thalamus | Definition, Anatomy, Function, & Disorders

thalamus, plural thalami, either of a pair of large ovoid organs that form most of the lateral walls of the third ventricle of the brain. thalamus TableofContents thalamus IntroductionDevelopmentofthethalamusThalamicnucleiRelaynucleiAssociationnucleiMidline/intralaminarnucleiReticularnucleusMedicalsignificance FastFacts Facts&RelatedContent Media Videos Images More MoreArticlesOnThisTopic Contributors ArticleHistory Home Health&Medicine Anatomy&Physiology thalamus anatomy Actions Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/thalamus GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites FactMonster-Science-Thalamus Alternatetitles:thalami By HalBlumenfeld SeeAll • EditHistory TableofContents structuresofthehumanbrain Seeallmedia RelatedTopics: subthalamicnucleus anteriornucleargroup ventrobasalcomplex diffusethalamicprojectionsystem subthalamus ...(Showmore) Seeallrelatedcontent→ thalamus,pluralthalami,eitherofapairoflargeovoidorgansthatformmostofthelateralwallsofthethirdventricleofthebrain.Thethalamustranslatesneuralimpulsesfromvariousreceptorstothecerebralcortex.Whilethethalamusisclassicallyknownforitsrolesasasensoryrelayinvisual,auditory,somatosensory,andgustatorysystems,italsohassignificantrolesinmotoractivity,emotion,memory,arousal,andothersensorimotorassociationfunctions.Anatomically,thethalamusliesdeepwithinthebrain,adjacenttothemidlinethirdventricle.Thepairedthalami(oneperhemisphere)areconnectedbythemassaintermedia(interthalamicadhesion).Thearterialsupplytothethalamiispredominantlybybranchesoftheposteriorcerebralarteries,aswellasbytheposteriorcommunicatingartery. 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DevelopmentofthethalamusThethalamusisderivedfromtheembryonicdiencephalonandearlyindevelopmentbecomesdividedintotwoprogenitordomains,thecaudaldomainandtherostraldomain.Thepatterningofthesedomainsisdrivenbythemid-diencephalicorganizer(MDO),whichsetsagradientoftranscriptionfactorstoformdistinctthalamicregions.Differentialtranscriptionofgenesleadstoneuronaldifferentiation.Thecaudalprogenitordomainleadstothedevelopmentofexcitatoryglutamatergicneurons(thosethatmodulateglutamateandaspartatesignaling),whichcontributetotheformationofthefunctionallyandspatiallydistinctgroupsofneuronsknownasthethalamicnuclei.Therostralprogenitordomainleadstothedevelopmentofinhibitorygamma-aminobutyricacid(GABA)neuronsthatformthethalamicreticularnucleus.ThalamicnucleiThemajornucleiofthethalamusincludetherelaynuclei,associationnuclei,midline/intralaminarnuclei,andthereticularnucleus.Withtheexceptionofthereticularnucleus,thesenucleargroupsaredividedregionally(i.e.,anterior,medial,andlateral)bysheetsofmyelinatedneuralfibresknownastheinternalmedullarylamina.Thereticularnucleusisseparatedfromtheremainderofthethalamicnucleibytheexternalmedullarylamina.Whiletherearenumerousmorphologies(shapes)totheneuronsthatcomposethethalamicnuclei,thalamicneuronsusuallyeitherprojectwithinthethalamus(interneurons)orprojecttothecerebralcortex.Thephysiologyofthalamiccellsisuniqueinthattheyshoweitheratonicpattern(regularlyspaced,continuousactionpotentials)oraburstingpattern(intermittentgroupingsofactionpotentials,suchasdoubletsortriplets),dependingonphysiologicalstateandactivity.Ingeneral,theconnectionsbetweentheperiphery(i.e.,sensoryorgans)andthethalamusarecontralateral(communicatedwiththeoppositesideofthebody),whiletheconnectionsbetweenthethalamusandthecerebralcortexareipsilateral(onthesamesideofthebrain).Mostthalamicnucleiprojecttothecortex,andallthalamicnucleireceivestrongreciprocalconnectionsfromthecortexbacktothethalamus.Eachnucleusisdiscussedinthefollowingsectionsinrelationtoitsinputs(afferents)andoutputs(efferents)inthecontextofthefunctionofthethalamicnucleus.RelaynucleiTheinferolateralregionisthepredominantrelaystationformotorandsensoryinformationinthecentralnervoussystem.Itiscomposedofmotornuclei;theventralanterior(VA)nucleus(ventraloralis)andventrallateral(VL)nucleus(ventralintermediate);andthesomatosensorynuclei(ventralcaudalnuclei),ventralposteriormedial(VPM),andventralposteriorlateral(VPL)nuclei.TheVAnucleusisinvolvedininduction,execution,andcontrolofaspectsofvoluntarymovement.Itpredominantlyreceivestopographicallysegregatedinputfromthesubstantianigraparsreticulataandfromtheglobuspallidusparsinterna(GPi),bothofwhichareneuronclustersofthebasalganglia,locatedbeneaththecerebralcortex.TheoutputofVAnucleusistothepremotorcortex,thesupplementarymotorarea,andtheprimarymotorcortex.TheVLnucleusisinvolvedinbalanceandfinemotorcontrol,withclinicalsignificanceasatargetforthetreatmentofessentialtremor.VLnucleusreceivesafferentspredominantlyfromthecerebellum,againinasomatotopicorganization,withadditionalinputfromtherednucleusandvestibularnuclei.TheVLnucleusprojectstocorticalmotorareas.TheVPMnucleusisinvolvedinsomatosensationforthehead;assuch,itreceivesinputfromthetrigeminalnervecomplex(nucleiofcranialnerveV).Itprojectstothefaceandheadareasintheprimarysomatosensorycortex.AregionadjacenttotheVPMknownastheventralposteriorparvocellularpart(VPPC)isthoughttoconveygustatory(taste)sensation.TheVPPCreceivesfibresfromsecondarytastefibresandautonomicafferents(fromthecardiovascularandgastrointestinalsystems),withprojectionstothesensorycortexregionthatliesadjacenttotheareasrespresentingthetongue,theinsula,andtheamygdala.TheVPLnucleusisinvolvedinsomatosensationforthebody(trunkandextremities).Itreceivesinputfromthemediallemniscalpathway(signalinglighttouchandproprioception)andfromthespinothalamictract(signalingtemperatureandpainstimuli).Itprojectsinatopographicallyorganizedfashiontotheprimarysomatosensorycortex.Thegeniculatebodiesaresmallnucleiontheposteriorinferioraspectofthethalamusresponsibleforsensoryrelayofvisualandauditoryinformation.Thelateralgeniculatenucleus(LGN)relaysvisualinformation,includingrepresentationsoflocationinthevisualfieldandcolour.Itreceivesinputfromthecontralateral(oppositeside)visualfield,withcontributionsfrombothopticnerves.Itisorganizedintooculardominancelayersmaintainingretinotopy,therepresentationoftheinputeyeandlocationinthevisualfield.Theoutputofthethalamusisthewhitematterfibretractknownastheopticradiations,whichprojecttotheprimaryvisualcortex.Themedialgeniculatenucleus(MGN)relaysauditoryinformation.Itreceivesinputfromtheinferiorcolliculusaswellasfromtheauditorycortex.TheMGNissubdividedintothreeregions:ventral,dorsal,andmedial.Theventralregionrelaysfrequency,intensity,andlaterality,whilethemedialregionencodesrelativesoundproperties.Thedorsalregionrelaysinformationaboutcomplexsounds.TheMGNhasoutputreciprocallytotheauditorycortexandisorganizedinatonotopic(bysoundfrequency)fashion. 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