六、肌細ContractionofMuscle(肌束(肌纖維/肌細胞(肌原纖維(肌節/肌小節(肌絲

Productionofbody運動單位(motor（一）骨骼肌神經-肌接頭的傳神經-肌接頭（NMJ）微細接頭前接頭后膜或終板接頭間神經肌接頭（NMJ）興奮傳*ActivationofACh-gatedionchannel(nAChR)resultsinEnd-PlatePotential(EPP)神經肌接頭傳遞（電-化學-電過程神經沖神經沖動到達末梢，接頭前膜去電壓門控Ca2＋通道開放、Ca2＋內囊泡向接頭前膜囊泡向接頭前膜移動、融合、破ACh釋放至接頭乙NaNa＋內流使終板膜去極化NMJ興奮傳遞的特征是電-化學-電的N末梢AP→ACh＋受體→EPP→肌膜具1對1的關奮和收縮一次（因每次ACh釋放的量，產生的影響NMJ興奮傳遞的因素： 阻斷ACh受體：箭毒(curare)α（Flexadil，三碘季胺酚） 新斯的明，Sarin,VX,etc。3自身免疫性疾病：Myasthenia（抗體破壞ACh受體),Lambert-Eatonsyndrome（抗體破壞N末梢Ca2+4接頭前膜ACh釋放↓：肉毒桿菌毒（二）橫紋肌細胞的興奮-收縮耦興奮-收縮耦聯的結構基道）Longitudinaltubularsystem：LTriad：T管+興奮-收縮耦聯的關鍵離子——L型鈣通道和鈣釋放通骨骼肌細胞和心肌細胞的鈣釋骨骼肌細胞和心肌細胞的鈣回鈣瞬變（calciumtransient）引起肌肉的收縮和舒興奮-①肌膜電興奮的傳導②肌膜和T管上L型Ca2+通道激活③肌漿網上Ryanodine受體激活，肌漿網Ca2+釋放(calcium④觸發肌絲滑行，肌細胞收縮（三）肌絲的分子組粗肌絲（thick肌球蛋白橫橋（cross-

細肌絲（thin肌動蛋白原肌球蛋白肌鈣蛋白（troponin橫紋肌收縮的原理—Z

MlineHband

ZA直

白的相互ICT ICTs原肌球蛋白細肌絲上的結合肌肌節縮短,肌細胞收Sourcesof肌肉的舒張(Muscle—mechanismsthatrestoresarcoplamicBacktocalciumCa2+pumpinsarcoplasmicreticulum~100%inskeletal~70%incardiacOutofthe①Na+-Ca2+exchangerincell②Ca2+pumpincellDiseasesassociatedwithabnormalregulationtheintracellularCa2+inskeletal Malignanthyperthermia:geneticdefectinryanodinereceptor,1in15,000children,1in50,000adults;Halothane/etherorsuccinylcholinestimulateCa2+releasefromSR,resultingmusclerigidityandhyperthermiaCentralcoredisease:geneticdefectinryanodinereceptor;SRreleases/leakCa2+,whichisthenaccumulatedbymitochondria,resultinginmitochondrialCa2+overloadandhencelossofmitochondriaandmuscleweaknessBrody’sdisease:geneticdefectinSRCa2+pump(SERCA):painlessmusclecram duringexerciseduetoslowedCa2+Summary:SequentialeventsofThesarcolemmaisdepolarizedandtheactionpotential(AP)propagates;TheactionpotentialspreadsinsidealongtheT-tubules;APistransmittedfromT-tubuletoterminalsacsofsarcoplasmicreticulum;Calciumisreleasedfromsarcoplasmicreticulumintosarcoplasm;Calciumbindstotroponinleadingtocooperativeconformationalchangesintroponin-tropomyosinsystem;Theinhibitionofactinandmyosininteractionisreleased;Crossbridgesofmyosinfilamentsareattachedtoactinfilaments;Tensionisexertedand/orthemuscleshortensbytheslidingfilamentCalciumispumpedbackintosarcoplasmicreticulum;Crossbridgesaredetachedfromthethinfilaments;Troponin-tropomyosinregulatedinhibitionofactinandmyosininteractionisActivetensiondisappearsandtherestlengthis（四）影響橫紋肌收縮效能的肌肉收縮的形單收縮、復合收縮、強直等張收IsotonicForce等長ForceIsometric單收縮、復合收縮與強直收 前負荷 后負荷(After-determineslengthofcross-bridge cyclesandhencetotalnumberofcross-bridgesinteractingwiththinfilaments;肌肉的收縮性 affectingthoseproperties前負荷（Preload)：肌肉收縮前所承受的負荷,決定了肌節最適初長（2.0-2.2m）時，粗細肌絲 佳，肌 小于最適初長時，細肌絲可縮短距離↓→效能↓大部分骨骼肌的靜態長度即是其最適初長，Optimalinitiallength也稱Resting肌 Optimalinitiallength(resting后負荷↓→肌縮速度、幅度↑和張力↓后負荷過大，雖肌縮張力↑，但肌縮速度↓，不利作功后負荷過小，雖肌縮速度、幅度↑，但肌↓，也不利作TypesofskeletalTypeImuscleTypeIImuscleOtherATPaserateofsarcoplasmicGlycolyticOxidativeFine,skilled（五）平滑肌的收縮和舒MorphologicalMorphologicalandfunctionalMechanismsof形態學特involuntarymuscle;innervatedbyANS;foundprimarilyinthewallsofhollowSpindle-shapedcellstypicallyarrangedinNot-tubules&littlesarcoplasmic eres(soarenotstriated)butaremadeupofthick&myofilaments.ThinfilamentsinsmoothmuscledonotcontainCalciumbindstocalmodulin.Thecalcium-calmodulincomplex'activates'myosinwhichthenbindstoactin&contraction(swivellingofcross-bridges)Twotypesofsmooth多個單位平滑visceral,orunitary,smoothfoundinthewallsofholloworgans(e.g.,smallbloodvessels,digestivetract,urinarysystem,&reproductivesystem)multiplefiberscontractasaunit(becauseimpulsestraveleasilyacrossgapjunctionsfromcelltocell)&,insomecases,areself-excitable(generatespontaneousactionpotentials&contractions)multiunitsmoothconsistsofmotorunitsthatareactivatedbynervousfoundinthewallsoflargebloodvessels,intheeye(adustingtheshapeofthelenstopermit modation&thesizeofthepupiltoadjusttheamountoflightenteringtheeye),&atthebaseofhairfollicle(the'goosebump'muscles)Openingofvoltage-gatedcalciumchannelsaccountsfortheactionpotentialofmostsmoothmusclecells.平滑肌收縮與舒IonLittleappreciatedfactofHumanbeings(andotherlivingorganisms)arerunbyelectricity,and"ionchannels"arethecoreofourelectricalIonchannelsareeverywhere&arepresentinalmosteveryTransportofionsandRegulationofelectricalpotentialacrosstheIonYetanothertypeofmembranePoresinthemembranethatopenandcloseinaregulatedmannerandallowpassageofions“Dispose”ofthe Passivetransporters:IonsflowfromhightolowNoenergyisused;IfthereisnogradientionswillnotflowChannelIonchannelsarenotopencontinuouslybutopenandcloseinastochasticorrandomfashion.Ionchannelfunctionmaybedecreasedbydecreasingtheopentime(o),increasingtheclosedtime(c),decreasingthesinglechannelcurrentamplitude(i)ordecreasingthenumberofchannels(n).Whatgatesionchannel