解剖学――肌肉_Muscular

TheMuscularSystemINTRODUCTIONMusculartissueenablesthebodyanditspartstomoveThreetypesofmuscletissueexistinbody:SkeletalCardiacSmoothMovementcausedbymusclecells(calledfibers):shorteningorcontractingMusclemovementoccurswhenchemicalenergy(obtainedfromfood)isconvertedintomechanicalenergyMUSCLETISSUETypesofmuscletissueSkeletalmuscle—alsocalledstriatedorvoluntarymuscleMicroscoperevealscrosswisestripesorstriationsContractionscanbevoluntarilycontrolledCardiacmuscle—composesbulkofheartCardiacmusclefibersarebranchedHasdarkbandscalledintercalateddisksIntercalateddiscssupportsynchronisedcontractionofcardiactissueCardiacmusclefiberinterconnectionsallowhearttocontractefficientlyasaunitMUSCLETISSUE(cont.)Typesofmuscletissue(cont.)Nonstriatedmuscle,orinvoluntarymuscle—alsocalledsmoothorvisceralmuscleLackscrossstripesorstriationswhenseenunderamicroscope;appearssmoothFoundinwallsofhollowstructures,suchasdigestivetract,bloodvessels,etc.ContractionsnotundervoluntarycontrolFunction—allmusclefibersspecializeincontraction(shortening)STRUCTUREOFSKELETALMUSCLEMuscleorgans—mainlystriatedmusclefibersandconnectivetissueConnectivetissueforms“wrappers”aroundeachmusclefiber,aroundfascicles一簇(groups)ofmusclefibers,andaroundtheentiremuscleFascia筋膜surroundsmuscleorgansandnearbystructuresMostskeletalmusclesextendfromoneboneacrossajointtoanotherboneSTRUCTUREOFSKELETALMUSCLE(cont.)Muscleorgans(cont.)•Musclesattachtobonebytendons—strongcordsorsheetsoffibrousconnectivetissuethatextendfromthemuscleorgan;•sometendonsenclosedinsynovial-linedtubes(tendonsheaths)andarelubricatedbysynovialfluid•Bursae—smallsynovial-linedsacscontainingasmallamountofsynovialfluid;locatedbetweensometendonsandunderlyingbonesSTRUCTUREOFSKELETALMUSCLE(cont.)MicroscopicstructureandfunctionContractilecellsarecalledmusclefibers;connectivetissueholdsmusclefibersinparallelgroupingsFibersofthecytoskeletonformcylindersthatcontainthickmyofilaments(containingmyosin)andthinmyofilaments(containingmainlyactin)STRUCTUREOFSKELETALMUSCLE(cont.)Basicfunctional(contractileunitcalledsarcomere肌小节)SarcomeresseparatedfromeachotherbydarkbandscalledZlinesDarkstripescalledAbands(hasthickfilaments/thinfilamentsmayoverlap);lightHbandrunsacrossthemidsectionofeachdarkAbandLightstripescalledIbands(hasthinfilaments/nothickfilaments);darkZdiskextendsacrossthecenterofeachlightIband•Slidingfilamentmodelexplainsmechanismofcontraction•Whenactivesitesonactinareexposed,myosinheadsbindtothem(=cross-bridges)•Myosinheadsbendandpullthethinfilamentspastthem•Eachheadreleases,bindstothenextactivesite,andpullsagain•Thickandthinmyofilamentsslidepasteachothertocontract•Contractionrequirescalciumandenergy-richATPmoleculesSTRUCTUREOFSKELETALMUSCLE(cont.)STRUCTUREOFSKELETALMUSCLE(cont.)Regionsofaskeletalmuscle•Origin—attachmenttothebonethatremainsrelativelystationaryorfixedwhenmovementatthejointoccurs•Insertion—pointofattachmenttothebonethatmoveswhenamusclecontracts•Body—mainpartofthemuscleFUNCTIONSOFSKELETALMUSCLEMovementMusclesproducemovementbypullingonbonesasamusclecontractsTheinsertionboneispulledclosertotheoriginboneMovementoccursatthejointbetweentheoriginandtheinsertionGroupsofmusclesusuallycontracttoproduceasinglemovementPrimemover—mainlyresponsibleforproducingagivenmovement(bicepsbrachii)Synergist—helpstheprimemoverproduceagivenmovement(brachialis)Antagonist—opposestheactionofaprimemoverinagivenmovement(tricepsbrachii)FUNCTIONSOFSKELETALMUSCLE(cont.)PostureAcontinuous,low-strengthmusclecontractioncalledtoniccontraction(muscletone)enablesustomaintainbodypositionOnlyafewofamuscle'sfibersshortenatonetimeProducenomovementofbodypartsMaintainmuscletonecalledpostureGoodposturefavorsbestbodyfunctioningSkeletalmuscletonemaintainsgoodposturebycounteractingthepullofgravityFUNCTIONSOFSKELETALMUSCLE(cont.)HeatproductionSurvivaldependsonthebody’sabilitytomaintainaconstantbodytemperatureFever—anelevatedbodytemperature—oftenasignofillnessHypothermia—areducedbodytemperatureContractionofmusclefibersproducesmostoftheheatrequiredtomaintainnormalbodytemperatureFUNCTIONSOFSKELETALMUSCLE(cont.)FatigueReducedstrengthofmusclecontractionCausedbyrepeatedmusclestimulationwithoutadequateperiodsofrestRepeatedmuscularcontractiondepletescellularATPstoresandoutstripstheabilityofthebloodsupplytoreplenishoxygenandnutrientsContractionintheabsenceofadequateoxygenproduceslacticacid,whichcontributestomusclesorenessOxygendebt—termusedtodescribethemetaboliceffortrequiredtoburnexcesslacticacidthatmayaccumulateduringprolongedperiodsofexerciseLaboredbreathingafterstrenuousexerciseisrequiredto“paythedebt”Thisincreasedmetabolismhelpsrestoreenergyandoxygenreservestopre-exerciselevelsROLEOFOTHERBODYSYSTEMSINMOVEMENTMusclefunctioningdependsonthefunctioningofmanyotherpartsofthebodyMostmusclescausemovementsbypullingonbonesacrossmoveablejointsRespiratory,circulatory,nervous,muscular,andskeletalsystemsplayessentialrolesinproducingnormalmovementsMultiplesclerosis,brainhemorrhage,andspinalcordinjuryareex