Chapter9MotorSystem-2SpinalReflex,DescendingPathwaysandCerebellumContentSpinalReflexesFunctionofBrainStemFunctionofCerebellumReferenceP164-180P464-470P473-475P673-684P691-707Section1.SpinalReflexesSomaticreflexesmediatedbythespinalcordMayoccurwithouttheinvolvementofhigherbraincentersWasfacilitatedorinhibitedbybrainForexampleStretchreflexDeeptendonreflexCrossedextensorreflexSuperficialreflex

PartIStretchReflex1AnatomyofMuscleSpindle3-10intrafusalmusclefibersdetectchangeinthelengthofthemuscle--stretchreceptorsthatreportthestretchingofthemuscletothespine.ThecentralregionandperipheralregionoftheintrafusalfibersAnatomyofMuscleSpindleIntrafusalfibersarewrappedbytwotypesofafferentendingsPrimarysensoryendingsTypeIafibersInnervatethecenterofthespindleSecondarysensoryendingsTypeIIfibersAssociatedwiththeendsofthenuclearchainfiberComponentsofmusclespindleStaticintrafusalfibersDynamicintrafusalfiberAfferentaxonsIaIIStaticintrafusalfibersPrimaryendingSecondaryending}}NuclearBagFiberNuclearChainFiberAnatomyofMuscleSpindlePrimarysensoryendingsTypeIafibersStimulatedbyboththerateandamountofstretch(dynamicresponse)AnatomyofMuscleSpindleSecondarysensoryendingsTypeIIfibersstimulatedonlybydegreeofstretch(staticresponse)AnatomyofMuscleSpindleThecontractileregionoftheintrafusalmusclefibersarelimitedtotheirendsonlytheseareascontainactinandmyosinfilamentsareinnervatedbygamma(

)efferentfibers2.MusclestretchreflexMusclestretchreflexDefinition:Wheneveramuscleisstretched,excitationofthespindlescausesreflexivecontractionofthesamemusclefromwhichthesignaloriginatedandalsoofcloselyalliedsynergisticmuscle.

Thebasiccircuit:SpindleIaorIInervefiberdorsalrootofthespinalcordsynapseswithanteriormotorneurons

-motorN.F.thesameM.fromwhencetheM.spindlefiberoriginated.CircuitoftheStrengthReflexDorsalrootVentralrootMusclespindleTendonMusclefiber

-mnTheStretchReflexExcitingamusclespindleoccursintwowaysApplyingaforcethatlengthenstheentiremuscleActivatingthemotorneuronsthatstimulatethedistalendsoftheintrafusalfiberstocontact,thusstretchingthemid-portionofthespindle(internalstretch)TheStretchReflexWhateverthestimulus,whenthespindlesareactivatedtheirassociatedsensoryneuronstransmitimpulsesatahigherfrequencytothespinalcordTheStretchReflexThereflexivemusclecontractionthatfollowsresistsfurtherstretchingofthemuscleTheStretchReflexBranchesoftheafferentfibersalsosynapsewithinter-neuronsthatinhibitmotorneuronscontrollingtheantagonisticmusclesInhibitionoftheantagonisticmusclesiscalledreciprocalinhibitioncausestheantagoniststorelaxTendonreflex(dynamicstretchreflex)

Causedbyrapidstretchofthemuscle,asknee-jerkreflex;

TransmittedfromtheIAsensoryendingoftheM.S.

Causesaninstantaneous,strongreflexivecontractionofthesamemuscle;

OpposingsuddenchangesinlengthoftheM.;Amonosynapticpathwaybeingoverwithin0.7ms;

ThetypesoftheStretchFlex2)

Muscletonus(staticstretchreflex):

Causedbyaweakerandcontinuesstretchofthemuscle,

TransmittedfromtheIAandIIsensoryendingoftheM.S.

Multiplesynapticpathway,continuesforaprolongedperiod.

Non-synchronizedcontraction,

M.C.foratleastmanysecondsorminutes,maintainingthepostureofthebody.ThetypesoftheStretchFlexTheStretchReflexmostimportantinlargeextensormuscleswhichsustainuprightpostureContractionsoftheposturalmusclesofthespinearealmostcontinuouslyregulatedbystretchreflexes(Muscletonus)3GammaimpactonafferentresponseMusclespindle:motorinnervationGammamotoneurons:Innervatethepolesofthefibers.g-LOOPga1aDescendinginfluence(UMN)MUSCLEMusclespindleActivationoftheg-loopresultsinincreasedmuscletoneFunctionalsignificanceofgammaimpactonspindleactivityThetensionofintrafusalfibersismaintainedduringactivecontractionbygammaactivity.Thesystemisinformedaboutverysmallchangesinmusclelength.Part2.TheDeepTendonReflexStructureandInnervationofGolgiOrganLocatedinthemuscletendonjunction.Connectivetissueencapsulatingcollagenfibersandnerveendings.Attachedto10-20musclefibersandseveralMUs.Ibafferentfiber.sensitivetotensionGolgitendonorgan:responsepropertiesLessfrequentthanmusclespindleSensitivetothechangeoftensioncausedbythepassivestretchoractivecontractionTheDeepTendonReflexWhenmuscletensionincreasesmoderatelyduringmusclecontractionorpassivestretching,GTOreceptorsareactivatedandafferentimpulsesaretransmittedtothespinalcordTheDeepTendonReflexSimultaneously,motorneuronsinthespinalcordsupplyingthecontractingmuscleareinhibitedandantagonisticmuscleareactivatedTheDeepTendonReflexcausemusclerelaxationandlengtheninginresponsetothemuscle’scontractionoppositeofthoseelicitedbystretchreflexeshelpensuresmoothonsetandterminationofmusclecontractionimportantinactivitiesinvolvingrapidswitchingbetweenflexionandextensionsuchasinrunningComparespindleandgolgiComparespindleandgolgiPart3.TheCrossedExtensorReflexThereflexoccurwhenyousteponasharpobjectThereisarapidliftingoftheaffectedfoot(ipsilateralwithdrawalreflex),whilethecontralateralresponseactivatestheextensormusclesoftheoppositeleg(contralateralextensorreflex)supporttheweightshiftedtoitPart4.SuperficialReflexeselicitedbygentlecutaneousstimulationdependentuponfunctionaluppermotorpathwaysBabinskireflexBabinskireflex-anUMNsignAdultresponse-plantarflexionofthebigtoeandadductionofthesmallertoesPathological(Infant)response-dorsoflexion(extension)ofthebigtoeandfanningoftheothertoesIndicativeofuppermotorneurondamageConcept:

Whenthespinalcordissuddenlytransectedintheupperneck,essentiallyallcordfunctions,includingthecordreflexes,immediatelybecomedepressedtothepointoftotalsilence.(spinalanimal)

Part5.Spinalcordtransectionandspinalshock(2)Duringspinalshock:completelossofallreflexes,notone,paralysiscompleteanesthesia,noperistalsis,bladderandrectalreflexesabsent(nodefecationandmicturition)nosweatingarterialbloodPressuredecrease（40mmHg）

(3)thereason:

Thenormalactivityofthespinalcordneuronsdependsoncontinualtonicexcitationfromhighercenters(thereticulospinal-,vestibulospinal-corticospinaltracts).(4)Therecoveryofspinalneuronsexcitability.

SectionII.RoleofthebrainstemSupportoftheBodyAgainstGravity–RolesoftheReticularandVestibularnucleiAreasinthecatbrainwherestimulationproducesfacilitation(+)orinhibition(-)ofstretchreflexes.1.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.Facilitatedandinhibitoryarea1.Facilitatedarea—rolesofthereticularandvestibularnuclei.：(1)

ThepontinereticularnucleiLocatedslightlyposteriorlyandlaterallyintheponsandextendingtothemesencephalonTransmitexcitatorysignalsdownwardintothecord(thepontinereticulospinaltract)motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.(2)ThevestibularnucleiselectivelycontroltheexcitatorysignalstothedifferentantigravityM.tomaintainequilibriuminresponsetosignalsfromthevestibularapparatus.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.MOTORCORTEXMOTORTRACTS&LOWERMOTORNEURONSKELETALMUSCLEMIDBRAIN&REDNUCLEUS(RubrospinalTract)PONS&MEDULLARETICULARFORMATION(ReticulospinalTracts)VESTIBULARNUCLEI(VestibulospinalTract)LOWER(ALPHA)MOTORNEURONTHEFINALCOMMONPATHWAYUPPERMOTORNEURON(CorticospinalTracts)TerminateonthemotorneuronsthatexcitingantigravityM.ofthebody(theM.ofvertebralcolumnandtheextensorM.ofthelimbs).Haveahighdegreeofnatural(spontaneous)excitability.Receiveespeciallystrongexcitatorysignalsfromvestibularnucleiandthedeepnucleiofthecerebellum.CausepowerfulexcitationoftheantigravityMthroughoutthebody(facilitateastandingposition),supportingthebodyagainstgravity.1.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.PropertiesoftheFacilitatedArea2.Inhibitoryarea–medullaryreticularsystem

Extendtheentireextenttothemedulla,lyingventrallyandmediallynearthemiddle.Transmitinhibitorysignalstothesameantigravityanteriormotorneurons(medullaryreticulospinaltract).1.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.MOTORCORTEXMOTORTRACTS&LOWERMOTORNEURONSKELETALMUSCLEMIDBRAIN&REDNUCLEUS(RubrospinalTract)PONS&MEDULLARETICULARFORMATION(ReticulospinalTracts)VESTIBULARNUCLEI(VestibulospinalTract)LOWER(ALPHA)MOTORNEURONTHEFINALCOMMONPATHWAYUPPERMOTORNEURON(CorticospinalTracts)Receivecollateralsfromthecorticospinaltract;therubrospinaltracts;andothermotorpathways.activatethemedullaryreticularinhibitorysystemtobalancetheexcitatorysignalsfromtheP.R.T.,MaintainnormaltenseofthebodyM.undernormalconditions.

1.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.Areasinthecatbrainwherestimulationproducesfacilitation(+)orinhibition(-)ofstretchreflexes.1.motorcortex;2.Basalganglia;3.Cerebellum;4.Reticularinhibitoryarea;5.Reticularfacilitatedarea;6.Vestibularnuclei.DecerebrateRigidity:transectionofthebrainstematmidbrainlevel(abovevestibularnucleiandbelowrednucleus)Symptomsinclude: extensorrigidityorposturinginbothupperandlowerlimbsDecerebrateRigidityResultsfrom:

lossofinputfrominhibitorymedullaryRF(activityofthiscenterisdependentoninputfromhighercenters).activefacilitationfrompontineRF(intrinsicallyactive,andreceivesafferentinputfromspinalcord).Theextensorrigidityisg-loopdependentsectionthedorsalrootsinterruptstheg-loop,andtherigidityisrelieved.Thisisg-rigidity.ga1aDescendinginfluence(UMN)MUSCLEMusclespindleActivationoftheg-loopresultsinincreasedmuscletoneSectionIII.ThecerebellumanditsmotorfunctionsCerebellarInput/OutputCircuitFunctionofthecerebellumBasedoncerebralintentandexternalconditionstracksandmodifiesmillisecond-to-millisecondmusclecontractionsproducesmooth,reproduciblemovementsWithoutnormalcerebellarfunction,movementsappearjerkyanduncontrolledFunctionalDivisions-cerebellumVestibulocerebellum(flocculonodularlobe)input-vestibularnucleioutput-vestibularnucleiThevestibulocerebellumcontrollingthebalancebetweenagonistandantagonistM.contractionsofthespine,hips,andshouldersduringrapidchangesinbodypositions.MethodDuringrunningReceivethesignalsfromtheperipheryhowrapidlyandinwhichdirectionsthebodypartsaremovingCalculatetheratesanddirectionwherethedifferentpartsofbodywillbeduringthenextfewms.anticipatorycorrection(feedforwardcontrol)thekeytothebrains’sprogressiontothenextsequentialmovement.Function1:Controloftheequilibriumandposturalmovements.Function2regulatetheeyemovement

Throughvestibulo-ocularreflexkeeptheeyesstillinspacewhentheheadmovesDamageoftheflocculonofularloberesultinpositionalnystagmus(位置性眼震顫）TheVOR:DefinitionAeyemovementreflexStimulatedbyheadmovementsMovestheeyesoppositeoftheheadHelpskeeptheretinalimagestabilizedTheVORcontributestoclearvisionduringheadmovementsSpinocerebellum(vermis&intermediate)Spinocerebellum(vermis&intermediate)input-somaticsensoryinformationviaspinocerebellartractsBranchfromcorticospinaltract

OutputThamalus–motorcortex-fastigial(頂）andinterposed（中間核）nuclei→vestibularnuclei,reticularformationandrednucleus→vestibulospinaltract,reticulospinaltractandrubrospinaltract→motorneuronsofanteriorhornFunctionofspinocerebellumProvidethecircuitryforcoordinatingthemovementsofthedistalportionsofthelimbs,especiallythehandsandfingersComparedthe“intentions”fromthemotorcortexandrednucleus,withthe“performance”fromtheperipheralpartsofthelimbsSendcorrectiveoutputsignalstothemotorneuronsProvidessmooth,coordinatemovementsFeedbackcontrolCerebrocerebellum(lateralzone)input-fromthecerebralcortexviaarelayinpontinenucleioutput-todentatenucleus→dorsalthalamusandrednucleus→primarymotorcortex→corticospinaltract→motorneuronsofanteriorhornCerebrocerebellum(functions)PlanningandprogrammingofsequentialmovementsPanning:beginsinthesensoryandpromotorareaofthecortexandtransmittedtothecerebrocerebellumProgramming:Cerebroc