MedicalNeuroscience|TutorialMAPTONEUROSCIENCECORENCC1.Thebrainisthebody'smostcomplexNCC3.G icallydeterminedcircuitsarethefoundationofthenervoussystem.NCC4.Lifeexperienceschangethenervoussystem.LearningAfterstudyoftheassignedlearningmaterials,thestudentDiscusstheneuralcentersthatgiverisetola landmedialdescendingprojectionstolowermotorneurons.DiscusstheorganizationofthemotorcortexanditscontributionstothecontrolofvolitionalCharacterizetherepresentationofthebodyinthemotorcortexandcompareittotherepresentationofthebodyintheprimarysomaticsensorycortex.DiscusspopulationcodinginthemotorGeneralfeaturesofuppermotorneuronalmosaicofmotorcontrolareasintheposteriorfrontallobethatorganizeandinitiatetheactivitiesoflowermotorcircuitsinthebrainstemandspinalcord ernstheexpressionofspecificmotorbehaviorsthatwechoosetoperform(e.g.,writing,sports,musicalperformance,speaking)someareasernspecificmotorbehaviorsoverwhichwehaveless(e.g.,emotionalnuancesinspeech,“fightorflight”thereareadditionalbrainstemcircuitsthatoperate“behindthescenes”toimplementadjustmentsofpostureandgainthereare l(skilledmovements)andmedial(supportingparallelpathwaystolowermotorneuronal1VisitBrainFforNeuroscienceCoreConcepts(?2012SocietyforNeuroscience)thatofferfundamentalpr aboutthebrainandnervoussystem,themostcomplexlivingstructureknownintheuniverse.forvoluntarymovement,thereisavolitionalorsomaticmotorsystem(thisissometimescalledthe“pyramidalmotorsystem”,namedforthepyramidaltract,themajorsubcorticaloutflowofthemotorcortex)(seeFigure17.12) lcomponent: ernsthet(“fractionated”)movementsofthelowerfaceanddistalextremities,conveyedviathecorticobulbarandcorticospinaltractsSeetutorialon“UpperMotorNeuronalControlofFacialmedialcomponent: ernsposturalcontrolandorientingmovementsofheadandneckconveyedviaprojectionsfrombrainstemnuclei(note:althoughthesefunctionsare,strictlyspeaking,non-volitional,weludethemheretoemphasizetheirserviceofother,morespecificvolitionalmovements)thisla l/medialdivisionoflaborisareflectionoftheorganizationofmotorneuronsintheventralhornofthespinalcordfortheexpressionofmovementsthatarelessvolitional,ofteninthecontextofemotionalexperience,thereareadditionalpathwaysfromthecortexandbrainstemthatmediateemotionalmotorbehavior;theseneuralcentersandpathwayscomprisean“emotionalmotorsystem”(seeFigure29.2) lcomponent:ernstheexpressionofspecificsomaticandvisceralmotorbehaviorsviadiffuseprojectionsthatarenotpartofthepyramidaltractmedialcomponent:modulatesthegainofbrainstemandsegmental/intersegmentalspinalreflexes MotorControlCentersintheCerebralCortex: lprojectionsforvolitionalmotor“Motorcortex”referstothemosaicofcorticalareasintheposteriorfrontallobethataremainlyconcernedwiththenningandexecutionofvolitionalmovements;theseludetheprimarymotorcortexandthepremotorcortex(seeFigureeachofthesedivisionsofthemotorcortexgivsetodescendingprojectionstolowermotorneuronalcircuitsinthebrainstemandspinalcordcollectively,themotorcortexreceivesinputfromthemotornucleiofthethalamus(ventralanterior/ventralla lcomplex)andsomaticsensoryandvisualinputfromsomaticsensoryandvisualcorticalareas(“where”pathway)intheparietallobeprimarymotorcortex(Brodmann’sArealocatedintheanteriorbankoftheprecentraltheoriginofalargefractionofthecorticospinal(pyramidal)mostdescendingprojections(whicharisefromlayer5)terminateonthedendritesofinterneuronsinlocal-circuitneuronalpoolsofthebrainstemandspinalcordsomeoutputneurons(ludingtheexceptionallylargzcells)monosynapticexcitatoryconnectionontoαmotor2FigurereferencestoPurvesetal.,Neuroscience,5thEd.,SinauerAssoc.,.,2012.[clickthisareais“primary”becauseithasthelowestthresholdfortheelicitationofmovementswithelectricalstimulationofanyareainthecerebralcortextheprimarymotorcortex ernstheexecutionofvolitionalmovements,particularlythosethatinvolvethedistalextremities alspacesomatotopyintheprimarymotoralongthelengthofthecentralsulcus,thereisacruderepresentationofthebody’smusculature(seeFigurealthoughsimilartothesomatotopicmapintheprimarysomaticsensorycortex,thetopographicmapintheprimarymotorcortexislesscolumnarand,therefore,muchlessprecise()e.g.,ratherthanasystematicmapofeachdigitinsequence(suchaistsinS1),thereisageneralhandregionthatcannotbesubdividedintorepresentationsofindividualdigits(i) neuronsthatareconnectedtolowermotorneuronsthaternthemovementsofdifferentdigitsareinterspersedandhighlyinterconnectedwithinthishandregionthisarrangementallowsforthedynamicassemblyoffunctionalensemblesofneuronsthatorchestratethecoordinatedmovementsofthedigitsdynamicassemblyoffunctionaworksissubjecttoexperience-dependentmodificationwhatisrepresentedintheprimarymotorcortex?(anongoingdebate;seeBox17B)movements!(notmuscles)…andmaybeeventhe(goals)of() encodesmovementsthatengagethehand,lowerface(mouth),andthecoordinatedactivityofhandandmouth( skilled entralalindividualswithselectivelesionsoftheprimarymotorcortexcanreachtograbsmallobjects,buthavedifficultiespickingthemupwiththeirfingerssomeresidualdigitfunctionmayreflectpreservationofsynergisticprojectionsfromotherpartsofthemotorcortex(andmaybetherednucleus)howismovementcoding“tuningproperties”ofanycorticospinalneuronarebroad,eventhoughmovementsmaybehighlyspecializedandspecific()movementsareencodedbytheconcurrentdischargesoflargepopulationsofneuronsinthemotorcortex;thisisanexampleofa“populationcode”inneuralprocessing(seeFigure17.8)StudyWhatfeaturesbestdifferentiatesthebodymapintheprecentralgyrus(primarymotorcortex)fromthepostcentralgyrus(primarysomaticsensorycortex)?Thecentralsegmentoftheprecentralgyrusrepresentsthecontralalfoot,whilethecentralsegmentofthepostcentralgyrusrepresentsthecontralalface.Theinferiorsegmentoftheprecentralgyrusrepresentsthecontralalface,whilethecentralsegmentofthepostcentralgyrusrepresentsthecontralalhand.Themedialportionoftheprecentralgyrus(intheparacentrallobule)representsthecontralalhand,whilethemedialportionofthepostcentralgyrusrepresentsthecontralalface.Thebodymapintheprecentralgyrusfaithfullyrepresentsthedetailedstruc