LIMBICSYSTEMMENINGESOFTHEBRAIN

BASALGANGLIACNI

THELIMBICSYSTEM

Thelimbicsystemisresponsibleforcontrolofouremotionsandbehaviour,motivationandmemory,alsoaffectstheautonomicandsomaticnervoussystemaswellastheendocrinehypothalamus-hypophysealaxis.Thelimbicsystemisexpressedthroughthehypothalamusbywayoftheautonomicnervoussystem.

LIMBICSYSTEM

Aprominentstructureinthelimbicsystemisthehippocampalformationonthemedialaspectofthetemporallobe.Itconsistsofacoreofcorticalanddiencephalicstructuresfoundonthemedialaspectofthehemisphere.

Thehippocampalformationextendsalongtheflooroftheinferiorhornofthelateralventricleinthetemporallobeandincludesthehippocampus,thedentategyrus,thesubiculum,andadjacententorhinalcortex.Thehippocampusischaracterizedbya3-layeredcerebralcortex.

LIMBICSYSTEM

Otherlimbic-relatedstructuresincludetheamygdala,whichislocateddeepinthemedialpartoftheanteriortemporalloberostraltothehippocampus,andtheseptalnuclei,locatedmediallybetweentheanteriorhornsofthelateralventricle.

Thelimbicsystemisinterconnectedwiththalamicandhypothalamicstructures,includingtheanterioranddorsomedialnucleiofthethalamusandthemammillarybodiesofthehypothalamus.

LIMBICSYSTEM

Thecingulategyrusisthemainlimbiccorticalarea.Thecingulategyrusislocatedonthemedialsurfaceofeachhemisphereabovethecorpuscallosum.Limbic-relatedstructuresalsoprojecttowideareasoftheprefrontalcortex.

Thelimbicsystemisinvolvedinemotion,memory,attention,feeding,andmatingbehaviors.Thelimbicsystemmodulatesfeelings,suchasfear,anxiety,sadness,happiness,sexualpleasure,andfamiliarity.

LIMBICSYSTEM

Theterm‘limbicsystem’hasbecomepopulartodescribethelimbiclobealongwiththecloselyassociatedsubcorticalnuclei,includingtheamygdala,septum,hypothalamus,habenula,anteriorthalamicnucleiandpartsofthebasalganglia.

Thelimbicsystemconsistsof-  corticaland-  subcorticalstructures.Thecorticalstructuresarelocatedpredominantlyonthemedialaspectofthecerebralhemispheres.Thesubcorticalstructuresarelocatedinthebasalganglia,diencephaion,brainstem,andreticularformation.Thesestructuresarereciprocallyinterconnectedbyvariousneuralpathwaysandcircuits,andtheycontributetotheregulationofhomeostasis.

LIMBICSYSTEM

MAJORPARTSOFTHELIMBICSYSTEM:Theorbitofrontalcortexmediatestheconsciousperceptionofsmell.Ithasreciprocalconnectionswiththemediodorsalnucleusofthethalamus.Itisinterconnectedthroughthemedialforebrainbundlewiththeseptalareaandhypothalamicnuclei.Thedorsomedialmediodorsalnucleusofthethalamushasreciprocalconnectionswiththeorbitofrontalandprefrontalcorticesandthehypothalamus.Itreceivesinputfromtheamygdalaandplaysaroleinaffectivebehaviorandmemory.Theanteriornucleusofthethalamusreceivesinputfromthemamillarynucleusthroughthemamillothalamictractandfornix.ItprojectstothecingulategyrusandisamajorlinkinthePapezcircuit.

LIMBICSYSTEM

MAJORPARTSOFTHELIMBICSYSTEM:Theseptalareaisatelencephalicstructure.Ithasreciprocalconnectionswiththehippocampalformationthroughthefornixandwiththehypothalamusthroughthemedialforebrainbundle.Itprojectsthroughthestriamedullaris(thalami)tothehabenularnucleus.Thelimbiclobeincludesthesubcallosalarea,paraterminalgyrus,cingulategyrusandisthmus,andparahippocampalgyrus,whichincludestheuncus.Itcontains,buriedintheparahippocampalgyrus,thehippocampalformationandamygdaloidnuclearcomplex.

LIMBICSYSTEM

MAJORPARTSOFTHELIMBICSYSTEM:Thehippocampalformationisasheetofarchicortexthatisjelly-rolledintotheparahippocampalgyrus.Itfunctionsinlearning,memory,andrecognitionofnovelty.

LIMBICSYSTEM

Theamygdaloidcomplex(amygdala)isabasalnucleusthatunderliestheparahippocampaluncus.Inhumans,stimulationcausesfearandsignsofsympatheticoveractivity.Lesionscauseplacidityandhypersexualbehavior.Thehypothalamushasreciprocalconnectionswiththeamygdala.Thelimbicmidbrainnucleiandassociatedneurotransmittersincludetheventraltegmentalarea(dopamine),raphenuclei(serotonin),andlocusceruleus(norepinephrine).Thehippocampalformationreceivesmajorinputthroughtheentorhinalcortexandprojectsmajoroutputthroughthefornix.

Themajorstructuresofhippocampalformation:1.Thedentategyrus,whichhasathree-layeredarchicortex.Itcontainsgranulecellsthatreceivehippocampalinputandprojectoutputtothepyramidalcellsofthehippocampusandsubiculum.2.Thehippocampus(cornuAmmonis),whichhasathree-layeredarchicortex.Itcontainspyramidalcellsthatprojectthroughthefornixtotheseptalareaandhypothalamus.3.Thesubiculum,whichreceivesinputthroughthehippocampalpyramidalcells.Itprojectsthroughthefornixtothemamillarynucleiandtheanteriornucleusofthethalamus.

LIMBICSYSTEM

Theamygdaloidcomplex(amygdala)gets:1.Inputisfromthesensoryassociationcortices,olfactorybulbandcortex,hypothalamusandseptalarea,andhippocampalformation.2.Outputisthroughthestriaterminalistothehypothalamusandseptalarea.Thereisalsooutputtothedorsomedialnucleusofthethalamus.

LIMBICSYSTEM

Onthebasisofemotionaldisturbancesdisplayedbypatientswhopresentedwithdamagetothehippocampusandcingulategyrus,Papez(1937)describedaclosedcircuit(thePapezcircuit),whichlinkedthehippocampuswiththecingulatecortex,viathemammillarybodiesandanteriorthalamus.

LIMBICSYSTEM

AsummaryofthesimplifiedconnectionsofthelimbicsystemisexpressedbythePapezcircuit.

ThePapezcircuitoversimplifiestheroleofthelimbicsysteminmodulatingfeelings,suchasfear,anxiety,sadness,happiness,sexualpleasure,andfamiliarity.

Arbitrarily,thePapezcircuitbeginsandendsinthehippocampus.Axonsofhippocampalpyramidalcellsconvergetoformthefimbriaand,finally,thefornix.Thefornixprojectsmainlytothemammillarybodiesinthehypothalamus.

LIMBICSYSTEM

Themammillarybodies,inturn,projecttotheanteriornucleusofthethalamusbywayofthemammillothalamictract.Theanteriornucleiprojecttothecingulategyrusthroughtheanteriorlimboftheinternalcapsule,andthecingulategyruscommunicateswiththehippocampusthroughthecingulumandentorhinalcortex.

Theamygdalafunctionstoattachanemotionalsignificancetoastimulusandhelpsimprinttheemotionalresponseinmemory.

LIMBICSTRUCTURESANDFUNCTION•  Hippocampalformation(hippocampus,dentategyrus,the

subiculum,andentorhinalcortex)•  Amygdala•  Septalnuclei•  Thehippocampusisimportantinlearningandmemory.The

amygdalaattachesanemotionalsignificancetoastimulusandhelpsimprinttheemotionalresponseinmemory.

LIMBICSYSTEM

LIMBICCONNECTIONSThelimbicsystemisinterconnectedwithanterioranddorsomedialnucleiofthethalamusandthemammillarybodies.Thecingulategyrusisthemainlimbiccorticalarea.Limbic-relatedstructuresalsoprojecttowideareasoftheprefrontalcortex.Centralprojectionsofolfactorystructuresreachpartsofthetemporallobeandtheamygdala.

LIMBICSYSTEM

THEPAPEZCIRCUITincludesthefollowinglimbicstructures:•  hippocampalformation,whichprojectsthroughthefornixtothe

mamillarynucleusandseptalarea•  mamillarynucleus•  anteriorthalamicnucleus•  cingulategyrus(Brodmann’sareas23and24)•  entorhinalarea(Brodmann’sarea28)

LIMBICSYSTEM

THEPAPEZCIRCUIT:•  originatesinthehippocampus•  runsviathefornix•  entersthemammillarynucleiinthehypothalamus•  runsfurtherviathemammillothalamictract•  enterstheanteriorthalamicnucleus•  projectstothecingulategyrusandorbitofrontalassociationcortex•  runsviathecingulum(pathwaywithinthecingulategyrus)•  intotheentorhinalcortex•  thenthecircuitterminatesinthesubiculumandhippocampus

LIMBICSYSTEM

ANTEROGRADEAMNESIABilateraldamagetothemedialtemporallobesincludingthehippocampusresultsinaprofoundlossoftheabilitytoacquirenewinformation,knownasanterogradeamnesia.KORSAKOFFSYNDROMEAnterogradeamnesiaisalsoobservedinpatientswithKorsakoffsyndrome.KorsakoffsyndromeisseenmainlyinalcoholicswhohaveathiaminedeficiencyandoftenfollowsanacutepresentationofWernickeencephalopathy.Wernickeencephalopathypresentswithocularpalsies,confusion,andgaitataxiaandisalsorelatedtoathiaminedeficiency.InWernicke-Korsakoffsyndrome,lesionsarealwaysfoundinthemammillarybodiesandthedorsomedialnucleiofthethalamus.

LIMBICSYSTEM

THEMENINGESOFTHEBRAIN

Threeconcentricmembranes,theMENINGES,envelopthebrainandspinalcord.

MENINGES

Theyprovidesupportandprotectionforthedelicatetissuestheysurround.

The3individuallayers,inorderfromoutsidetoinside,aretheduramater,arachnoidmaterandpiamater.

DURAMATER(DURA):tough,thickfibrouscoatwhichincompletelydividesthecranialcavityintocompartmentsandaccommodatestheduralvenoussinuses.unlikethespinaldura,consistsof2layers(periostealandmeningeal)thatarefusedtogetherduringmostoftheircourseinthecranialcavity

MENINGES

DURAMATER(DURA)Periosteallayer:Thisouterlayerlinestheinnersurfacesoftheflatbonesandservesastheirperiosteum.Theperiosteallayercaneasilybepeeledawayfromthebones.Meningeal(truedura)layer:Thisistheinnermostlayerthatismostlyfusedwiththeperiostealduramaterthroughoutthecranialcavity.Meningeal(truedura)layer:Atcertainpointsinthecranium,themeningeallayerseparatesfromtheperiosteallayerandformstheduralvenoussinusesandconnectivetissuefoldingsorduplications:falxcerebri,diaphragmasellaeandtentoriumcerebelli.TheseduplicationsseparateandsupportdifferentpartsoftheCNS.

MENINGES

THECRANIALDURAMATER(DURA)Theduralinfoldingsdividethecranialcavityintocompartments,formingpartialpartitions(duralsepta)betweencertainpartsofthebrainandprovidingsupportforotherparts.

MENINGES

Theduralinfoldingsincludethe:•  Falxcerebri(cerebralfalx)•  Tentoriumcerebelli(cerebellartentorium)•  Falxcerebelli(cerebellarfalx)•  Diaphragmasellae(sellardiaphragm)

THECRANIALDURAMATER(DURA)Thefalxcerebriisthelargestduralinfolding,liesinthelongitudinalcerebralfissurethatseparatestherightandtheleftcerebralhemispheres.Thefalxcerebriattachesinthemedianplanetotheinternalsurfaceofthecalvaria,fromthefrontalcrestofthefrontalboneandcristagallioftheethmoidboneanteriorlytotheinternaloccipitalprotuberanceposteriorly.Thefalxcerebriendsbybecomingcontinuouswiththetentoriumcerebelli.

MENINGES

THECRANIALDURAMATER(DURA)Thetentoriumcerebelliisawidecrescenticseptumthatseparatestheoccipitallobesofthecerebralhemispheresfromthecerebellum.Thetentoriumcerebelliattachesrostrallytotheclinoidprocessesofthesphenoid,rostrolaterallytothepetrouspartofthetemporalbone,andposterolaterallytotheinternalsurfaceoftheoccipitalboneandpartoftheparietalbone.Thefalxcerebelliisaverticalduralinfoldingthatliesinferiortothetentoriumcerebelliintheposteriorpartoftheposteriorcranialfossaandpartiallyseparatesthecerebellarhemispheres.

MENINGES

THECRANIALDURAMATER(DURA)Thediaphragmasellaeissuspendedbetweentheclinoidprocessesformingapartialroofoverthehypophysialfossainthesphenoidandcoversthepituitaryglandinthisfossa.

MENINGES

ARACHNOIDMATER(ARACHNOID)Itismuchthinnerthantheduraandismostlytranslucent.Itsurroundsthebrainloosely,spanningoverdepressionsandconcavities.Projectionsofarachnoidcalledarachnoidgranulationspenetratethroughtheduramaterandextendintothesuperiorsagittalduralvenoussinus.ArachnoidgranulationsarewhereCSFreturnstothesystemicvenouscirculation.

MENINGES

PIAMATER(PIA)Delicateinternalvasculatedlayer,microscopicallythin,membranewhichfollowsthecontoursofthebrainandiscloselyadherenttoitssurface.Tightlyinveststhesurfacesofthebrainandcannotbedissectedaway,havingthesamerelationshipwiththebrainasspinalpiamater

MENINGES

THEMENINGES:1.Duramater(dura):tough,thickfibrouscoatwhichincompletelydividesthecranialcavityintocompartmentsandaccommodatestheduralvenoussinuses.2.Arachnoidmater(arachnoid):ismuchthinnerthantheduraandismostlytranslucent.Itsurroundsthebrainloosely,spanningoverdepressionsandconcavities.3.Piamater(pia):delicateinternalvasculatedlayer,microscopicallythin,membranewhichfollowsthecontoursofthebrainandiscloselyadherenttoitssurface.

MENINGES

THEARACHNOIDANDPIAMATERThearachnoidmaterandthepiamatertogetheraresometimesreferredtoastheleptomeninges.

Theduraisseparatedfromthearachnoidbyanarrowsubduralspace.

MENINGES

Thearachnoidisseparatedfromthepiabythesubarachnoidspace,whichvariesgreatlyindepth;thelargerexpansesaretermedsubarachnoidcisterns,whichcontainscerebrospinalfluid(CSF).

Theduraisseparatedfromthearachnoidbyanarrowsubduralspace.Thearachnoidisseparatedfromthepiabythesubarachnoidspace,whichvariesgreatlyindepth;thelargerexpansesaretermedsubarachnoidcisterns,whichcontainscerebrospinalfluid(CSF).

Thecerebrospinalfluid(CSF)isformedbythechoroidplexusesofthefourventriclesofthebrain.

MENINGES

Thecerebrospinalfluid(CSF)leavestheventricularsystemandentersthesubarachnoidspacebetweenthearachnoidandpiamater.

SPACESRELATEDTOTHECRANIALMENINGESEpiduralspaceisapotentialspacebetweentheperiostealduraandthebonesoftheskull:siteofepiduralhematomas.Subduralspaceisthepotentialspacebetweenthemeningealduraandthearachnoidmembrane:siteofsubduralhematomas.SubarachnoidspaceliesbetweenthearachnoidandpiamatercontainingCSF:siteofsubarachnoidhemorrhage.

MENINGES

EPIDURALHEMATOMAAnepiduralhematomaresultsfromtraumatothelateralaspectoftheskullwhichlaceratesthemiddlemeningealartery.Arterialhemorrhageoccursrapidlyintheepiduralspacebetweentheperiostealduraandtheskull.

MENINGES

EXTRADURALHAEMATOMASeparationofthedurafromtheunderlyingperiosteumrequiressignificantforce,andconsequentlyoccursonlywhenhigh-pressurearterialbleedingoccursintothevirtualspace.

EPIDURALHEMATOMAEpiduralhemorrhageformsalens-shaped(biconvex)hematomaatthelateralhemisphere.Epiduralhematomaisassociatedwithamomentarylossofconsciousnessfollowedbyalucid(asymptomatic)periodofupto48hours.Patientsthendevelopsymptomsofelevatedintracranialpressuresuchasheadache,nausea,andvomiting,combinedwithneurologicalsignssuchashemiparesis.Herniationofthetemporallobe,coma,anddeathmayoccurrapidlyifthearterialbloodisnotevacuated.

MENINGES

SUBDURALHEMATOMAAsubduralhematomaresultsfromheadtraumathattearssuperficial(“bridging”)cerebralveinsatthepointwheretheyenterthesuperiorsagittalsinus.Asubduralhemorrhageoccursbetweenthemeningealduraandthearachnoid.

MENINGES

Subduralhemorrhageformsacrescent-shapedhematomaatthelateralhemisphere.Largesubduralhematomasresultinsignsofelevatedintracranialpressuresuchasheadacheandnausea.Smallorchronichematomasareoftenseeninelderlyorchronicalcoholicpatients.Overtime,herniationofthetemporallobe,coma,anddeathmayresultifthevenousbloodisnotevacuated.

SUBARACHNOIDHEMORRHAGEAsubarachnoidhemorrhageresultsfromaruptureofaberryaneurysminthecircleofWillis.ThemostcommonsiteisintheanteriorpartofthecircleofWillisatthebranchpointoftheanteriorcerebralandanteriorcommunicatingarteries.Othercommonsitesareintheproximalpartofthemiddlecerebralarteryoratthejunctionoftheinternalcarotidandposteriorcommunicatingarteries.Typicalpresentationassociatedwithasubarachnoidhemorrhageistheonsetofasevereheadache.

MENINGES

EXTRADURALHAEMATOMAThiscanresultfromdamagetoanyarterialvessel,commonlyfollowingskullfracture.

MENINGES

EXTRADURALHAEMATOMATheclassicsiteforsuchinjuryisalongthecourseofthemiddlemeningealartery,whereadirectblowcausingabonefracturecanrupturethearteryandcauserapidcollectionofanextraduralhaematoma.

EXTRADURALHAEMATOMAThehaematomaisunderconsiderablepressurebecauseofthearterialbloodpressurefeedingitandtheresistanceofferedbythestrongadhesionbetweenduraandperiosteum.

SUBDURALHAEMATOMAThecharacteristicsofasubduralhaematomadifferfromtheextraduralhaematoma.Clinicallytheaccumulationisoftenofrelativelylowpressureandseldompresentsasamedicalemergency:evensizeableaccumulationsmaybetoleratedonachronicbasiswithmildornosymptoms.

MENINGES

THEBASALGANGLIA

BASALGANGLIAThesecompactmassesofgreymatteraresituateddeepinthesubstanceofthecerebralhemisphere.Thesecompactmassesofgreymattercomprisethecorpusstriatum(composedofthecaudatenucleus,theputamenandtheglobuspallidus)andtheclaustrum.Togetherwiththecerebellum,theyareinvolvedinco-ordinationandcontrolofmovement.Thetermbasalgangliaisusedtodenoteanumberofsubcorticalnuclearmassesthatlieintheinferiorpartofthecerebralhemisphere,incloserelationwiththeinternalcapsule

BASALGANGLIA

BASALGANGLIAThetraditionaldefinitionofthebasalgangliaincludedthecorpusstriatum,claustrum,andamygdaloidcomplex.Thecorpusstriatumconsistsofthecaudatenucleus,putamenandglobuspallidusBecauseoftheircloseproximity,theputamenandglobuspalliduswereonceconsideredasthelentiform(lenticular)complexornucleus.Theputamenandcaudatenucleusshareacommonchemocytoarchitectureandconnections,andtheyarereferredtojointlyastheneostriatumorsimplythestriatum.

BASALGANGLIA

GROUPINGOFTHEBASALNUCLEI(GANGLIA)Thestriatumconsistsofthecaudatenucleusandputamen.Thelentiformnucleusconsistsoftheglobuspallidusandputamen.Thecorpusstriatumconsistsofthelentiformnucleusandcaudatenucleus.Theclaustrumliesbetweenthelentiformnucleusandtheinsularcortex.

BASALGANGLIA

Thecaudatenucleusisalargehomogeneousmassofgreymatterconsistingofahead,anteriortotheinterventricularforamenandformingthelateralwalloftheanteriorhornofthelateralventricle;abody,formingthelateralwallofthebodyoftheventricle;andanelongatedtail,whichformstheroofoftheinferior(temporal)hornoftheventricle.

BASALGANGLIA

Thecaudatenucleusislargelyseparatedfromtheputamenbytheinternalcapsule,butthetwostructuresareconnectedanteriorly.

Theputamenisaroughlyovoidmasscloselyappliedtothelateralaspectoftheglobuspallidus;together,theyarecalledthelentiformnucleus.

BASALGANGLIA

Thecorpusstriatumreceivesafferentconnectionsfromthecerebralcortexandsendsefferentstotheglobuspallidus.Fromthere,fibresprojecttothethalamusand,thence,backtothepremotorcortex.

Thebasalgangliaplayimportantmotorfunctionsinstartingandstoppingvoluntarymotorfunctionsandinhibitingunwantedmovements.

BASALGANGLIA

Thebasalgangliaconsistsof3nucleimassesdeepinthecerebrum(caudatenucleus,putamen,andglobuspallidus),onenucleusinthemidbrain(substantianigra),andthesubthalamicnucleusofthediencephalon.

Thestriatumcombinesthecaudatenucleusandtheputamenwhilethecorpusstriatumconsistsofthese2nucleiplustheglobuspallidus.

Thereare2parallelcircuits(directandindirect)throughthebasalganglia.Thesecircuitsreceiveextensiveinputfromthecerebralcortexthatprojectbacktothemotorcortexafterarelayintheventrolateral(VL)nucleusofthethalamus.Bothofthesepathwaysdemonstratedisinhibition.Thedirectpathwayincreasesthelevelofcorticalexcitationandpromotesmovement.Theindirectpathwaydecreasesthelevelofcorticalexcitationandsuppressesunwantedmovement.Allbasalgangliaconnectionsarewithipsilateralcortex.

BASALGANGLIA

THEDISORDERSOFTHEBASALGANGLIA:Disordersofthebasalgangliaareprincipallycharacterizedbyabnormalitiesofmovement,muscletoneandposture.

BASALGANGLIA

THEDISORDERSOFTHEBASALGANGLIA:-aninabilitytoinitiateandexecutewantedmovements(asinParkinson’sdisease)-aninabilitytopreventunwantedmovements(asinHuntington’sdisease).

THEDISORDERSOFTHEBASALGANGLIA:PARKINSONDISEASEClinicalManifestations:bradykinesia,cogwheelrigidity,pill-rolling(resting)tremor,shufflinggate,stoopedposture,maskedface,depression,dementia

BASALGANGLIA

THEDISORDERSOFTHEBASALGANGLIA:HUNTINGTONDISEASEClinicalManifestations:chorea(multiple,rapid,randommovements),athetosis(slow,writhingmovements),personalitychanges,dementia.Onset:20−40years.