骨骼肌的结构和功能

StructureandFunctionofSkeletalMuscleSkeletalMuscleHumanbodycontainsover400skeletalmuscles40-50%oftotalbodyweightFunctionsofskeletalmuscleForceproductionforlocomotionandbreathingForceproductionforposturalsupportHeatproductionduringcoldstressStructureofSkeletalMuscle:

ConnectiveTissueCoveringEpimysiumSurroundsentiremusclePerimysiumSurroundsbundlesofmusclefibersFasciclesEndomysiumSurroundsindividualmusclefibersStructureofSkeletalMuscle:

MicrostructureSarcolemmaMusclecellmembraneMyofibrilsThreadlikestrandswithinmusclefibersActin(thinfilament)TroponinTropomyosinMyosin(thickfilament)StructureofSkeletalMuscle:

TheSarcomereFurtherdivisionsofmyofibrilsZ-lineA-bandI-bandWithinthesarcoplasmSarcoplasmicreticulumStoragesitesforcalciumTransversetubulesTerminalcisternaeTheNeuromuscularJunctionSitewheremotorneuronmeetsthemusclefiberSeparatedbygapcalledtheneuromuscularcleftMotorendplatePocketformedaroundmotorneuronbysarcolemmaAcetylcholineisreleasedfromthemotorneuronCausesanend-platepotential(EPP)DepolarizationofmusclefiberIllustrationoftheNeuromuscularJunctionMotorUnitSinglemotorneuron&musclefibersitinnervatesEyemuscles–1:1muscle/nerveratioHamstrings–300:1muscle/nerveratioMuscularContractionTheslidingfilamentmodelMuscleshorteningoccursduetothemovementoftheactinfilamentoverthemyosinfilamentFormationofcross-bridgesbetweenactinandmyosinfilamentsReductioninthedistancebetweenZ-linesofthesarcomereTheSlidingFilamentModelofMuscleContractionCross-BridgeFormationinMuscleContractionSlidingFilamentTheoryRest–unchargedATPcross-bridgecomplexExcitation-coupling–chargedATPcross-bridgecomplex,“turnedon”Contraction–actomyosin–ATP>ADP&Pi+energyRecharging–reloadcross-bridgewithATPRelaxation–cross-bridges“turnedoff”MuscleFunctionAllornonelaw–fibercontractscompletelyornotatallMusclestrengthgradationMultiplemotorunitsummation–moremotorunitsperunitoftimeWavesummation–varyfrequencyofcontractionofindividualmotorunitsEnergyforMuscleContractionATPisrequiredformusclecontractionMyosinATPasebreaksdownATPasfibercontractsSourcesofATPPhosphocreatine(PC)GlycolysisOxidativephosphorylationSourcesofATPforMuscleContractionPropertiesofMuscleFibersBiochemicalpropertiesOxidativecapacityTypeofATPaseContractilepropertiesMaximalforceproductionSpeedofcontractionMusclefiberefficiencyIndividualFiberTypesFastfibersTypeIIbfibersFast-twitchfibersFast-glycolyticfibersTypeIIafibersIntermediatefibersFast-oxidativeglycolyticfibersSlowfibersTypeIfibersSlow-twitchfibersSlow-oxidativefibersComparisonofMaximalShorteningVelocitiesBetweenFiberTypesHistochemicalStainingofFiberTypeFiberTypesandPerformancePowerathletesSprintersPossesshighpercentageoffastfibersEnduranceathletesDistancerunnersHavehighpercentageofslowfibersOthersWeightliftersandnonathletesHaveabout50%slowand50%fastfibersAlterationofFiberTypebyTrainingEnduranceandresistancetrainingCannotchangefastfiberstoslowfibersCanresultinshiftfromTypeIIbtoIIafibersTowardmoreoxidativepropertiesTraining-InducedChangesinMuscleFiberTypeHypertrophyandHyperplasiaIncreaseinsizeIncreaseinnumberAge-RelatedChangesinSkeletalMuscleAgingisassociatedwithalossofmusclemassRateincreasesafter50yearsofageRegularexercisetrainingcanimprovestrengthandenduranceCannotcompletelyeliminatetheage-relatedlossinmusclemassTypesofMuscleContractionIsometricMuscleexertsforcewithoutchanginglengthPullingagainstimmovableobjectPosturalmusclesIsotonic(dynamic)ConcentricMuscleshortensduringforceproductionEccentricMuscleproducesforcebutlengthincreasesIsotonicandIsometricContractionsIllustrationofaSimpleTwitchForceRegulationinMuscleTypesandnumberofmotorunitsrecruitedMoremotorunits=greaterforceFastmotorunits=greaterforceInitialmusclelength“Ideal”lengthforforcegenerationNatureofthemotorunitsneuralstimulationFrequencyofstimulationSimpletwitch,summation,andtetanusRelationshipBetweenStimulusFrequencyandForceGenerationLength-TensionRelationshipinSkeletalMuscleSimpleTwitch,Summation,andTetanusForce-VelocityRelationshipAtanyabsoluteforcethespeedofmovementisgreaterinmusclewithhigherpercentoffast-twitchfibersThemaximumvelocityofshorteningisgreatestatthelowestforceTrueforbothslowandfast-twitchfibersForce-VelocityRelationshipForce-PowerRelationshipAtanygivenvelocityofmovementthepowergeneratedisgreaterinamusclewithahigherpercentoffast-twitchfibersThepeakpowerincreaseswithvelocityuptomovementspeedof200-300degrees•second-1ForcedecreaseswithincreasingmovementspeedbeyondthisvelocityForce-PowerRelationshipReceptorsinMuscleMusclespindleDetectdynamicandstaticchangesinmusclelengthStretchreflexStretchonmusclecausesreflexcontractionGolgitendonorgan(GTO)MonitortensiondevelopedinmusclePreventsdamageduringexcessiveforcegenerationStimulationresults