thalamus

Tissuemorphology

Thethalamusisdividedintothreemajornucleigroups,anterior,medial,andlateralbyaY-shapedwhitematterplate(calledtheinnermedullaryplate).Thenucleusofthethalamusanditsfiberconnection:

Prethalamicnucleus:Locatedinthedeepsideoftheanteriorthalamicnodule,itreceivesthenipple-thalamictractfromthepapillarybodyandemitsfiberstoprojecttothecingulategyrus.

Themedialthalamicnucleus:receivesfibersfromothernucleiofthethalamus,andemitsfibersthatprojecttothefrontalcortex.

Thelateralthalamicnucleus:itisdividedintoasmallerdorsalpartandalargerventralpart.Thedorsalpartreceivesothernucleusfibersofthethalamusandsendsoutfiberstotheparietalcortex.Theventralparthasextensiveconnectionswiththespinalcord,brainstem,andcerebellum.

Specificstructure

Bottom

Thebottomofthethalamusisthetransitionareabetweenthemidbraintegmentandthedorsalthalamus,includingthesubthalamicnucleusandForel'sarea.Thefibersthatreceivetheglobuspallidusandthemotorareaof​​thecortexsendfiberstotherednucleus,substantianigra,andthecoverofthemidbrain.

Back

Theposteriorpartofthethalamus:locatedbelowtheposteriorlateralpartofthethalamus,includingthemedialgeniculatebody,lateralgeniculatebody,andthalamusocciput.Themedialgeniculatebodyreceivestheauditoryfibersofthelateralcolliculussystem,andemitsfiberstoformauditoryradiation,whichisprojectedtotheauditoryareaof​​thetemporalcortex.Thelateralgeniculatebodyreceivesthefibersoftheopticbundleandemitsfibercalledopticradiation,whichisprojectedtotheoccipitalcortex.Thedeepsideofthethalamusocciputistheoccipitalnucleus,whichreceivesfibersfromtheinnerandoutergeniculatenucleiandsendsfiberstothecortexoftheinferiorparietallobule,occipitallobe,andposteriortemporallobe.

Upperpart

Theupperpartofthethalamus:locatedaroundthetopofthethirdventricle.Itincludestheleftandrighttriangles,thecommissure,andthepinealglandbehind.Thethalamicmedullastriaeoriginatingfromtheolfactorycenterendsinthetriangulargraymatter,andthefibersaresentfromthegraymattertothevisceralmotornucleusofthebrainstem.Therefore,theupperpartofthethalamusisrelatedtotheolfactoryvisceralreflex.

Lowerpart

Thelowerpartofthethalamus:Therearetwocharacteristics:oneisthattherearenotmanynervecells,buttheconnectioniscomplexandextensive;theotheristhatexceptforgeneralneurons,Italsocontainsendocrineneurons,whichhavethecharacteristicsofordinaryneuronsandhavethefunctionofsynthesizinghormonesbyendocrinecells.Thevolumeofthehypothalamusissmall,butitcontrolsmanyimportantfunctionsofthebody.Suchaswatermetabolism,bodytemperatureregulation,sugarmetabolism,fatmetabolism.

Nucleusclassification

Accordingtotheneuralconnection,thethalamusnucleusisroughlydividedinto3types

1.Thefirsttype(sensoryreplacementnucleus)istoacceptsensationProjectionfibers,andthosecellgroupsthatarefurtherprojectedtothesensoryareaof​​thecerebralcortex,suchasthelateralandmedialpartsoftheposteriorventralnucleus(calledtheposterolateralventralnucleusandthemedialventralnucleus,respectively),medialgeniculatebody,andlateralgeniculate体等。Bodyandsoon.Theposterolateralventralnucleusistheconversionstationofthespinothalamictractandthemedialthalamus,whichisrelatedtotheconductionoftrunkandlimbsensation;theposteromedialventralnucleusistheconversionstationofthetrigeminalcolliculus,whichisrelatedtotheconductionoftheheadandfacesensation.Thefibersfromtheposteriorabdominalnucleusprojecttothesensoryareaof​​thecerebralcortex.Thefibersfromdifferentpartsaredistributedintheposteriorabdominalnucleus.Thelowerlimbsarefeltontheoutermostpartoftheposteriorabdominalnucleus,andtheheadandfacearefeltontheinnersideoftheposteriorabdominalnucleus.,Andtheupperlimbsfeelinthemiddlepart(Figure10-22);thisspatialdistributioncorrespondstothespatialpositioningofthecerebralcortexsensoryarea.Themedialgeniculatebodyistheswitchingstationoftheauditorypathway,whichemitsfiberstoprojecttotheauditoryareaof​​thecerebralcortex.Thelateralgeniculatebodyistheswitchingstationofthevisualconductionpathway,whichemitsfiberstoprojecttothevisualareaof​​thecerebralcortex.Therefore,theabove-mentionedcellgroupisthereplacementsiteofallspecificsensoryimpulses(exceptsmell)transmittedtothecerebralcortex,calledthesensoryrelaynucleus.

Figure10-22Projectionofmonkeybodysurfaceontheposteriorventralnucleusoftheleftthalamus(posterolateralventralnucleusandposteromedialventralnucleus)

2.Thesecondtype(connectingnucleus)Receivefibersfromthefirsttypeofnucleusandothersubcorticalcenters(butnotdirectlyreceivesensoryprojectionfibers),andaftertransposition,theemittedfibersareprojectedtoaspecificareaof​​thecerebralcortex.Forexample,theanteriorthalamicnucleusreceivesfibersfromthepapillarybodyofthehypothalamus,andemitsfibersthatprojecttothecingulategyrusofthecerebralcortex,whichparticipatesintheregulationofvisceralactivity;thelateralventralnucleusofthethalamusmainlyreceivesfibersfromthecerebellum,globuspallidus,andposteriorventralnucleus.Emittingfibersprojecttothemotorareaof​​thecerebralcortexandparticipateintheregulationofmusclemovementbythecortex;thethalamusocciputreceivesfibersfromthemedialandlateralgeniculatebodies,andemitsfibersprojecttotheparietal,occipital,andtemporallobesofthecerebralcortex.,Participateintheconnectionfunctionofvarioussenses.Inaddition,therearemanycellgroupsinthethalamus,whichemitfibersthatprojecttothehypothalamus,theprefrontalandorbitalareasofthecerebralcortex,ortheheadquarterscontactareabehindtheparietallobe.Thesecellgroupsprojectedtothecontactareaof​​thecerebralcortex,whichisfunctionallyrelatedtothecoordinationofvarioussensationsatthelevelofthethalamusandcerebralcortex,collectivelyreferredtoasthecontactnucleus.

3.Thethirdtype(mainlythemedullaryplateinnercoregroup)isthevariousstructureswithintheso-calledinnermedullaryplatenearthemidline,mainlythemedullaryplateinnercoregroup,includingthecentralcentralnucleus,parafascicularnucleus,andcentralLateralnucleusandsoon.Itisgenerallybelievedthatthistypeofcellgroupdoesnotdirectlyprojecttothefibersofthecerebralcortex,butitisalsobelievedthatsomeofthenucleicanprojecttothemarginallobeandorbitalgyrus.Infact,thesecellpopulationscanindirectlyreplacethemeta-elementsthroughmultiplesynapses,andthendiffuselyprojecttotheentirecerebralcortex,playinganimportantroleinmaintainingtheexcitedstateofthecerebralcortex.Itisgenerallybelievedthatthediffuseprojectionofthesenucleigroupstothecerebralcortexisachievedindirectlythroughthereticularnucleusofthethalamus,butthespecificprojectionpathwaysarenotcompletelyclear.Studiesontheparafascicularnucleuspointoutthatitmayberelatedtopain;stimulationofthehumanthalamicparafascicularnucleuscanaggravatethepainsymptomsofpatients,anddamagetothisareacanrelievethepatient’spain;theelectrophysiologicalstudyoftheanimalparafascicularnucleushasobservedthatthenucleusThereareindeedcellsthataresensitivetonoxiousafferentimpulses.

Projectionsystem

Thethalamusistherelaystationforsensoryconduction.Exceptforsmell,theconductionpathwaysofvarioussensesreplaceneuronsinthethalamusandthenprojecttothecerebralcortex.Inthethalamus,onlytheroughanalysisandsynthesisofsensationsarecarriedout,andthefineanalysisandsynthesisofsensationsarecarriedoutinthecerebralcortex.

Accordingtothedifferentcharacteristicsoftheprojectionofvariouspartsofthethalamustothecerebralcortex,thethalamuscanbedividedintotwomajorsystems,oneisthespecificprojectionsystem,andtheotheristhenon-specificprojectionsystem(orcalledthediffuseprojectionsystem).

Specificprojectionsystem

Afterenteringthecentralnervoussystem,nerveimpulsesfromvariousreceptorsinthebodyareconcentratedtoreachthethalamusthroughafixedsensorypathway.Certainnervenuclei(exceptthesenseofsmell),whichemitfibersprojectedtothevarioussensoryareasofthecerebralcortex,producespecificsensations.Thisconductionsystemiscalledaspecificprojectionsystem.

Thetypicalsensorypathwayisgenerallycompletedbythereplacementoftertiaryneurons.Thefirst-levelneuronsarelocatedinthespinalgangliaorrelatedcranialnervesensoryganglia;thesecond-levelneuronsarelocatedinthedorsalhornofthespinalcordortherelevantnucleusofthebrainstem;thethird-levelneuronsarelocatedintheventro-posterolateralnucleusofthethalamus)-.However,thetransmissionpathwaysofspecialsensations(vision,hearing,smell)aremorecomplicated.Therefore,thethalamusisanimportantrelaystationofthespecificconductionsystem.Itcollectsvariousafferentimpulses(exceptsmell),andmakespreliminaryanalysisandsynthesistoproducearoughfeeling.However,thenatureandintensityofthestimulusareCannotperformpreciseanalysis.

ps:Thevisualtransmissionpathway,includingrodsandcones,isreplacedbyfourneurons.Theauditorypathwayfromtheperipherytothecerebralcortex,itisdifficulttobesurethatitwillbereplacedbyseveralneurons.Thesesensationsareprojectedtospecificsensoryareasinthecerebralcortexafterneuronreplacementinthelateralnucleusofthethalamus,lateralgeniculatebody,andmedialgeniculatebody,producingspecificsensations.

1. Specificprojectionsystemreferstothefiberconnectionofthelateralnucleus,lateralgeniculatebody,andmedialgeniculatebodyofthethalamustothecerebralcortex.Theclassicsensorypathwayactsonthecerebralcortexthroughthespecificprojectionsystemofthethalamus.Fromthethalamustothespecificareaof​​thecerebralcortex,thereisapoint-to-pointprojectionrelationship,andeachsensorytransmissionhasitsownspecificway.

Thefirsttypeofcellgroup,theyprojecttoaspecificareaof​​thecerebralcortex,withapoint-to-pointprojectionrelationship.

Mostofthesecondtypeofcellgroupalsohasaspecificprojectionrelationshipwiththecerebralcortexinstructure,andprojectstoaspecificareaof​​thecortex,soitcanalsobeattributedtoaspecificprojectionsystem.

Non-specific

Unspecificprojectionsystem.Whensensoryconductionprojectstothecerebralcortex,thatis,whenthefibersofthesecond-levelneuronsofthespecificprojectionsystempassthroughthebrainstem,theysendoutcollateralbranchestosynapsewiththeneuronsofthebrainstemnetworkstructure,andthenpassthroughthenetworkstructureTheshortaxonschangemultipletimesandprojecttoawideareaof​​thecerebralcortex.Thisprojectionsystemisacommonwayforwardfordifferentsenses.Aftervarioussensoryimpulsesenterthebrainstemnetworkstructure,aftermanyintricatelyintertwinedneuronsinteractwitheachother,theylosethespecificityofvarioussensations,andthereforeprojectedtothecerebralcortexnolongerproducespecificsensations.Therefore,thisconductionsystemiscalledanon-specificprojectionsystem.Thefirstfunctionofthissystemistostimulatetheexcitatoryactivityofthecerebralcortexandmakethebodyinastateofwakefulness.Therefore,thenon-specificprojectionsystemisalsocalledtheascendingactivatingsystem.Whentheafferentimpulseofthissystemincreases,theexcitatoryactivityofthecortexincreases,sothattheanimalstaysawake,andevencausesagitation;whentheafferentimpulseofthissystemdecreases,thecorticalexcitatoryactivityweakens,leavingtheanimalinarelativelyquietstate.State,evenalargeareaof​​thecortexturnsintoaninhibitedstateandcausessleep.Thesecondistoadjusttheexcitabilityofeachsensoryareaof​​thecortex,soastoincreaseordecreasethesensitivityofvariousspecificsensations.Ifthissystemisdamaged,theexcitementofthecortexisweakened,andtheanimalwillfallintolethargy.Sincethissystemisaforwardsystemwithmultiplesynapses,itissusceptibletoconductiondisordersduetotheactionofanesthetics.Someanesthetics,suchasDongmianling,actonthebrainstemnetworkstructure,blockthispathway,reducetheexcitabilityofthecortex,andcausequietnessandsleep.

Toproducesensationinthecerebralcortex,itdependsonthecooperationofspecificandnon-specificprojectionsystems.Onlythroughtheimpulseofthenon-specificprojectionsystemcanthesensoryareaof​​thecerebralcortexmaintainacertainexcitability.Atthesametime,onlythroughthevarioussensoryimpulsesofthespecificprojectionsystemcanaspecificsensationbeproducedinthecerebralcortex.

1. Thenon-specificprojectionsystemreferstothefiberconnectionsthatdiffuselyprojectfromthemedialnucleusofthethalamustoawideareaof​​thecerebralcortex.

2. Theaxonofthesecond-levelneuronoftheabove-mentionedclassicsensorypathway,whenpassingthroughthebrainstemonthewayup,sendsoutthesidebranchandthebrainstemnetworkstructureofneurongenerationSynapticconnection;thenrepeatedlychangeupinthenetworkstructure,reachthenucleusgroupinthemedialpartofthethalamus,andfinallydiffuselyprojecttoawideareaof​​thecerebralcortex.Experimentshaveshownthatstimulatingthemidbrainreticularstructurecanawakensleepinganimals;whilecuttingoffthereticularstructureattheheadofthemidbrain,theanimalcanbeinasleep-likestate.Ithasbeenobservedclinicallythatpatientswithdamagetothemidbrainreticularstructurearealsoinastateoflethargy.Itcanbeseenthatthereisafunctionalsystemthathasanupwardarousaleffectonthecerebralcortexinthebrainstemnetworkstructure,whichiscalledthebrainstemnetworkstructureupwardactivationsystem.Theascendingactivationsystemofthebrainstemreticularstructuremainlyworksthroughthenon-specificprojectionsystemofthethalamus.

Thenon-specificprojectionsystemreferstothethirdtypeofcellgroup,whichdiffuselyprojecttoawideareaof​​thecerebralcortex,anddoesnothaveapoint-to-pointprojectionrelationship

BrainstemReticulum

Theascendingreticulumactivationsystemandthethalamicnon-specificprojectionsystemarefunctionallyinseparableandformaunifiedsystem.Theyarethecommonpathwaysforvarioussensoryafferents.TheirroleisMaintainandimprovetheexcitementofthecerebralcortex.Therefore,sometimesthebrainstemnetworkstructureascendingactivationsystem-thalamusnon-specificprojectionsystemiscalledsensoryafferentnon-specificprojectionsystem.

Thesensoryafferentnon-specificprojectionsystemplaysanimportantroleinmaintainingthearousalstateofthecerebralcortex.Themorevariousafferentimpulses,themoreimpulsesthatenterthebrainstemnetworkthroughthecollateralbranches,andthusthestrongertheupwardarousaleffectonthecerebralcortex,thebetterthecortex'sexcitementstate,andthesensationofuploadingtothespecificprojectionsystemThemoreperfectitis.Therefore,thespecificprojectionsystemandthenon-specificprojectionsystemofsensoryafferentfunctionaremutuallydependentandindivisible.

Theascendingreticulumactivationsystemofthebrainstemnetwork-thalamicnon-specificprojectionsystemisanascendingsystemwithmultiplesynapses,soitissusceptibletotheinfluenceofdrugstocauseconductionblock.Forexample,barbituratesmayhavehypnoticeffectsbecausetheyblocktheconductionoftheascendingagonistsystem;somegeneralanesthetics(suchasether)alsofirstinhibittheascendingagonistsystemandtheactivityofthecerebralcortextoexertananestheticeffect.