解剖学――肌肉_Muscular

TheMuscularSystem,INTRODUCTION,MusculartissueenablesthebodyanditspartstomoveThreetypesofmuscletissueexistinbody:SkeletalCardiacSmoothMovementcausedbymusclecells(calledfibers):shorteningorcontractingMusclemovementoccurswhenchemicalenergy(obtainedfromfood)isconvertedintomechanicalenergy,MUSCLETISSUE,TypesofmuscletissueSkeletalmusclealsocalledstriatedorvoluntarymuscleMicroscoperevealscrosswisestripesorstriationsContractionscanbevoluntarilycontrolledCardiacmusclecomposesbulkofheartCardiacmusclefibersarebranchedHasdarkbandscalledintercalateddisksIntercalateddiscssupportsynchronisedcontractionofcardiactissueCardiacmusclefiberinterconnectionsallowhearttocontractefficientlyasaunit,MUSCLETISSUE(cont.),Typesofmuscletissue(cont.)Nonstriatedmuscle,orinvoluntarymusclealsocalledsmoothorvisceralmuscleLackscrossstripesorstriationswhenseenunderamicroscope;appearssmoothFoundinwallsofhollowstructures,suchasdigestivetract,bloodvessels,etc.ContractionsnotundervoluntarycontrolFunctionallmusclefibersspecializeincontraction(shortening),STRUCTUREOFSKELETALMUSCLE,MuscleorgansmainlystriatedmusclefibersandconnectivetissueConnectivetissueforms“wrappers”aroundeachmusclefiber,aroundfascicles一簇(groups)ofmusclefibers,andaroundtheentiremuscleFascia筋膜surroundsmuscleorgansandnearbystructuresMostskeletalmusclesextendfromoneboneacrossajointtoanotherbone,STRUCTUREOFSKELETALMUSCLE(cont.),Muscleorgans(cont.)Musclesattachtobonebytendonsstrongcordsorsheetsoffibrousconnectivetissuethatextendfromthemuscleorgan;sometendonsenclosedinsynovial-linedtubes(tendonsheaths)andarelubricatedbysynovialfluidBursaesmallsynovial-linedsacscontainingasmallamountofsynovialfluid;locatedbetweensometendonsandunderlyingbones,STRUCTUREOFSKELETALMUSCLE(cont.),MicroscopicstructureandfunctionContractilecellsarecalledmusclefibers;connectivetissueholdsmusclefibersinparallelgroupingsFibersofthecytoskeletonformcylindersthatcontainthickmyofilaments(containingmyosin)andthinmyofilaments(containingmainlyactin),STRUCTUREOFSKELETALMUSCLE(cont.),Basicfunctional(contractileunitcalledsarcomere肌小节)SarcomeresseparatedfromeachotherbydarkbandscalledZlinesDarkstripescalledAbands(hasthickfilaments/thinfilamentsmayoverlap);lightHbandrunsacrossthemidsectionofeachdarkAbandLightstripescalledIbands(hasthinfilaments/nothickfilaments);darkZdiskextendsacrossthecenterofeachlightIband,SlidingfilamentmodelexplainsmechanismofcontractionWhenactivesitesonactinareexposed,myosinheadsbindtothem(=cross-bridges)MyosinheadsbendandpullthethinfilamentspastthemEachheadreleases,bindstothenextactivesite,andpullsagainThickandthinmyofilamentsslidepasteachothertocontractContractionrequirescalciumandenergy-richATPmolecules,STRUCTUREOFSKELETALMUSCLE(cont.),STRUCTUREOFSKELETALMUSCLE(cont.),RegionsofaskeletalmuscleOriginattachmenttothebonethatremainsrelativelystationaryorfixedwhenmovementatthejointoccursInsertionpointofattachmenttothebonethatmoveswhenamusclecontractsBodymainpartofthemuscle,FUNCTIONSOFSKELETALMUSCLE,MovementMusclesproducemovementbypullingonbonesasamusclecontractsTheinsertionboneispulledclosertotheoriginboneMovementoccursatthejointbetweentheoriginandtheinsertionGroupsofmusclesusuallycontracttoproduceasinglemovementPrimemovermainlyresponsibleforproducingagivenmovement(bicepsbrachii)Synergisthelpstheprimemoverproduceagivenmovement(brachialis)Antagonistopposestheactionofaprimemoverinagivenmovement(tricepsbrachii),FUNCTIONSOFSKELETALMUSCLE(cont.),PostureAcontinuous,low-strengthmusclecontractioncalledtoniccontraction(muscletone)enablesustomaintainbodypositionOnlyafewofamusclesfibersshortenatonetimeProducenomovementofbodypartsMaintainmuscletonecalledpostureGoodposturefavorsbestbodyfunctioningSkeletalmuscletonemaintainsgoodposturebycounteractingthepullofgravity,FUNCTIONSOFSKELETALMUSCLE(cont.),HeatproductionSurvivaldependsonthebodysabilitytomaintainaconstantbodytemperatureFeveranelevatedbodytemperatureoftenasignofillnessHypothermiaareducedbodytemperatureContractionofmusclefibersproducesmostoftheheatrequiredtomaintainnormalbodytemperature,FUNCTIONSOFSKELETALMUSCLE(cont.),FatigueReducedstrengthofmusclecontractionCausedbyrepeatedmusclestimulationwithoutadequateperiodsofrestRepeatedmuscularcontractiondepletescellularATPstoresandoutstripstheabilityofthebloodsupplytoreplenishoxygenandnutrientsContractionintheabsenceofadequateoxygenproduceslacticacid,whichcontributestomusclesorenessOxygendebttermusedtodescribethemetaboliceffortrequiredtoburnexcesslacticacidthatmayaccumulateduringprolongedperiodsofexerciseLaboredbreathingafterstrenuousexerciseisrequiredto“paythedebt”Thisincreasedmetabolismhelpsrestoreenergyandoxygenreservestopre-exerciselevels,ROLEOFOTHERBODYSYSTEMSINMOVEMENT,MusclefunctioningdependsonthefunctioningofmanyotherpartsofthebodyMostmusclescausemovementsbypullingonbonesacrossmoveablejointsRespiratory,circulatory,nervous,muscular,andskeletalsystemsplayessentialrolesinproducingnormalmovementsMultiplesclerosis,brainhemorrhage,andspinalcordinjuryareexamplesofhowpathologicalconditionsinotherbodyorgansystemscandramaticallyaffectmovement,MOTORUNIT,StimulationofamusclebyanerveimpulseisrequiredbeforeamusclecanshortenandproducemovementAmotorneuronisthespecializednervethattransmitsanimpulsetoamuscle,causingcontractionNeuromuscularjunction(NMJ)pointofcontactbetweenanerveendingandthemusclefiberMotorunitcombinationofonemotorneuronwiththemusclefibersitcontrols,MUSCLESTIMULUS,AmusclewillcontractonlyifanappliedstimulusreachesacertainlevelofintensityThresholdstimulusminimallevelofstimulationrequiredtocauseamusclefibertocontractOncestimulatedbyathresholdstimulus,amusclefiberwillcontractcompletely,aresponsecalledallornoneDifferentmusclefibersinamusclearecontrolledbydifferentmotorunitshavingdifferentthresholdstimuluslevelsAlthoughindividualmusclefibersalwaysrespondallornonetoathresholdstimulus,themuscleasawholedoesnotDifferentmotorunitsrespondingtodifferentthresholdstimulipermitamuscleasawholetoexecutecontractionsofgradedforceItallowsyoutopickupa2Lofbottleora20kgweight,TYPESOFSKELETALMUSCLECONTRACTION,TwitchandtetaniccontractionsTwitchcontractionsarelaboratoryphenomenaandnotnormalmuscleactivity;theyareasinglecontractionofmusclefiberscausedbyasinglethresholdstimulusTetaniccontractionsaresustainedmuscularcontractionscausedbystimulihittingamuscleinrapidsuccession/wiki/Tetanic_contraction,TYPESOFSKELETALMUSCLECONTRACTION(cont.),IsotoniccontractionsContractionsthatproducemovementatajointbecausethemusclechangeslengthConcentriccontractionsthemuscleshortensattheinsertionendofthemuscletomovetowardthepointoforiginEccentriccontractionsthemusclelengthensundertension,thusmovingtheinsertionawayfromtheoriginMosttypesofbodymovements(walking,running,etc.)areproducedbyisotoniccontractions,TYPESOFSKELETALMUSCLECONTRACTION(cont.),IsometriccontractionsContractionsthatdonotproducemovement;themuscleasawholedoesnotshortenAlthoughnomovementoccurs,tensionwithinthemuscleincreases,EFFECTSOFEXERCISEONSKELETALMUSCLES,Exercise,ifregularandproperlypracticed,improvesmuscletoneandposture,resultsinmoreefficientheartandlungfunctioning,andreducesfatigueMuscleschangeinrelationtotheamountofworktheynormallydoProlongedinactivitycausesdisuseatrophyRegularexerciseincreasesmusclesize,calledhypertrophy,EFFECTSOFEXERCISEONSKELETALMUSCLES(cont.),StrengthtrainingisexerciseinvolvingcontractionofmusclesagainstheavyresistanceStrengthtrainingincreasesthenumberofmyofilamentsineachmusclefiber,andasaresult,thetotalmassofthemuscleincreasesStrengthtrainingdoesnotincreasethenumberofmusclefibers(musclefibersremainthesame),Endurancetrainingisexercisethatincreasesamusclesabilitytosustainmoderateexerciseoveralongperiod;itissometimescalledaerobictrainingEndurancetrainingallowsmoreefficientdeliveryofoxygenandnutrientstoamuscleviaincreasedbloodflowEndurancetrainingdoesnotusuallyresultinmusclehypertrophy,EFFECTSOFEXERCISEONSKELETALMUSCLES(cont.),MOVEMENTSPRODUCEDBYSKELETALMUSCLECONTRACTIONS,FlexiondecreasesanangleExtensionincreasesanangleAbductionawayfromthemidlineAdductiontowardthemidlineRotationaroundanaxisCircumductionmovedistalendofapartinacircleSupinationandpronationhandpositionsthatresultfromtwistingtheforearmDorsiflexionandplantarflexionfootmovements(upwardanddownwardanklemovement)Inversionandeversionfootmovements(sideways),SKELETALMUS