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No 28 1 MotorPathways TheMotor descending Pathways Themotorpathwaysareconcernedwithmotorfunction andcomposedofuppermotorneuronsandlowermotorneurons Theuppermotorneuronsaretheefferentneuronsfromthecerebralcortextothemotornucleiofcranialnervesandanteriorhornsofspinalcord Thelowermotorneuronsarethenervesinthemotornucleiofcranialnervesandtheanteriorhornsofspinalcord Thecellbodiesandaxonsoflowermotorneuronsserveasthefinalcommonpathwayconnectingmotorimpulses Themotorpathwaysincludepyramidalandextrapyramidalsystems ThePyramidalSystem Itisconcernedwiththevoluntarymovementoftheskeletalmusclesandiscomposedoftwoordersofneurons i e theupperandlowermotorneurons Theuppermotorneuronsarecomposedofthegiantpyramidalcells Betzcells andotherpyramidalcellsofvarioussizedwhicharelocatedintheprecentralgyrusandtheanteriorpartofparacentrallobuleandthepyramidalcellsinthesomeareasoffrontal parietallobes Theiraxonsformthedescendingpyramidaltract amongwhich thefibersendinginthecranialmotornucleiaredesignatedasthecorticonucleartractandthoseterminatingintheanteriorhornofthespinalcordascorticospinaltract Thelowermotorneuronsincludethecranialmotorcellsofthebrainstemandspinalmotorcellsofthespinalcord 1 Thecorticospinaltract Theuppermotorneuronsarethepyramidalpyramidalcellsinthesuperiorandmiddlepartsoftheprecentralgyrusandtheanteriorpartofparacentrallobule Theaxonsarisingfromtheseuppermotorneuronsformthecorticospinaltract Ittraversestheposteriorlimbofinternalcapsule theintermediate3 5ofthecruscerebri thebasilarpartofthepons andtheventralpartofthemedullaoblongata Inthecaudalpartofthemedullaoblongatathegreaterpart 75 90 ofthetractcrossestotheoppositesidetoformthepyramidaldecussationandcontinuesasthelateralcorticospinaltractinthelateralfuniculusofthespinalcord Thefibersofthelateralcorticospinaltractterminateintheanteriorgrayhornsofallthespinalsegmentscontrollingthemovementsofmusclesofthelimbs Thenon crossedfiberscontinueastheanteriorcorticospinaltractdirectlyintotheanteriorfuniculusofthesamesideandcrossthemedianplaneintheanteriorwhitecommissureandsynapse asdothoseofthelateraltract directlyorindirectlywiththemotorneuronsoftheanteriorgrayhorn Theanteriorcorticospinaltractisgenerallybelievedtoexistabovethelevelofthemid thoracicsegments controllingthemusclesoftrunkandlimbs Asmallpartintheanteriorcorticospinaltractdonotcrossestotheoppositeside terminatingintheipilateralanteriorhornsofthespinalcord Theseuncrossedfibersinnervatethetrunkmusclesbywayofthemotorcellsoftheanteriorgrayhorn Sothatthetrunkmusclesarecontrolledbybilateralmotorcortexofthehemisphere Thelowermotorneuronsarethelargemultipolarcellsoftheanteriorgrayhorn Theygiverisetothemotorfibersthatleavethespinalcordthroughtheanteriorrootstobedistributedbywayofthespinalnervestotheskeletalmuscles Becauseoftheinhibitoryfunctionsoftheuppermotorneuronstothelowerones therearedifferentclinicalsignsinthecasesofdamagetotheupperorlowermotorneurons 2 Thecorticonucleartract Theuppermotorneuronsarethegiantpyramidalandcertainothersmallerpyramidalneuronsintheinferiorpartoftheprecentralgyrus Theaxonsarisingfromtheseuppermotorneuronsformthecorticonucleartract Inthecourseofdescendingthroughthegenuofinternalcapsuleandthebrainstem itgiverisetothecollateralsofthebilateraloculomotor trochlear trigeminalmotor ambiguous accessorynucleiandsuperiorpartofthefacialnucleus andtothecontralateralhypoglossalnucleusandtheinferiorpartofthefacialnucleus So thehypoglossalnucleusandinferiorpartofthefacialnucleusreceivethefibersonlyfromthecontralateralcorticonucleartract Thelowerneuronsarethecellsintheabovecranialmotornuclei Thelowerneuronsgiverisetoaxonsjoiningthecorrespondingcranialnervesthatcontrolthemovementsoftheinnervatedskeletalmuscles Becausetheinferiorpartofthefacialnucleusandhypoglossalnucleusreceivefibersjustfromthecontralateralcorticonucleartract theinjuryoftheunilateralcorticonucleartractcanusuallycauseparalysisofthecontralateralglossalmusclesandfacialmusclesbelowthepalpebralfissure Thisisdesignatedassupranuclearparalysis Paralysisoftheunilateralfacialmusclescausedbyaninjuryofthehomolateralfacialnerveistermedasinfranuclearparalysis Form1 Thecomparisonofexpressionsafterinjurytotheupperandlowermotorneurons TheExtrapyramidalSystem Itisacommonnameforthedescendingpathwaysregulatingandcontrollingthevoluntarymovementsexceptthepyramidalsystem Functions Themainfunctionsoftheextrapyramidalsysteminmanaretoregulatethetonicityofthemuscles coordinatethemuscularactivities maintainthenormalbodypostureandproducehabitualandrhythmicmovements Forexample ridingandrunningareinitiatedinthebeginningbythepyramidalsystem butarecontrolledbytheextrapyramidalsystemwhenthemotionslaterbecomehabitualandrhythmic Sotheskeletalmuscularmovementsarecontrolledbythecortexofthehemispherebywayofthepyramidalandextrapyramidalsystemstoproducecoordinated precisemotions Thetwosystemshavethecoordinatedanddependentfunctionswitheachother Structuresoftheextrapyramidalsystemareverycomplicatedincludingcerebralcortex somaticmotorareaandsomaticsensoryarea corpusstriatum dorsalthalamus subthalamicnucleus tectumofmidbrain rednucleus substantianigra pontinenucleus vestibularnucleus cerebellum reticularformationofbrainstem andtheirfibrousconnections 1 Thecortex neostriatum thalamus corticalcircuitThesomaticmotorandsensoryareasinthecerebralcortex corticotriatumfibers neorstriatum striatopallidalfibers globuspallidus globuspallidothalamusfibers ventralanteriornucleusandventrallateralnucleus dorsalthalamus internalcapsule thesomaticmotorareainthecerebralcortex 2 Theneostriatum substantianigracircuitThecaudatenucleusandputamen substantianigra caudatenucleusandputamen RecentresearchesindicatethatthecauseofParkinsonismisdegenerationofthesubstantianigraandreductionofdopamineinthecorpusstriatum LesionsofthesubstantianigraandglobuspalliduscauseParkinsonismwhichmanifestsmuscularstiffnessandacoarsetremor especiallyinvolvingthemoredistalextremities 3 Thecortex pons cerebellum cortica
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