头晕相关脑解剖小脑.docx
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头晕相关脑解剖小脑
头晕相关的脑解剖
CerebellumAnatomyRelevanttoDizziness
TimothyC.Hain,MDMarcelloCherchi,M.D.,Ph.D.Pagelastmodified:
June14,2009
Thispageismeanttoprovideageneraloutlineofcerebellarfunction.ItisadaptedfromaclinicalneuroanatomylecturegivenonayearlybasistoNorthwesternPTstudents.Thispageis"underconstruction"andshouldnotbereliedupon.
Thecerebellumwithsurroundingskullandspinalfluidoccupiesthebottom1/3ofthisaxialMRIimage.
Whatisthecerebellumandwhatdoesitdo?
Thecerebellumispartofthebrain.Itliesunderthecerebrum,towardstheback,behindthebrainstemandabovethebrainstem.Thecerebellumislargelyinvolvedin"coordination".Personswhosecerebellumdoesn'tworkwellaregenerallyclumsyandunsteady.Theymaylookliketheyaredrunkevenwhentheyarenot.
GrossAnatomy:
CerebellarHemispheresandVermis
∙Cerebellarhemispheres,eachcontainingalateralandanintermediateportion
∙Vermis,situatedbetweenthetwocerebellarhemispheres;isbasicallycircular(interruptedbyfourthventricleventrally)
GrossAnatomy:
Lobes&Lobules
∙Anteriorlobe:
o1.Lingula
o2.Centrallobule
o3.Culmen
∙Posteriorlobe:
o4.Declive
o5.Folium
o6.Tuber
o7.Pyramis
o8.Uvula
o9.Tonsil
∙Flocculonodularlobe:
o(10.)Flocculus&nodulus
GrossAnatomy:
Fissures
∙Primaryfissure:
separatesanteriorandposteriorlobes
∙Horizontalfissure:
separatesposteriorlobe’srostrallobules(declive,folium)fromitscaudallobules(tuber,pyramis,uvula,tonsil)
∙Posterolateralfissure:
separatesposteriorandflocculonodularlobes
Connectionswithbrainstem:
∙Superiorcerebellarpeduncleconnectstomidbrain
∙Middlecerebellarpeduncleconnectstopons
∙Inferiorcerebellarpeduncleconnectstomedulla
SectionsoftheCerebellum
Vestibulocerebellumorarchicerebellum
∙Comprisestheflocculonodularlobe
∙Extensiveconnectionswiththevestibularsystem
∙Phylogeneticallyoldest
Spinocerebellumorpaleocerebellum
∙Comprisesthevermis(medial)¶vermal(intermediate)region
∙Extensiveconnectionswiththespinalcord&brainstem
∙Phylogeneticallyofintermediateage
Cerebrocerebellumorneocerebellum
∙Compriseslateralportionsofcerebellarhemispheres(excludingparavermalregions)
∙Extensiveconnectionswithcerebralcortexthroughrelaystationsincerebellarnucleianddorsalthalamus
∙Phylogeneticallyyoungest
CEREBELLARPEDUNCLES
Superiorcerebellarpeduncle(brachiumconjunctivum)
∙Connectstomidbrain
∙Afferents:
onlyventralspinocerebellartract
∙Efferents:
∙Mostoftheefferentsfromthecerebellum
∙Alloftheefferentsfromthree(outoffour)pairsofnuclei:
dentate,emboliform,andglobose
Middlecerebellarpeduncle(brachiumpontis)
∙Connectstopons
∙Afferents:
fromcerebralcortex(“corticoponto-cerebellarsystem”).
∙Corticopontineprojections(originatinginthecerebralcortex)synapseinipsilateralbasalpons. Fromthere,mostpontocerebellarprojectionsdecussate,passthroughmiddlecerebellarpeduncleandentercerebellum.
∙Asmallnumberremainipsilateral.
∙Efferents:
none.
Inferiorcerebellarpeduncle(“corpusrestiform”or“restiformbody”)
Connectstomedulla
∙Twocomponents:
∙Restiformbody
oAfferents:
▪Ascendingspinalproprioceptivefibersfromthreeofthespinocerebellartracts(dorsal,rostral,andcuneocerebellar)
▪Ascendingfibersfromcontralateralinferiorolivarynucleitocerebellarcortex(olivocerebellarprojections)
▪Reciprocalconnectionswithmotorreticularformationandspinocerebellum(paleocerebellum):
reticulocerebellarandcerebelloreticularprojections
∙Juxtarestiformbody
oMostlycontainsreciprocalconnectionstoandfromvestibulocerebellum(archicerebellum)andvermalportionofspinocerebellum(paleocerebellum):
vestibulocerebellarandcerebellovestibularfibers
CerebellarNuclei
Fastigialnucleus
∙Location:
Roofofthe4thventricle
∙Phylogeneticallyoldest
∙Associatedwiththevestibulocerebellum(archicerebellum)
∙Afferents:
oVestibulocerebellum
oVermis
∙Efferents:
oViainferiorcerebellarpeduncle
oTothevestibularnuclei
oSomeprojectdirectlytotheipsilateralside
oSomedecussate,looparoundsuperiorcerebellarpeduncleandreachthevestibularandreticularformationviatheuncinatebundleofRussell
Function:
∙Controlsantigravitymuscles
∙Controlsproximalmusclesofstance(station)&walking(ambulation)
Globoseandemboliform(the“interposednuclei”)
∙Location:
Roofofthe4thventricle,slightlylateraltothefastigialnuclei
∙Afferents:
Paravermianregionofspinocerebellum(paleocerbellum)
∙Efferents:
Viasuperiorcerebellarpeduncletocontralateralrednucleus
∙Function:
oMainlyinvolvedinmodulationofstretchreflexes
▪Distalmuscles
Dentatenucleus
∙Location:
Deepwithincerebellarwhitematter
∙Largestcerebellarnuclei
∙Afferents:
oPurkinjecellsofentirecerebrocerebellum(neocerebellum)andpartofspinocerebellum(paleocerebellum)
oPremotor&supplementarymotorcorticesviapontocerbellarsystem
∙Efferents:
oThroughsuperiorcerebellarpeduncle;crosstocontralateralrednucleus&thenonventrolateralnucleusofthalamus
∙Function:
oHelpstoinitiateandcontrolvolitionalmovements
Vestibularnucleus
∙“Displaced”cerebellarnuclei
∙Closelyassociatedwithvestibulocerebellum(archicerebellum)
∙Function:
∙Maintaingazefixation
∙Maintainuprightposture
CEREBELLARHistology:
CorticalLayers
∙Molecularlayer(outermostlayer)contains:
oCellbodies:
stellatecells,basketcells
oCellprocesses:
dendritesofthePurkinjecells,dendritesofGolgicells,axons(parallelfibers)ofgranulecells,axonsofstellatecells
oPurkinjelayer(middlelayer)contains:
oCellbodies:
onlyPurkinjecells
oCellprocesses:
dendritesofGolgicells,axonsofbasketcells
∙Granularcelllayer(innermostlayer)contains:
o1x1011neurons(moreneuronsthanentirecerebralcortex!
)
oCellbodies:
granulecells,Golgicells
oCellprocesses:
dendritesofGolgicells,axons(Purkinjecell,granulecell,Golgicell,climbingfibers,mossyfibers),glomeruli(bulbousexpansionsofmossyfiberswheresynapticcontactwithgranulecellsandGolgicellsismade
Histology:
CellTypes
∙Purkinje
∙Granule
∙Golgi(interneuron)
∙Basket(interneuron)
∙Stellate(interneuron)
PurkinjeCells
LargestcellsinCNS(cellbody=60-90µmindiameter)
Cellbody
∙InPurkinjecelllayer
∙Inhibitorysynapse(GABA)frombasketcells
∙Excitatorysynapse(aspartate)fromasingleclimbingfiber
Dendrite
∙Inmolecularlayer
∙Dendriticarboris“planar,”orientedinarostrocaudalplane
∙Inhibitorysynapses(GABA&taurine)fromstellatecells
∙Excitatorysynapses(glutamate)fromgranulecells’parallelfibers. Over200,000mossyfibersindirectly(throughGolgicell,thengranulecell)exciteeachPurkinjecell
Axon
∙Theonlyprojectionsthatexitthecerebellarcortex
∙Mostlyprojecttocerebellarnuclei(toallfour);somefibersprojecttovestibularnucleiinbrainstem
∙Formsinhibitorysynapses(GABA)
∙Oftenalsoreleasesapeptidecotransmitter
GranuleCells
1x1011granulecells(moreneuronsthanentirecerebralcortex!
)
Cellbody
∙Locatedingranulecelllayer
∙Inhibitorysynapse(GABA)fromGolgicells
Axon
∙Projectsfromgranulecelllayer,throughPurkinjecelllayer,uptomolecularlayer,whereitformsparallelfibers(whichareorientedinahorizontalplane,paralleltothecerebellarfolia)
∙Formsexcitatorysynapses(glutamate)onGolgi,basketandstellatecell
GolgiCells
∙Interneuron
∙Cellbodylocatedingranulecelllayer
∙Dendritesinallthreelayers,receivingexcitatorystimuli
∙Granulecells’parallelfibersformexcitatorysynapses(glutamate)inmolecularlayer
∙Climbingfibers(frominferiorolivarynucleus)formexcitatorysynapses(aspartate)inmolecularlayer
∙Mossyfibers
oformexcitatorysynapses(acetylcholine)ingranulecelllayer
oarrivefromspinocerebellarpathway,vestibularafferents,brainstemreticularformation,cerebropontocerebellarsystem’spontocerebellarprojections
oformthesinglelargestinputtocerebellum
oindirectlyexcitePurkinjecells(incontrasttoclimbingfibers,whichdirectlyexcitePurkinjecells)
oAxonsprojectswithinthegranulecelllayerontogranulecells,forminginhibitorysynapses(GABA),therebyactingasa“brake”totheexcitationofgranulecells;itcurtailsthedurationofexcitation
BasketCells
∙Interneuron
oCellbodylocatedinmolecularlayer
oNamederivesfromthefactthatitsaxonsform“basket-like”terminalarborsaroundsomaofPurkinjecells
∙Dendrites
oOrientedinrostrocaudalplane(perpendiculartofolia)
oReceiveexcitatorystimuli(glutamate)fromgranulecells’parallelfibers
∙Axons
oOrientedinrostrocaudalplane(perpendiculartofolia)
oProjectfrommolecularcelllayertoPurkinjecelllayer
oForminhibitorysynapses(GABA)withPurkinjecellbody
StellateCells
∙Interneuron
oCellbodylocatedinmolecularlayer
∙Dendrites
oOrientedinrostrocaudalplane(perpendiculartofolia)
oReceiveexcitatorystimuli(glutamate)fromgranulecells’parallelfibers
∙Axons
oProjectwithinthemolecularlayer
oForminhibitorysynapses(GABAandtaurine)onPurkinjecelldendrites
CerebellarCircuits
MossyFiberSystem
∙Largestinputtocerebellum(99%),mostofwhicharefromcerebropontocerebellarsystem(mostlyfrom1˚&2˚motorareasand1˚somatosensoryarea)
∙Formexcitatorysynapses(acetylcholine)
∙Severalaffer