnForce production for postural supportnHeat production during cold stressStructure of Skeletal Muscle:Connective Tissue CoveringnEpimysiumnSurrounds entire musclenPerimysiumnSurrounds bundles of muscle fibersnFasciclesnEndomysiumnSurrounds individual muscle fibersStructure of Skeletal Muscle:MicrostructurenSarcolemmanMuscle cell membranenMyofibrilsnThreadlike strands within muscle fibersnActin(thin filament)nTroponinnTropomyosinnMyosin(thick filament)Structure of Skeletal Muscle:The SarcomerenFurther divisions of myofibrilsnZ-linenA-bandnI-bandnWithin the sarcoplasmnSarcoplasmic reticulumnStorage sites for calciumnTransverse tubulesnTerminal cisternaeThe Neuromuscular JunctionnSite where motor neuron meets the muscle fibernSeparated by gap called the neuromuscular cleftnMotor end platenPocket formed around motor neuron by sarcolemmanAcetylcholine is released from the motor neuronnCauses an end-plate potential(EPP)nDepolarization of muscle fiberIllustration of the Neuromuscular JunctionMotor UnitnSingle motorneuron&muscle fibers it innervatesnEye muscles 1:1 muscle/nerve rationHamstrings 300:1 muscle/nerve ratioMuscular ContractionnThe sliding filament modelnMuscle shortening occurs due to the movement of the actin filament over the myosin filamentnFormation of cross-bridges between actin and myosin filamentsnReduction in the distance between Z-lines of the sarcomereThe Sliding Filament Model of Muscle ContractionCross-Bridge Formation in Muscle ContractionSliding Filament TheorynRest uncharged ATP cross-bridge complexnExcitation-coupling charged ATP cross-bridge complex,“turned on”nContraction actomyosin ATP ADP&Pi+energynRecharging reload cross-bridge with ATPnRelaxation cross-bridges“turned off”Muscle FunctionnAll or none law fiber contracts completely or not at allnMuscle strength gradation nMultiple motor unit summation more motor units per unit of timenWave summation vary frequency of contraction of individual motor unitsEnergy for Muscle ContractionnATP is required for muscle contractionnMyosin ATPase breaks down ATP as fiber contractsnSources of ATPnPhosphocreatine(PC)nGlycolysisnOxidative phosphorylationSources of ATP for Muscle ContractionProperties of Muscle FibersnBiochemical propertiesnOxidative capacitynType of ATPasenContractile propertiesnMaximal force productionnSpeed of contractionnMuscle fiber efficiencyIndividual Fiber TypesFast fibersnType IIb fibers nFast-twitch fibersnFast-glycolytic fibersnType IIa fibersnIntermediate fibersnFast-oxidative glycolytic fibersSlow fibersnType I fibersnSlow-twitch fibersnSlow-oxidative fibersComparison of Maximal Shortening Velocities Between Fiber TypesHistochemical Staining of Fiber TypeFiber Types and PerformancenPower athletes nSprintersnPossess high percentage of fast fibersnEndurance athletes nDistance runnersnHave high percentage of slow fibersnOthersnWeight lifters and nonathletesnHave about 50%slow and 50%fast fibersAlteration of Fiber Type by TrainingnEndurance and resistance trainingnCannot change fast fibers to slow fibersnCan result in shift from Type IIb to IIa fibersnToward more oxidative propertiesTraining-Induced Changes in Muscle Fiber TypeHypertrophy and HyperplasianIncrease in sizenIncrease in numberAge-Related Changes in Skeletal MusclenAging is associated with a loss of muscle massnRate increases after 50 years of agenRegular exercise training can improve strength and endurancenCannot completely eliminate the age-related loss in muscle massTypes of Muscle ContractionnIsometricnMuscle exerts force without changing lengthnPulling against immovable objectnPostural musclesnIsotonic(dynamic)nConcentricnMuscle shortens during force productionnEccentricnMuscle produces force but length increasesIsotonic and Isometric ContractionsIllustration of a Simple TwitchForce Regulation in MusclenTypes and number of motor units recruitednMore motor units=greater forcenFast motor units=greater forcenInitial muscle lengthn“Ideal”length for force generationnNature of the motor units neural stimulationnFrequency of stimulationnSimple twitch,summation,and tetanusRelationship Between Stimulus Frequency and Force GenerationLength-Tension Relationship in Skeletal MuscleSimple Twitch,Summation,and TetanusForce-Velocity RelationshipnAt any absolute force the speed of movement is greater in muscle with higher percent of fast-twitch fibersnThe maximum velocity of shortening is greatest at the lowest forcenTrue for both slow and fast-twitch fibersForce-Velocity RelationshipForce-Power RelationshipnAt any given velocity of movement the power generated is greater in a muscle with a higher percent of fast-twitch fibersnThe peak power increases with velocity up to movement speed of 200-300 degreessecond-1nForce decreases with increasing movement speed beyond this velocityForce-Power RelationshipReceptors in MusclenMuscle spindlenDetect dynamic and static changes in muscle lengthnStretch reflexnStretch on muscle causes reflex contractionnGolgi tendon organ(GTO)nMonitor tension developed in musclenPrevents damage during excessive force generationnStimulation results in reflex relaxation of muscleMuscle SpindleGolgi Tendon OrganThis powerpoint was kindly donated to http:/ is home to over a thousand powerpoints submitted by teachers.This is a completely free site and requires no registration.Please visit and I hope it will help in your teaching.
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