02 lecture twocentral nervous systemgross organization.docx

02 lecture twocentral nervous systemgross organization.docx

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02lecturetwocentralnervoussystemgrossorganization

Lecturetwo

CentralNervousSystem—GrossOrganization

Scope:

Inthislecturewewilldiscussthegrossoroverallorganizationofthenervoussystem,anddefinesomeimportanttermsandconcepts.HerewewillbeconcernedprimarilywithareasoftheCNSthatcanbeviewedexternally;wewillbereturningtoamoredetaileddiscussionofthefunctionofsomeoftheseareasandstructuresinensuinglectures.

Outline

I.Beforewecandiscussthemodernviewofbrainasthebiologicalsubstrateofthemind,weneedtodefinesometermsthatwillbeusedthroughoutthecourse,andtounderstandsomethingaboutthegrossoroverallorganizationofthebrain.

A.ThetermCNSrefersspecificallytothebrainandspinalcord;thebrainiscontinuouswiththespinalcordthroughanopeningintheskull（foramenmagnum）.

B.Theperipheralnervoussystem（PNS）consistsofneuronsand/ornervouslocatedoutsideofthebrainandspinalcord.Anexampleisthesciaticnervethatrunsdownthebackoftheleg.

II.IfwelookedattheCNSfromtheoutside,wewouldseethefollowingparts.

A.Thespinalcord,whichisprotectedbyourbonyvertebrae.

B.Partofthebrainstem,whichisaphylogeneticallyolderareaofthebraincontinuouswiththespinalcord.

C.Thehemisphere;inhumans,muchofthebrainstemiscoveredbythetwocerebralhemispheres.

III.Thereareanumberofreferencetermsthatareusedtorefertodifferentareasofthebrainandspinalcord,andtotherelativepositionofstructure;someofthesetermsareshowninrelationtoadrawingofthebraininFigure2.1.

A.Thetermsrostral（towardsthefrontof“head”end;anterior）andcaudal（towardsthebackor“tail”end;posterior）areusedgenerallytorefertothefrontandbackofthebrain,respectively.

B.Thetermsdorsalandventralareusedtorefertothetopandbottom（orunderside）ofthebrain.

C.Thetermsmedialandlateralareusedinreferencetothebodymidlinewithmedialtowards,andlateralawayfrom,themidline.

IV.Theadultbraincanbesubdividedgrosslyalongarostral-caudaldimensionintofiveregions（Figure2.1）;howtheseregionsdevelopwillbeoneofthetopicsofafuturelecture.

A.Thetelencephalonistherostral-mostsubdivisionofthebrainconsistingofthetwocerebralhemispheres;thetelencephalonisthemostrecentlyevolvedareaofthebrainanditsfunctionwillbethefocusofmanylecturesinthiscourseexploringtherelationshipbetweenmindandbrain.Itistheoutersurfaceofthetelencephalon（cortex）,whichisbelievedtobetheseatofthemind.

B.Thediencephalonincludesthethalamus（anteroom）,animportantstructureconsistingofanumberofdistinctareas/structures,manyofwhichwillprojectto（e.g.,beconnectedto）thecerebralcortex,andhencethename“anteroom”;thehypothalamuswhichis“below”thethalamusandalsocomposedofanumberofindividualareas,isresponsibleforthecentralcontrolofhomeostasisinthebody.

C.Themesencephalonormidbrain,lyingbetweenthediencephalonandthemetencephalon;anumberofstructuresinthispartofthebrainareinvolvedinreflexes.

D.Themetencephalon（“between”brain）consistsoftwomajorstructures,thecerebellum（thelargeball-shapedstructureonthebaseofthebrain）,andthepons（bridge）whichconnectsthecerebellumtotherestofthebrain.

E.Themyelencephalon（longwhitemarrowstructure）isalsoreferredtoasthemedullaormedullaoblongata,andisso-namedbecauseitcontainsmanyofthelongpathwaysortracts（axonsorprocessesofneuronstravelingtogetherinabundle）inthebrain,forexample,axonsprojectingtothespinalcord;itisthemedullawhichiscontinuouswiththespinalcordattheforamenmagnum.

V.Othergeneraltermsarealsocommonlyusedtorefertodifferentbrainsubdivisions.

A.Theforebrainreferstotherostra-mostsubdivisionsofthebrain,andincludesthetelencephalonandthediencephalon;theforebrainisthemostrecentlyevolvedareaofthebrainphylogenetically.

B.Thehindbrainconsistsofthecaudalbrainsubdivisionsandincludesthemetencephalonandthemyelencephalon.Forexample,themedullawouldbeconsideredastructureofthehindbrain;thehindbrainisconsideredaphylogeneticallyolderormoreprimitivepartofthebrain,controllingvital,butlargelyunconsciousorsubconscious,functionssuchasbreathingandheartrate.

C.Thebrainstemisacollectivetermusedtorefertothemesencephalon,metencephalon,andmyelencephalon;likethehindbrain,thebrainstemisconsideredanolderareaphylogenetically.

VI.Inthenextlecture,wewillseethatinternally,thebrainisalsoorganizedintodifferentareas.

FutureReading:

Anyrecentneurosciencetextwillcovermostofthebasicinformationcoveredinthislecture,althoughinmuchgreaterdetail.TheauthoritativebookinneuroscienceisPrinciplesofNeuralscience,editedbyE.R.Kandel,J.H.Schwartz,andT.M.Jessell.

QuestionstoConsider:

1.Whatarethefivesubdivisionsoftheadulthumanbrainfromrostraltocaudal?

Whydoyouthinkthetelencephalonissolargeinhumans?

2.Sometimesthemeaningofanamegivesacluetoitsfunction.Whyisthethalamustheanteroom?

LectureTwo—Transcript

CentralNervousSystem—GrossOrganization

Welcomeback.Inourintroductorylecture,itwasstatedthatthemodernviewisthatcognitionandperceptionaretheresultofthebrainprocesses.Thetruthisthateverysinglethingyoucanhear,feel,see,everythoughtyouthink,istheresultofthebrainprocesses.Butbeforewecangetintotalkingaboutsomeofthesetopics,weneedtodefinesomeimportanttermssoweareallonthesamepageabouthowweuselanguage.Andweneedtounderstandsomeverybasicprinciplesabouthowthebrainisorganized.Sothenextfewlecturesaregoingtoprovidethatfoundationmaterialonwhichtherestofthecourseisgoingtobebased.Theterms,definitions,andotherthingswewilltalkaboutandlearninthefirstpartofthecoursearegoingtobeimportantforunderstandalloftheotherlectures.

Inthisspecificlecturewhatwewanttodoistalkaboutthe“grossorganizationofthebrain,”andtheterminneuroscienceisusedtomeantheexternalfeaturesofthebrain,whatcanbeseenwithouttheaidofamicroscope.Sowhenwetalkaboutthegrossorganization,it’stheoverallbig,largeorganizationofthebrain.

Wearegoingtoreturntoadiscussionoffunctionofindividualareasatalatertime,butherewearegoingtolearnsomedefinitionsandtermssothatweallknowwherewearewhenwetalkaboutthebrain.

So,let’sstartwithsomeofthosebasicdefinitions.Theterm“centralnervoussystem”referstothebrainandthespinalcord.Thebrainiscontinuouswiththespinalcordthroughaholeintheskull,whichiscalledtheforamenmagnum.Youallknowthatyourspinalcordisinfactprotectedbybonyvertebraandthatyourbrainisinthiscompartmenthere.Andthebrainandspinalcordhavetobecontinuous,sothereisaholeinthebottomoftheskull.Andthisiswherethebrainandthespinalcordarecontinuous.

Thiscourseisgoingtofocusprimarilyonthebrain,soonthatpartofthecentralnervoussystem.Butthereisanotherpartofthenervoussystemthatwearen’tgoingtocoverinthiscourse,andthat’scalledtheperipheralnervoussystem.

Theperipheralnervoussystemisactuallyanante-neuralelementthatliesoutsideofthebrainandspinalcord.Sotheperipheralnervoussystemwouldbe,forexample,youhavealongnervecalledthe“sciaticnerve”thatrunsdownthebackoftheleg—thisispartoftheperipheralnervoussystem.Anypartofanervousstructure,whetherit’sanervecelloraprocessofanervecell,whichliesoutsideofthebrainandspinalcord,wouldbepartoftheperipheralnervoussystem.

Now,throughoutthiscoursewearegoingtobeusingwhatIcallthehandydandybrainmodel.Thisbeautifulmodelwithallofthesedifferentcolors—youturnitlikethis,youcanseeitfromdifferentsides—theoneinyourheadisactuallymuchmorebeautifulthanthat,butthisistheonlymodelthatIhad.Wearegoingtobeusingthiswhenwepointoutdifferentareasofthebrain,soit’simportantthatyoubeabletoimmediatelyorienttothismodel.

Now,justlikewehavetwosidestothebody,wehavearightandleftsidetoourbody,wehavetwohemispheresinourbrain.Thismodelisonlyonehemispheresoit’susedforteachingpurposes.Theotherhemisphere,whichwouldbelocatedhere,isnotshown.Whatwewanttoknowiswherethefrontandthebackofthebrainare,sowheneverItalkaboutsomethingandrefertothismodelthenyoucanlookatitandyou’llknowwhereweare.

Thisisthefrontofthebrainandthisisbackofthebrain.Andoneofthewaysyoucanalwaysknowthatthisisthebackofthebrainistoorienttothislittlestructurerighthere.Thislittlefist-shapedstructureiscalledthecerebellumandit’sgoingtobeatopicofoneofthelectureslateron.Butthecerebellumishereatthebaseoftheskullandsoyoucanalwaystellwherethebackofthebrainis.

TheotherthingIwantyoutonoticewiththismodelisthatthisisarighthemisphere.Sothisisthefront,thisistheback.Andthatwouldmakethisarighthemisphereofthebrain.SowhenwetalkaboutthesedifferentstructuresandIpointthingsoutonthismodel,thenyou’llknowbasicallywhereyouareat.

Nowwehavelookedatthecentralnervoussystemfromtheoutside;soweimaginethatthiswasourbrainandwearegoingtolookatitfromtheoutside.Ifwelookdownhere,wewouldseethespinalcord.Soagain,thespinalcordispartofthecentralnervoussystem,anditisp