Introduction
Thecentralnervoussystem(CNS)isthemainpartofthenervoussystem,includingthespinalcordinthespinalcanalandthebraininthecranialcavity;itslocationisofteninanimalsThecentralaxisofthebodyiscomposedofobviousbrainganglia,nervecords,orbrainandspinalcord,andtheconnectionsbetweenthem.Inthecentralnervoussystem,alargenumberofnervecellsgathertogethertoformanetworkorcircuitorganically;itsmainfunctionistotransmit,storeandprocessinformation,producevariousmentalactivities,anddominateandcontrolallanimalbehaviors.
Composition
Thecentralnervoussystemofvertebrates:thevertebratebrainislocatedinthecranialcavity,andthespinalcordislocatedinthespinalcanal.Thecentralnervoussystemofvertebratesdevelopsfromtheneuraltubeonthedorsalsideofthebodyatembryonictime.Theheadendoftheneuraltubeevolvedintothebrain,andthetailendbecamethespinalcord.Theneuraltubecavitydevelopsintotheventricleinthebrainandthecentraltubeinthespinalcord.Thebrainisthreebrainsatthebeginning:forebrain,midbrain,andrhombohedralvesicles,andlaterevolvedintoteleencephalon,diencephalon,midbrain,cerebellum,ponsandmedullaoblongata.
Manynervefibersinthecentralnervoussystemofvertebratesaremyelinated.Whentheyaregatheredtogether,theylookwhitetothenakedeyeandarecalledwhitematter.Onthecontrary,thepartwherethenervecellbodiesareconcentratedisgraytothenakedeyeandconsistsofalargenumberofnervecellbodiesandalargenumberofsynapsesondendrites,calledgraymatter.Thecentralnervoussystemiscomposedofacollectionofnervecellbodieswiththesamefunction,andthegraymattermasseswithaclearrangearecallednervenuclei.Theneuralactivitiescarriedoutinthespinalcordaremainlyreflexiveactivitiescarriedoutbysegments;however,manyactivitiesofvertebratesareintegrated,whichdependsontheconnectionbetweenthebrainandthespinalcord.Therearemanynervefiberbundlesrunninglongitudinallyinthecentralnervoussystem.Therearealsomanycommissuralfibersbetweentheleftandrightsidesofthebrainandspinalcord,thethickestofwhichisthecorpuscallosumbetweenthetwohemispheresofthebrain.
Features
Thespinalcordstillretainstheoriginalneuraltubepattern,withgraymattersurroundingthecentraltubeandwhitemattersurroundingthesurfaceofthegraymatter.Thedorsalpartofthespinalcordisdevelopedfromthewingplateoftheneuraltubeduringtheembryonicperiod,andmainlyreceivesincominginformationfromthereceptors.Theventralpartisdevelopedfromthebaseplate,anditsfunctionismotility.Thepositionofthecranialnervenucleusofthebrainstemisbasicallysimilartothearrangementofthespinalcordaccordingtoitssensoryandmotorproperties.However,duetothechangesintheshapeoftheventricle,itisnotasobviousandneatasthespinalcord.Somenervenucleiinthebrainstemthatareneithersensorynormotor,suchasrednucleiandolivenuclei,arelocatedindifferentpartsofthebrainstem.Duetotheappearanceoftheventricleandnumerousnervebundlesandconductionbundles,thestructureofthebrainstemismuchmorecomplicatedthanthatofthespinalcord(seetable).Thegraymatterofthecerebrumandcerebellumaremainlydistributedinthesurfacelayer,calledthecerebralcortexandcerebellarcortex,respectively;whilethewhitematterisinthedeeplayer.
Structure
Spinalcord
Spinecord-thelow-levelpartofthecentralnervoussystem,locatedinthespinalcanal,thefrontendoftheforamenmagnumandThebrainisconnectedwithperipheralnerves.31pairsofspinalnervesaredistributedonbothsidesofit,withthebackendreachingthemiddleofthepelvis.
Spinalcordmembrane:Thespinalcordiscoveredwiththreelayersofconnectivetissuemembranes,calledthespinalmembrane,whicharespinalpiamater,spinalarachnoidmembrane,andspinalduramaterfromtheinsidetotheoutside.Thespinalarachnoidandsoftmembraneformaconsiderablespacecalledspinalsubarachnoidspace,whichisfilledwithcerebrospinalfluid.Anarrowsubduralspaceisformedbetweenthespinalduramaterandthearachnoid,filledwithlymph.
Shape:Theshapeisslightlyflattenedupanddown,theendiscalledthemedullarycone,andithastwoenlargedpartscalledcervicalenlargementandlumbarenlargement(pelvicnerve,tailnerve).Itformsahorsetailtogetherwiththemedullaryconeandterminalfilaments);
Viewedfromthecrosssection,thecenterisabutterfly-shapedgraymatter,andthesurroundingiscomposedofwhitematter.Thereisacentraltubeinthecenterofthegraymatter.Thepartofgraymatterprotrudingbackwardandoutwardistheposteriorhorn,whichisconnectedtotheposteriorrootofthespinalnerveandcontainsinterneurons;thepartprotrudingforwardistheanteriorhorn,whichcontainsmotorneurons,anditsfibersconstitutetheanteriorrootofthespinalnerve;thelateralhorncontainsVegetativeneuron.Whitematteriscomposedofnervefibers,whichcanbedividedintoanteriorcord,lateralcord,andposteriorcordaccordingtolocation,whichconnectthebrain,spinalcord,andvarioussegmentsofthespinalcordrespectively.
Thefunctionofthespinalcordhasthefollowingtwoaspects:
First,theconductionfunction,thedeepandsuperficialsensationsofthewholebody(exceptthehead)andmostThesensationoftheinternalorgansmustbetransmittedtothebrainthroughthewhitematterofthespinalcordtoproducesensation.Thebrain'sregulationofthemovementofthetrunk,thestriatedmusclesofthelimbs,andtheinnervationandregulationofsomeinternalorganscanalsobeachievedthroughtheconductionofthewhitematterofthespinalcord.Ifthespinalcordisinjured,itsuploadingandsendingfunctionswillbeimpaired,causingsensoryimpairmentandparalysis.
Second,reflexfunction,therearemanylow-levelreflexcentersinthegraymatterofthespinalcord,whichcancompletesomebasicreflexactivities;suchasmusclestretchreflexcenters,urinationanddefecationcenters,andlow-levelreflexcentersforsexualactivities,Plantarreflex,kneejumpreflexandvisceralreflexandotherbodyreflexes.
Undernormalcircumstances,thereflexactivitiesofthespinalcordarecarriedoutunderthecontroloftheadvancedcentralnervoussystem.Whenthespinalcordissuddenlytraversedandlosescontactwiththehigh-levelcenter,atemporaryspinalshockwilloccur.Spinalcordinjurycaninterruptacertainlevelofphysiologicalfunction.Duetoadvancesinmedicine,manypatientswithspinalcordinjuryhavebeenabletorecovertheirphysiologicalfunctions.
Brain
Thehumanbrainisaspongynervetissueweighingabout1,400gramscomposedofabout14billionbraincells.Thebrainisthemainpartofthecentralnervoussystem.Intermsofstructure,itisdividedintothreeparts:forebrain,midbrainandhindbrainaccordingtodifferentparts,eachwithdifferentfunctions.
1.Thehindbrainislocatedatthelowerpartofthebrain,whichincludesthreeparts:
⑴Theoblongata,locatedattheupperendofthespinalcord,isconnectedtothespinalcordandhasathintubeshape,aslargeasafinger.Themainfunctionoftheoblongataistocontrolbreathing,heartbeat,swallowinganddigestion.Aslightinjurycanbelife-threatening.
⑵Thepons,locatedabovethedilatation,isatubularbodycomposedofnervefibersthatislargerthanthedilatation.Theponsconnectstheprolongedbrainandthemidbrain,andifdamaged,itmaycausesleepdisorders.
(3)Thecerebellum,locatedbehindthepons,resemblestwoconnectedwrinkledhemispheres,anditsfunctionismainlytocontrolthebody'smovementandbalance.Ifthecerebellumisdamaged,itlosestheabilityofthebodytomovefreely.
2.Themidbrainislocatedabovethepons,justinthemiddleofthewholebrain.Themidbrainisthereflexcenterofvisionandhearing.Inthecenterofthemidbrain,thereisanetworkofnervetissuecalledthereticularstructure.Themainfunctionofthemeshstructureistocontrolthestateofconsciousnesssuchasawakening,attention,andsleep.Theroleofthereticularstructureextendstothepons,midbrainandforebrain.Themidbrainandhindbrainponsandoblongataarecombinedtogether,calledthebrainstem,whichisthecenteroflife.
3.Theforebrainisthemostcomplexandimportantpartofthebrain.Theforebrainmainlyincludesfiveparts:
⑴Cerebralcortex,themostimportantpartofthecentralnervoussystem,withanaveragethicknessof2.5to3.0mm,anareaofabout2200squarecentimeters,coveredwithConcavegrooveandconvexback.Thedeepgroovethatseparatestheleftandrighthemispheresbecomesalongitudinalfissure.
Thebottomofthelongitudinalfissureisconnectedbythecorpuscallosum.Onthelateralsurfaceofthecerebralhemisphere,thesulcusperpendiculartothelongitudinalfissurefromthetopiscalledthecentralsulcus.Ontheoutersideofthehemisphere,thegroovethatrunsdiagonallyfromthefronttothebacktothetopiscalledthesylvianfissure.Theposteriorpartofthemedialhemispherehasparietooccipitalcleft.Beforethecentralgrooveisthefrontallobe.Theparietallobeisbehindthecentralgroove,infrontoftheparieto-occipitalfissure,andabovethelateralfissure.Belowthesylvianfissureisthetemporallobe.Theoccipitallobeisbehindthelateralfissure.Therearemarginalleavesaroundthecorpuscallosum.Eachleafcontainsmanytimes.Thereisacentralanteriorgyrusinfrontofthecentralsulcusandacentralposteriorgyrusbehind.Thedeeppartofthecerebralhemisphereisthebasalganglia,whichmainlyincludesthecaudatenucleusandthelenticularnucleus,collectivelycalledthestriatum.Itsfunctionismainlytoregulatemuscletensiontocoordinatemovement.
⑵Thelimbicsystem,thelimbicsystemisacomplexnervoussystemthatislocatedunderthecorpuscallosumandincludesavarietyofnervetissues.Thestructureandfunctionofthelimbicsystemarestilluncertain.Inadditiontopartofthethalamusandhypothalamus,italsoincludesthehippocampusandamygdala.Thefunctionofthehippocampusisrelatedtolearningandmemory,andthefunctionoftheamygdalaisrelatedtomotivationandemotion.
(3)Thethalamusisanegg-shapednervetissue,whichislocatedbelowthecorpuscallosumandfunctionsasatransferstation.Nerveimpulsesfromthespinalcordarefirststoppedinthethalamus,andthentransmittedfromthethalamustotherelevantareasofthecerebralcortex.Ifthethalamusisdamaged,itwilldistortthesensesandmakeitimpossibletocorrectlyunderstandtheworldaroundthem.
⑷Thehypothalamusislocatedbelowthethalamus.Althoughitsvolumeissmallerthanthatofthethalamus,itsfunctionismorecomplicatedthanthatofthethalamus.Thehypothalamusisthemaincontrolcenteroftheautonomicnervoussystem.Itisdirectlyconnectedtothevariousareasofthecerebralcortexandtothepituitaryglandwhichcontrolstheendocrinesystem.Themainfunctionofthehypothalamusistocontroltheendocrinesystem,maintainmetabolism,regulatebodytemperature,andisrelatedtohunger,thirst,sexandotherphysiologicalmotivationsandemotions.Damagetothehypothalamuswillaffecttheindividual'seatinghabitsandexcretoryfunction.
⑸Thepituitaryglandislocatedunderthehypothalamusandisaslargeasapea.Althoughitbelongstotheforebrainintermsoflocation,itisoneofthemostimportantsecretoryglandsintheendocrinesysteminfunction.Inaddition,thecorpuscallosumconnectsthetwohemispheresofthebrain,allowingtheneuralnetworksofthetwohemispherestocommunicatewitheachother.
Thebrainisthehigh-levelpartofthecentralnervoussystem.Itislocatedinthecranialcavityandcontinueswiththespinalcordattheforamenmagnum.Thebraincanbedividedintofourparts,brainstem,diencephalon,cerebrumandcerebellum.
(1)Brainstem,whichisdividedintomedullaoblongata,pons,andmidbrainfrombacktofront.
Themedullaoblongata:Itistheendofthebrainstem,whichiswideinthefrontandnarrowintheback.Thereareconesandtrapezoidsontheventralsideofthemedullaoblongata.Thebacksideisdividedintoaclosedpartandanopenpart.
Pons:Locatedinthefrontofthemedullaoblongata,itcanbedividedintothebasepartandthecover.Thebasepartbulgeslaterally,andthetrigeminalnervepenetratesatbothends.
Midbrain:Locatedbetweentheponsandthediencephalon,thereisatubecalledthemidbrainaqueduct.Thebackendcommunicateswiththefourthventricle,andthefrontcommunicateswiththethirdventricle.Dividedintodorsalquadruplebody(topcover)andventralbrainfeet.
Rednucleus:Itisapairoflargeoval-shapedgraymatternuclei,whichcanbeseeninthecrosssectionoftheanteriorcolliculusinthefrontofthefootofthebrain.Itisanimportantconversionstationonthedownwardmovementtransmissionpath.
(2)Diencephalon,anterolaterallyconnectedtothebasalnucleusofthebrain,insideisthethirdventricle,whichsurroundsinaring,andismainlydividedintothethalamusandthehypothalamus.
Thalamus:Itoccupiesmostofthethalamus.Itisapairofovalgraymattermasses.3ventricle.
Hypothalamus:alsoknownasthehypothalamus,locatedbelowthethalamus,isthesubcorticalcenteroftheautonomicnervoussystem.Viewedfromtheundersideofthebrain,theopticnervesonbothsidesformtheopticchiasm,grayNodules(funnel),nipplebody.
(3)Brain:
Cerebralneocortex:distributedonthebackandfront,lateralandposteriorsides,itcanbedividedintothefrontallobeandtheoccipitallobe(visualArea),thetemporallobeonthelateralside(auditoryarea),andtheparietallobeonthedorsalside(generalsensoryarea).BasalgangliaTherearesomelargegraymatterclustersinthewhitematterinsidethebrain,calledthebasalgangliaorbasalnucleus.Theyarethesubcorticalmotorcenterandaremainlycomposedofthecaudatenucleusandthelenticularnucleus.
Theolfactorybrain:constitutestheundersideoftheterminalbrain,includingtheolfactorybulb,olfactorygyrus,olfactorytriangle,piriformlobe,hippocampalgyrus,hippocampusanddentategyrus.
Marginallobe:referstotheoppositecortexbetweenthetwohemispheresofthecerebralhemisphere,includingthecingulategyrus,corpuscallosum,etc.,whichperformthefunctionsofregulatinginternalorgansandreproductiveactivities.
Whitematter:Thewhitematterofthecerebralhemispherecontainsthefollowingthree-sacredfibers:commissuralfibers—connectingthecorticalfibersoftheleftandrightcerebralhemispherestoformthecorpuscallosum;connectingfibers—connectingthefibersbetweenthegyrusandlobesoftheipsilateralhemisphere.Projectionfiber-connectingtheupanddownfibersbetweenthecerebralcortexandotherpartsofthecenter.
Lateralventricle:Locatedinsidethecerebralhemisphere,thereisoneoneachside,calledthefirstandsecondventriclesrespectively,andcommunicateswiththethirdventriclethroughtheinterventricularforamen.
(4)Cerebellum:
Thecerebellumisslightlyspherical,locatedonthedorsalsideofthemedullaoblongataandpons.Therearetwoshallowgroovesonthedorsalsidethatdividethecerebellumintothreeparts:thecerebellarhemisphereandthevermisDepartment.
(5)Circulationofmeninges,ventricularsystemandcerebrospinalfluid:
Minges:Similartothespinalcord,therearethreelayersofmeningesontheoutsideofthebrain,fromtheinsidetotheoutsidearethesoftbrains.Membrane,cerebralarachnoidandduramaterformthesubarachnoidspaceandsubduralspacerespectively,butthereisnoepiduralspace.
Ventricularsystem:lateralventricles,thethirdventricleinthediencephalon,themidbrainaqueductinthemidbrain,thefourthventricleinthecerebellum,theponsandthemedulla,andthecentralcanalinthespinalcord.,Filledwithcerebrospinalfluid,togetherconstitutetheventricularsystem.
Cerebrospinalfluid:Itisaspecialfluidthatisproducedbythechoroidplexusofthelateralventricle,thethirdventricleandthefourthventricle.Itfillstheventricularsystemandthesubarachnoidspaceofthecerebrospinalcordinthelongitudinalfissureofthebrain.Flowintotheveintocompletethecirculationofcerebrospinalfluid.
Role
Thecentralnervoussystemisagroupofneuronsthatregulateaspecificphysiologicalfunction.Suchasrespiratorycenter,bodytemperatureregulationcenter,languagecenterandsoon.Usually,somesimplereflexcentersarenarrow,suchasthecenterofkneejumpreflexinthelumbarspinalcord,andthecenterofcornealreflexinthepons.However,thecenterthatregulatesacertaincomplexlifeactivityhasawiderange.Forexample,thecenterthatregulatesbreathingmovementisscatteredinthemedullaoblongata,pons,hypothalamus,andcerebralcortex.Themedullaoblongatarespiratorycenterisbasic,andtherestofthecentersatalllevelsaffectit.Themedullaryrespiratorycenterregulatesrespiratorymovement.Itcanbeseenthatthereflexcenterisnotjustalimitedisolatedareainthecentralnervoussystem.Evenifthereareintricateconnectionsbetweenneuronsinacertainnervecenteratthesamelevel,theyaffecteachotheranddeterminethefunctionalactivitystateofthiscenter.Theactivityofthenervecentercandirectlyactontheeffectorthroughthenervefiber,orindirectlyactontheeffectorthroughthehumoralpathway.Thishumoralpathwayreferstoendocrineregulation.Sincethenervecenterofvariousreflexeshasadefinitelocation,checkingtheperformanceofacertainreflexordirectlyobservingtheactivityofcertaineffectororganscaninferthechangesinthefunctionofthecentertodiagnosediseasesordeterminethecondition.Ifthecenterofthecornealreflexisinthepons,lightlytouchtheedgeofthecorneawithcottonwool.Thenormalresponseistoclosetheeyes.Ifthecornealreflexisdullordisappear,itmeanstheponsisinjuredorcoma;TheAchillestendonshouldnormallybeflexedtotheplantarsurface.IftheAchillestendonreflexisweakenedordisappeared,itindicatesthecorrespondingcentralinjury.
Thecentralnervoussystemislikeahugecontainerofinformationprocessor,theresultofprocessingcanappearreflexactivities,feelingormemory.Forexample,whenananimalencounterssomethingharmful,itwillevade,whichisareflexaction.Inthisreflexaction,theinformationcausedbythenoxiousstimulusistransmittedtothecenter,processedbythecenter,andthentransmittedthroughthemotornerves,causingmuscleactivity.Afterthecentralnervoussystemreceivesincominginformation,itcanbetransmittedtospecificpartsofthebraintoproducesensations.Thiscanbeclearlyreportedinhumansbasedonsubjectiveexperience.Animalsmayalsohavethesameorsimilar"feeling".Aftersomesensoryinformationisintroducedintothecentralnervoussystem,afterthelearningprocess,itcanalsoleavetracesinthecentralnervoussystemandbecomenewmemories.
Whenthecentralnervoussystemcompletestheabove-mentionedfunctionalactivities,ithasaveryimportantfeature,thatis,coordinationandintegration.Coordinationreferstotheprocessinwhichthevariousfunctionsoftheoverallfunctionarecombinedintoaharmoniousmovement.Integrationreferstotheprocessofturningasingle,partialactivityintoacompleteactivity.Here,theoutputisnolongerinaone-to-onerelationshipwiththeinput,itcanbemultipleinputs,transformedintoasingleoutput,orviceversa.Forexample,whentheleftlegisflexed,therightlegisgenerallystraightenedinordertosupporttheweight,whiletheleftlegflexormusclesarecontracted,buttheextensormusclesarerelaxed.Theseactivitiesallreflectthecoordinationandintegrationofthecentralnervoussystem.
Origin
Thereticularnervoussystemoriginatesfromtheneuroectodermandisdifferentiatedfromtheneuraltubeandtheneuralcrest.
Tissuedevelopment
1.Neuraltube:Atthebeginningofthethirdweekofhumanembryo,thenotochordinducestheectodermofthedorsalmidline,theneuroectodermformstheneuraltube,andtheanteriorpartoftheneuraltubeisenlarged.Itderivesintothebrain,thebacksegmentisthinner,anditderivesintothespinalcord.
2.Neuralcrest:Duringtheformationoftheneuraltube,someneuroectodermalcellsattheedgeoftheneuralfoldsinkwiththeformationoftheneuraltube,formingtwocellcordsontheoutsideoftheneuraltube,calledtheneuralcrest,Theneuralcrestdifferentiatesintoganglia,glialcellsandadrenalmedullachromaffincellsoftheperipheralnervoussystem.
3.Neuraltubeepithelialdevelopment:Theearlyneuralplateisasinglelayerofcolumnarepithelium,calledneuroepithelium.Whentheneuraltubeisformed,thetubewallbecomespseudostratifiedcolumnarepithelium.
⑴Earlystructure:innerlimitingmembrane:alayerofmembraneontheinnersurfaceoftheneuraltubelumen;neuroepithelialcells:pseudostratifiedcolumnarepithelialcells;outermembrane:thebasementmembraneoftheepithelium.
⑵Structuraldevelopment:Theoriginalneuroepithelialcellsoftheinnerlimitingmembraneceasetodifferentiateandbecomealayerofcuboidalorshortcolumnarcells,calledtheependymallayer.Mantlelayer:Neuroepithelialcellscontinuetodivideandproliferate,andsomecellsmigratetotheperipheryofneuroepithelialcellstobecomeneuroblasts.Afterthat,neuroepithelialcellsdifferentiateintoglialcellsandmigratetotheperipheryofneuroepithelialcells.Thus,anewcelllayerisformedbyneuroblastsandglialcellsontheperipheryoftheoriginalneuroepithelialcells,whichiscalledthemantlelayer.Marginallayer:Theneuroblastsofthemantlelayeraresphericalatfirst,andquicklygrowprotrusions.Theprotrusionsgraduallygrowandextendtotheouterperipheryofthemantlelayer,forminganewstructurecalledthemarginallayer.Withthedifferentiationofneuroblasts,theglialcellsinthemantlelayeralsodifferentiateintoastrocytesandoligodendrocytes,andsomecellsenterthemarginallayer.
4.Nervecellsdevelopintoneuronalcells,whicharepost-dividingcells,andgenerallynolongerdivideandproliferate.Atfirstitwasround,calledanon-polarneuroblast.Later,twoprotrusionsoccurredandbecamebipolarneuroblasts.Theprotrusionsonthesideofthebipolarneuroblastsfacingtheneuraltubecavitydegenerateanddisappear,becomingunipolarneuroblasts,extendingtotheedgeOneprotrusionofthelayergrowsrapidlytoformaprimitiveaxon,andanumberofshortprotrusionsareformedonthemedialendoftheunipolarneuroblast,whichbecomesprimitivedendrites,andthenbecomesamultipolarneuroblast,andeachpolarneuroblastfurthergrowsanddifferentiatesintoeachpolarnervecell.
5.Glialcelldevelopment.Glialcellsoccurlaterthannervecells.Glioblastsfirstdifferentiateintoprecursorcellsofvarioustypesofglialcells,namelyastrocytesandoligoblasts.Dendrocytes;astrocytesdifferentiateintoprotoplasmicandfibrousastrocytes;oligodendrocytesdifferentiateintooligodendrocytes;glialcellsalwaysmaintaintheabilitytodivideandproliferate.
Theoccurrenceofspinalcord
1.Histogenesis:thelowersegmentoftheneuraltubedifferentiatesintothespinalcord.Thespinalcordbasicallymaintainstheabove-mentionedfive-layerstructure:theinnerlimitingmembraneandtheependymallayerbecometheependymaThemantlelayerdifferentiatesintospinalcordgraymatter,themarginallayerdifferentiatesintowhitematterandoutermembrane,anditslumenevolvesintothecentralcanalofthespinalcord.
2.Thejacketlayerevolvesintotwoventralbacksidesoftheleftandrightbaseplates,thetopandbottomwallsoftheleftandrightwingsarethetopandbottomwallsofthetopandbottomsulcus,anteriormedianfissure,andposteriormedianseptum.
⑴Thetwosidewallsoftheneuraltubethickenedrapidlyduetotheproliferationofneuroblastsandglialcellsinthemantle,formingtheleftandrightbaseplatesontheventralpart.Thedorsalpartoftheanteriorhornofspinalcordgrayformstwoleftandrightwingplates,whichformtheposteriorhornofspinalgraymatter.Severalneuroblastsgatherbetweenthebaseplateandthewingplatetoformthelateralhornofspinalgraymatter.
⑵Thetopandbottomwallsoftheneuraltubearethinandnarrow,formingthetopandbottomplates,respectively.
(3)Duetothethickeningofthebaseplateandwingplate,therearetwolongitudinalgroovesontheinnersurfaceoftheneuraltube,calledboundarygrooves.
⑷Asthenumberofcellscontinuestoincrease,alongitudinalgrooveappearsbetweentheleftandrightsubstrates,whichiscalledanteriormedianfissure.Theleftandrightwingplatesenlargeandmovetowardtheinsideandhealatthemidline.Aseptumisformedatthehealingplace,calledtheposteriormedianseptum.
3.Spinalcorddevelopmentbeforethethirdmonthofembryo:thespinalcordisaslongasthespine,anditslowerendcanreachthecoccyxofthespine.Afterthethirdmonth:becausethespinegrowsfasterthanthespinalcord,thespinegraduallysurpassesthespinalcordtothetailTheendisextended,andthepositionofthespinalcordmovesrelativelyupward.Beforebirth:Thelowerendofthespinalcordisflushwiththethirdlumbarvertebrae,andonlytheterminalfilaments(whicharestretchedintoathreadofthespinalcord)areconnectedtothetailbone.Sincethespinalnervesdistributedinsegmentsareformedintheearlyembryonicstageandpassthroughtheintervertebralforamenofthecorrespondingsegment,whenthepositionofthespinalcordmovesrelativelyupward,thespinalnerverootsbelowthecervicalsegmentofthespinalcordbecomemoreandmoreobliquetothecaudalside,tothewaistThespinalnerverootsofthesacralandcaudalsegmentsdescendverticallyinthespinalcanal,formingacaudaequinatogetherwiththeterminalfilaments.
Theoccurrenceofthebrain
1.Earlybrainstructure.Atthe4thweekoftheembryo,theheadoftheneuraltubeformedthreeswellings,namely,theforebrainvesiclesandthemiddlebrainvesiclesfromfronttoback.Cerebralvesiclesandrhombohedralvesicles.
2.Whenthestructureevolvestothe5thweek,theheadendoftheforebrainvesicleexpandstobothsides,formingtwoleftandrightendbrains,whichlaterevolveintothetwohemispheresofthebrainandthetailendoftheforebrainvesicleisformedThemidbrainmidbrainvesicleevolvedintothemidbrainrhombohedralvesiclethatevolvedintothecephalichindbrainandthecaudalendofthebrain,thehindbrainevolvedintotheponsandthecerebellarendofthebrain,andtheinnercavityofthemedullaoblongatabecametheventricleandthemidbrainaqueduct.
3.Thedevelopmentofbrainwallstructure.Theevolutionofthebrainwallissimilartothatofthespinalcord.Duetothethickeningofthemantlelayer,thesidewallisdividedintoadorsalwingplateandaventralbaseplate.
⑴Mostofthesidewallsofthetelencephalonanddiencephalonformwingplates,andmostofthecellsinthebaseplateandthesmalltelecephalusmigratetotheoutersurface,formingasmallgroupofcellsinthecerebralcortex.Theformationofthemarginallayerofthenucleusdifferentiatesintothewhitematterofthebrain.
⑵Themantlecellsinthemidbrain,hindbrainandendbrainaggregateintocellclustersorcellcolumns,formingvariousnervenuclei.Thenervenucleiinthewingplatearemostlythenervesinthesensoryrelaynucleussubstrate.Mostofthecoresaresportscores.
(3)Thecerebellumisdevelopedbythesymmetricalthickeningofthedorsalpartsofthewingsonbothsidesofthehindbrain.
Diseases
Thecentralnervoussystemisaffectedbypathogenicfactors(especiallywhentheorganicdiseaseofthenervoussystemcannotbedetected),andthediseasewithmentalactivitydisorderasthemainmanifestationiscalledMentalillness.Asthesayinggoes,mentalillnessisoftenreferredtoas"neuropathy",butitisactuallyincorrect.However,neuropathyandpsychosiscanoftencoexist.Forexample,sporadicencephalitisoftenhaspsychiatricsymptomsasthefirstsymptom,andpatientswithparalyticdementiacanalsohaveneurologicalsymptomsatanearlystage.Someneurologicaldiseases,suchascerebrovasculardisease,epilepsy,encephalitis,meningitis,etc.arecommonclinically.Chronicdiseasesaccountforthemajorityofneuropathies,andtheyoftenlingeranddonotheal,whichhasagreatimpactontheworkandlifeofpatients,andthedisabilityrateisveryhigh.Neuropathycanbecausedbyavarietyofcauses.Manyneuropathiesareofunknownetiology,andmanyaregeneticdiseases.TheapplicationoftechnologiessuchasbrainCTscanandmagneticresonanceimagingenablesrapidandaccuratediagnosisofmanybrainandspinalcorddiseases.However,becausenervecellsarenoteasytoregenerateafterinjury,therearestillnoeffectivetreatmentsformanyneuropathies.
Poisoning
Includingmetalpoisoning,suchasleadpoisoningcancauseperipheralmotornervepalsy,lead-toxicencephalopathy,mercury,arsenic,andthalliumpoisoningalsoaffectthenervoussystem;organicpoisoning,suchasalcoholPoisoningandbarbituratepoisoningcaninhibitthecentralnervoussystem,organophosphatepoisoningcancauseexcessiveexcitementofcholinergicnerves;bacterialtoxinpoisoning,suchasbotulismpoisoningcancausecranialnerveparalysisandlimbweakness,anddiphtheriatoxincancausenerveparalysisandtetanusToxinscancausetonicspasmsofskeletalmusclesthroughoutthebody;animalpoisons(toxinscontainedincoelenterates,shellfish,venomousmosquitoes,spiders,pufferfish,etc.)canalsocauseneurologicalsymptoms(muscleweakness,paralysis,convulsions,ataxia,etc.).
Viralinfections
Includingbacterialinfections,suchaspurulentmeningitisandbrainabscess,causedbyvariouspyogenicbacteria;viralinfections,suchasepidemicscausedbyJapaneseencephalitisvirusJapaneseencephalitis,epidemicchestpaincausedbyBMutantstrains;parasiticinfections,suchascerebralmalaria,cerebralparagonimiasis,cerebralcysticercosis;fungalinfections,suchasCandidaalbicansandcryptococcalmeningitis;Leptospiracanalsocausemeningitisencephalitis.Partofthecauseofepilepsyistheformationoflocalscarsaftermeningealorcerebralcortexinfection.
Centralnervoussystemvirusinfectionisoneofthemaincausesofchildren’snervoussysteminfectionanddeathallovertheworld.Althoughvaccinationcanpreventmanyseriousdiseasesofthenervoussystemcausedbyviruses(suchaspolio,measlesencephalitis,mumpsmeningoencephalitis,Japaneseencephalitis,etc.),therearestillmanyviralinfectionsthataffectthestructureandfunctionofthecentralnervoussystem.Causeseriousharm.Centralnervoussysteminfectionscausedbyvirusesincludeherpessimplexvirus(HSV)encephalitis,enterovirusinfection,congenitalcytomegalovirus(CMV)infection,humanimmunodeficiencyvirus(HIV)encephalopathy,andmanyothertypes.Theclinicalmanifestationsofcentralnervoussystemviralinfectionsarediverse,withacuteasepticmeningitisorencephalitisbeingthemostcommon.Therearestillsomedifficultiesinthediagnosisoftheetiologyofmostcases.Exceptforafewviruses,thetreatmentofcentralnervoussystemviralinfectionslacksspecificmethods.
Epidemiology
Centralnervoussysteminfectionscausedbycertainvirusesaffectpeopleofallages,withnoobviousseasonalorregionaldifferences,suchasherpessimplexViralencephalitis.However,someviraldiseaseshaveobviousepidemiccharacteristics.Forexample,arbovirusinfectionstendtooccurintheregionsandseasonswherethearboviruseslive.InChina,Japaneseencephalitismainlyoccursinsummerandautumn(JulytoSeptember),whichisrelatedtothebreedingseasonofitsmainmedia,Culexmosquitoes.Ithasbeenreportedthatabout70%ofviralencephalitisandmeningesoccurredfromJunetoNovember.About50%ofthecasesofviralencephalitisandmeningesoccurredinchildren,andboyswereslightlymoreaffected,withtheratioofmaletofemalebeing1.4:1.Theincidenceofencephalitisishighestinchildrenunder2yearsold,at16.7/100,000,andthelowestinadolescence(15yearsold),at1.0/100,000.Severaltypesofviralinfectionssuchasherpesvirus,enterovirus(exceptpoliovirus)andrespiratoryvirus(suchasadenovirus)accountforthemajorityofthisdisease.Thismayberelatedtomumps,rubella,measles,andpoliointhepastdecade.Itisrelatedtothewidespreadvaccinationoftheinflammatoryvirus.Before1960,mumpsandpoliovirusinfectionsaccountedforabout35%ofcentralnervoussystemvirusinfections.Incountrieswherethetwoviruseshavebeenimplemented,thenumberofpatientshasdecreasedsignificantly.In1992,only4casesofpoliowerereportednationwideintheUnitedStates.WiththeintensivevaccinationofpoliovirusvaccinesinChina,wildvirusinfectionshavebecomerelativelyrare.Thedevelopmentofotherpublichealthwork,suchasquarantine,mosquitocontrol,bloodproductmonitoring,andanimalvectorpreventiveimmunization,hasalsosignificantlyreducedmanytypesofnervoussystemvirusinfections.
Clinicalclassification
Accordingtothecharacteristicsoftheonsetandcourseofthedisease,viralinfectionsofthenervoussystemcangenerallybedividedintofourcategories:acute,subacute,chronicandembryonicencephalopathy.
Classificationofviruses
Accordingtobiologicalclassificationstandards,classificationshouldreflecttherelationshipbetweenorganismevolutionandphylogeny.Virusclassificationcannotyetbecarriedoutaccordingtothisprinciple.Therearemanyexistingclassificationmethods,andmostofthemaretheclassificationschemeproposedbytheInternationalCommissionforClassificationofViruses(ICTV).Firstlyaccordingtothetypeofnucleicacid,andthenfurtherclassificationaccordingtonucleicacidmolecularweight,structure,symmetrytypeofcapsid,numberofcapsid,envelopeandvirusmorphologyandsize.Scientistshavealsodiscoveredinfectiousagentsthataresmallerthanviruses,calledsubvims,includingviroid,vimsoidandvirino.PrionproteinorprionisaninfectiousproteinthatisresistanttonucleasefirstreportedbyAmericanscholarPrusinerin1982,alsoknownasproteininfector,whichisbelievedtocausemadcow(sheep)diseaseandhumanCJDandThecausativeagentofKurudisease.
Clinicalsymptoms
Manyvirusescancausenervoussysteminfection,butvariousvirusesmayhavedifferentpathogenicitytodifferentpartsofnervoustissue,soTheclinicalcharacteristicsaredifferent.PathologicalandpathophysiologicalcharacteristicsVirusinfectionsinhumansaremostlythroughtheskin,mucousmembranesorgastrointestinaltract,respiratorytract,andsomecasesareinfectedthroughiatrogenicroutessuchasbloodtransfusionandorgantransplantation.Aftertheinitialreplicationoftheinvasion,thehumanbloodisreleasedtoformviremia,andthenspreadtodistantorgans,especiallythereticuloendothelialsystem,resultinginsystemicsymptomssuchasfever,chills,abdominalpain,diarrhea,rash,orjointpain.Mostofthevirusesthatinvadethenervesenterthenervoussystemthroughthebloodduringthisperiod;afew,suchasrabiesviruses,invadethecentralnervoussystemthroughneuralpathways.Thepropagationofvirusesinnervecellscancausedamagetothecorrespondingcellfunctionsandstimulatethebody'simmuneresponse.Theinflammatoryresponseoflocaltissuestoviralinfectionsincludesanincreaseinlymphocytesandmacrophages,andanincreaseinneutrophilswilloccurifitundergoesanacutecourse.CytokinessuchasIL-1,IL-2,TNF-αandinterferonarealsoinvolvedintheinteractionbetweenthebodyandthevirus,andarerelatedtotheclinicalmanifestationsofinfectionandseriouscomplications.Inviralmeningitis,inflammatorycellsspreadtothepiamaterorsuperficialcortexthroughtheperivascularspace(Virchow--Robinspace),andthecorrespondingneuropathologicalchangesgenerallydisappearnaturallywithoutleavingsequelae.Butasmallnumberofcasescanoccurarachnoiditisorependymitis,blockingthecirculationofcerebrospinalfluidorcausingcerebrospinalfluidabsorptiondisorders,formingobstructiveorcommunicatinghydrocephalus.
Thetypicalneuropathologicalchangesofencephalitisincludepialmeningitis,perivascularleukocyteinfiltration,andmicrogliaproliferationtoformmicroglianodules.Thelocationandseverityoftheselesionsdependonthecharacteristicsofthehostandpathogenicfactors,andtheinfectionsofdifferentcasesanddifferentvirusesareverydifferent.Intheacutephase,thepathologicalchangesmaybemild,oronlymanifestedascerebraledema.Insevereorchronicencephalitis,severepathologicalchangesmayoccur,suchasneuronaldeath,tissuenecrosis,glialhyperplasia,andcysticencephalomalacia.Thepathologicalfeaturesofencephalomyelitisafterinfectionaremostlyedema,demyelinationaroundtheveinandinflammationofmononuclearcells.
Congenitalnervoussystemvirusinfection(alsoknownasintrauterineinfectionorembryonicencephalopathy)hasmanytypesofmanifestations,whichcanbemilddevelopmentalneurologicaldefectsorseverenecrotizingmeningesencephalitis.Neuropathologicalfeaturesinclude:①intracranialcalcification(rubellavirus,CMV,HSV,VZV,HIV,lymphocyticchoroidmeningitisvirus);②subependymalstromalcelllysis(rubellavirus,CMV);③nocerebralgyrus(CMV);④Periventricularwhitemattersoftening(CMV,Rubellavirus,HSV,HIV,VZV);⑤Hydrostaticanencephaly(HSV,CMV,VZV,Venezuelanequineencephalitisvirus);⑥Cysticencephalomalacia(HSV),CMV,VZV)etc.
Geneticdefect
Perhapsmetabolicdiseasesthataffectthenervoussystem(suchasphenylpropionicaciduria,glycogenstoragedisease,mucopolysaccharidosis,lipidstoragedisease),degenerativedisease(Suchasleukodystrophy,Parkinson'sdisease,amyotrophiclateralsclerosis,hereditaryopticatrophy,etc.)andmyopathy(suchasprogressivemusculardystrophy)aregeneticdiseases.Mostoftheinheritanceisautosomalrecessive.Theperiodicparalysisofhyperkalemiaandhypokalemiaisinheritedinanautosomaldominantmanner.
NutritionalDisorders
PatientswithKwahioko'sdisease(atypeofproteinthermalmalnutrition)mayhaveneurologicalsymptomssuchastremor,slowmovement,andmyoclonus.VitaminAdeficiencyorpoisoningcancauseintracranialhypertension.VitaminBdeficiencycanaffectthenervoussystem.Forexample,vitaminB1deficiency(beriberi)ismanifestedasmostperipheralnervedamage,andvitaminB12deficiencycancausesubacutecombineddegeneration.
CentralNervousSystemDiseasesCausedbyAlcohol
Wenike’sencephalopathy:Itisanacutedystrophicneurologicaldiseasecausedbylong-termalcoholism.Itcanalsooccurinothersituations,suchaschronicnutritionaldeficiencies,chronicwastingdiseases,andgastrointestinaldiseases.Mainlyduetothiamine(vitaminB1)deficiency.Thelesionsmainlyinvolvethethalamus,hypothalamus,papillarybodyandthethirdventricle,graymatteraroundthemidbrainaqueduct,andthebottomofthefourthventricleandthecerebellum.ThepathologicalchangesofacuteWynekencephalopathyaremainlyextensivespottinghemorrhageintheaboveparts,thatis,hemorrhage,necrosisandsofteningaroundthefourthventricleandsurroundinggraymatteroftheaqueduct,thalamusandotherparts,andlossofnervecellaxonandmyelinsheath.SubacuteWinnickencephalopathymayhavecapillaryincreaseandexpansion,cellproliferationandsmallhemorrhagicfoci,accompaniedbyneuronaldegenerationandmicroglialproliferation,andmacrophagereaction.ChronicWynnick'sencephalopathymayhaveatrophyofthepapillarybody,brownspongy,lossofparenchymalcomponentsinthelesionarea,activeastrocyteresponse,andoldsmallhemorrhagicfoci.
Alcoholictremor:oralcoholwithdrawaltremor,isthemostcommonmilderalcoholwithdrawalsyndrome.Itsoccurrenceisbelievedtoberelatedtotheexcessiveexcitementofcentralandperipheralnerveadrenergicreceptorsafteralcoholwithdrawal.Generally,theonsetis6-24hoursafterreducingalcoholconsumption.Tremorsoftenoccurinthemorning.Thefrequencyandintensityoftremorareirregular,andtheyweakenwhentheyarequiet,andaggravatewhenexerciseoremotionalstress.
Alcoholicepilepsy:alsoknownasrumseizures,referstothegeneralizedseizuresofseverealcoholismpatientswhodrinkalotofalcoholforacertainperiodoftimeafterasuddeninterruptionofdrinking.Itsoccurrencemayberelatedtothesharpchangeinbloodalcoholconcentrationafterweaning,whichcausedthedecreaseofserummagnesiumandpotassiumionconcentrationandtheincreaseofarterialbloodpH.Convulsionsusuallyoccurwithin48hoursafterabstinencefromalcohol.Iftheyoccurafter96hours,theyshouldbeconsideredasnon-abstinenceconvulsions.Theformofseizuresisgeneralizedtonic-clonicconvulsions,accompaniedbydisturbancesinconsciousness.Otherseizuresarealmostnon-existent,andseldomcontinuousseizures,withoccasionalstatusepilepticus.Thepatientmayhavewithdrawalsymptomssuchastremor,sweating,anddeliriumbeforetheattack,andtherearegenerallynofocalsymptomsandsignsatthetimeoftheattack.TheremaybetransientrhythmdisturbancesintheEEGduringtheactiveepilepticperiod,andtheremaybeparoxysmalsharpwavereleaseandslowerrhythm,butitcanquicklyreturntonormalwithinafewdaysafterstoppingdrinking.Deliriumtremor:referstoanacuteencephalopathysyndromethatoccursonthebasisofchronicalcoholism.Itmostlyoccursinalcohol-dependentpatientswhocontinuetodrinkalotofalcohol.Itcanbetriggeredbyfactorssuchastraumaandinfectionthatweakenthebody'sresistance.Itusuallyoccurssuddenly3to5daysaftergivingupdrinking,anditismainlymanifestedassevereconfusion,lossoforientation,vividdelusionsandhallucinations,accompaniedbytremor,anxiety,insomnia,andsympathetichyperactivity,suchasdilatedpupils,fever,Increasedbreathingandheartbeat,increasedordecreasedbloodpressure,andprofusesweating.Hallucinationsareoftenillusions,andthecontentismostlysmallanimals,suchassnakesandmice,andsomecanbequitevividandlifelike.
Alcoholicbrainatrophy:referstothereductionofbraintissuevolumeanddysfunctioncausedbychronicalcoholism.Itspathogenesisisunknown,anditmayberelatedtothedirectdamageofalcoholtothebrainandnutritionaldisorders,especiallythelackofvitaminB1.Itismorecommoninmiddle-agedandelderlymenwhodrinkalotofalcoholforalongtime.Theonsetishiddenandprogressesslowly.Anxiety,headaches,insomniaandfatiguearecommonintheearlystage,andtherearegraduallymentaldeclineandpersonalitychanges,whicharemanifestedbyobviouslossofmemory,declineincalculationability,judgmentandanalysisability,andafewcanhaveforgetting,fictionanddisorientation.Personalitychangescanincludeselfishness,undisciplinedlife,emotionalinstability,irritability,lowworkefficiency,lackofresponsibility,disobediencetoadvice,andtensionininterpersonalrelationships.Inaddition,somepatientsmayalsohaveperipheralneuropathy,muscleatrophy,andevenseverealcoholismsuchastremors,hallucinations,delusions,andseizures.HeadCTshowedsymmetricalenlargementofthelateralventricle,brainatrophy,suchaswideningofthesulci,interhemisphericfissure,andsylvianfissure.Alcoholiccerebellardegeneration:Referstothedegenerationofthecerebellarcortexcausedbylong-termheavydrinking.Themechanismisunclear,anditisthoughtthatitmayberelatedtoneurotrophicdisorders.Thelesionsaremainlyconfinedtothecerebellarvermis,andcanextendtotheanteriorlobeinthelaterstage.Mostpatientshavesubacuteorchroniconset.Therearesignificantlymorementhanwomen,andtheonsetoftenoccursaftermiddleage.Mainlymanifestedasataxiaofthelowerlimbsandtrunk,unsteadywalkingorclumsymovements,whilegaitandstandingareunusuallycommon.Inthebeginning,theturningisunstable,anditisdifficultorimpossibletowalkinastraightline.Gradually,thefeetwideninwalking,showingadrunkengait,hesitatingtowalk,anddifficultyinstanding.Therewasapositiveheelkneeshintestatthetimeofexamination.Theupperlimbsareoftenunaffected,andnystagmus,dysarthriaandhandtremorsarerare.Mostpatientsdevelopprogressively,andthenremainstaticformanyyears.Insomepatients,thecerebellarsymptomsdevelopinaleapingmanner,andthesymptomsoftenincreasesignificantlyafterinfection.Itcanbecombinedwithpolyneuropathy,roughtickdiseaseandbrainatrophy.CTorMRIalsohasatrophyofthecerebellarvermis.
Others
Theperipheralnervoussystem(Englishnameperipheralnervoussystem,PNSforshort)isthenervethatissentoutbythecentralnervoussystemandleadstovariouspartsofthehumanbody.Itisalsocalledtheperipheralnervoussystem(peripheralnervoussystem).):Accordingtothedifferentpartsconnectedtothecenter,itcanbedividedintothecranialnervesconnectedtothebrainandthespinalnervesconnectedtothespinalcord;itcanalsobedividedintothesomaticnervoussystemandthevisceralnervesaccordingtothedifferentdistributionobjects.Theperipheralnervoussystemisresponsibleforcommunicationwithallpartsofthebody,andplaystheroleofincomingandoutgoinginformation.