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3/17/2016

University of Guelph, Psychology: Sheep Brain Laboratory Manual©

Contents http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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Introduction...........................................................................3 TheVentralSurface................................................................4 TheMidSagittalCut...............................................................12 TheHippocampalDissection...................................................15 CoronalCuts..........................................................................23 HorizontalCuts......................................................................32 PrintThisDocument............................................................... ViewPdfVersionofthisDocument......................................... ViewPdfVersionoftheGlossary............................................

Introduction Welcometothelaboratory componentofPSYC*2410.The purposeofthislabistointroduce youtothegrossanatomyofthe brain.Sheepbrainsareusedinthis labbecausetheyareeasyto extract,reasonablyinexpensive (theyareprocuredfromthefood industry),large,andmammalian.

Beforewebeginourdissections,youshouldacquaintyourselfwiththedirectionaltermsusedin anatomy.Astructureisanteriortoanotherstructurewhenitisclosertothenoseofananimal(seethe abovediagram).Sometextsusethetermsanteriorandrostralinterchangeably,butwewillstickto http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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anterior.Astructurethatisposteriortoanotheriscloserto thebackofthehead.Anotherwordforposterioriscaudal. Downisventral.Tolookattheventralsurfaceistolookat thebottomofthebrain.Dorsalisupinthebrain(andupin thespinalcordofanimals,butnotinhumans–whyis this?).Whenastructureislateraltoanotherstructure,itis consideredtobeclosertotheoutside(seediagramtothe left).Whenastructureisclosertothemiddle(orthe midline)itisconsideredtobemedialtoanotherstructure. Youshouldmemorizetheseterms,theyareusedthroughoutthismanual.

TheVentralSurface

Webeginourexplorationofthesheepbrainwiththeventralsurface.First,wewillorientourselvesby examiningsomeofthelargerstructures.Thenwewillproceedbyrelatingthesestructurestothemajor subdivisionsofthebrain.Finally,wewillexaminethecranialnerves. Plate1:Someofthestructureswewishtostudyareobscuredbythepituitarygland(7).Plate1shows http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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theventralsurfaceofthebrainwithoutthepituitarygland.Toremovethepituitaryglandcutthroughthe trigeminalnerves(18),theabducensnerves(19)andtheinfundibulum,astalkattheanteriorendof thepituitarythatattachesittotheforebrain.

MajorStructuresoftheVentralSurface:Theanteriorventralsurfaceistakenupbytheventralportionof thefrontalcortex(1)andtheolfactorybulbs(2).Ourlaboratoryspecimensoftenonlyhaveamangled portionoftheolfactorybulbs,butwecanseethelateralolfactorytract(5)andthemedialolfactory tract(6)quitewell.Thesetractstravelfromtheolfactorybulbstotheperiamygdaloidcortex(3),and canbedistinguishedfromthesurroundingtissuebyvirtueoftheirmyelincoatedfibres.Myelination givesfibresawhitishappearance.Posteriortotheolfactorytractsyoucanseetheopticchiasm(4).Just behindtheopticchiasm,thereisalittleroundbulge,oftenwithasmallvisibleopening.Thisiswherethe pituitarygland(7)wasattachedtothebrain.Posteriortothisyouwillalsoseearoundprotuberance, themammillarybodies(8).Theterm"bodies"isusedbecauseinsomeanimalsonecandistinguishboth aleftandarightportion.Inthesheep,asyoucansee,thetwoarefusedintooneroundmidlinestructure. Posteriorandlateraltothemammillarybodiesarethecerebralpeduncles(9).Thesetwomassiveridges routemuchoftheinformationthattravelstoandfromthebrain.Thepons(10),aprominentbulge(What doesponsmean?Hint:it’sLatin),delineatesthepointwherethecerebralpedunclesdisappearfromview. Theponsislargelymadeupoffibresthattravelfromtheforebraintothecerebellum.Eventually,these fibresascendasmossyfibresintothecerebellarcortex.Fromthesheersizeofthepons,youcanimagine thatitisanimportantfibreconnection.Behindtheponsisasmalltransverse(bythiswemeanthatit runsfromlefttoright,ratherthanfromfronttoback)ridgethatisknownasthetrapezoidbody(11) (notethattheVIthnerveemergesfromhere).Behindthetrapezoidbodyyouwillfindtwomassivefibre bundlesthatrunjustdownthemidlineoneitherside.Theseareformedbythefibresofthepyramidal tract(12).Whenthefibrescrossoverabulgeinthetractiscreated(isthisadecussationora commissure?).NotethattheedgeofthebulgeiswherenerveXIIemerges.Behindthis,thespinalcord begins.Theolive(13)islocatedlateraltothepyramidaltract.Now,letusrelatethesesubstructuresto themajordivisionsofthebrain. (Fineprint:Acommissureisformedwhenfibresextendfromastructureononehalfofthebraintoatwinstructureonthe otherhalfofthebrain,formingabridgebetweenthehemispheres.Adecussation,ontheotherhand,isformedwhenfibresgo fromonestructuretoanothercompletelydifferentstructureontheotherhalfofthebrain).

http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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TheMajorSubdivisionsoftheBrain:TheTELENCEPHALON,ortheforebrain,extendsfromthefront ofthebraintotheposteriormarginoftheopticchiasm.Allofthecortex,oneithersideofthebrainstem, isalsoconsideredpartofthetelencephalon.TheDIENCEPHALONextendsfromtheposteriormargin oftheopticchiasmtojustbehindthemammillarybodies.Theventralregionofthediencephalonwhich iswhatyouarelookingat,containsthehypothalamus(thisisrightaboveandaroundthepointwherethe pituitaryglandwasattachedtothebrain).TheMESENCEPHALONextendsfromjustbehindthe mammillarybodiestotheanteriormarginofthepons.Thisstructurecontainsthesuperiorcolliculiwhich wewillencounterwhenwelookatthedorsalsurfaceofthebrainsteminthehippocampaldissection. TheMETENCEPHALONisdelineatedmoreorlessbytheponsontheventralsurfaceofthebrainand onthedorsalsurface,itextendsfromjustbehindtheinferiorcolliculusto,roughly,theposteriorpartof thefourthventricle.TheMYELENCEPHALONextendsfromjustbehindtheponstothebeginningof thespinalcord,roughlywherethepyramidaltractfibresbegintocross. TheCranialNerves:Thecranialnervesprovidesensoryinputtothebrainfromthevisual,acoustic, gustatoryandolfactorysensoryorgans.Theyalsotransmitsensoryinformationfromskinandmuscles. Onedistinguishesbetweengeneralsensoryinput(example;touchandpain),visceralsensoryinput (example:informationthatleadstonausea),andspecialsensoryinput(example:hearing,taste,vision, balance,smell). Outputisdirectedatvariousmuscles(suchasthemusclesthatmovetheeyesandthemusclesusedin chewingandspeaking),andtotheglandsoftheheadregion.Anatomistsdistinguishbetweensomatic motor(example:outputtomusclesthatmovetheeyes)branchialmotor(example:outputtomuscles http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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usedinfacialexpressionandchewing)andvisceralmotor(example:outputtomusclesthatconstrictthe pupilsoftheeye,outputtoglandsandoutputtovisceralorgans). Agivencranialnervemaybeinvolvedwithawholecollectionofthesesystems.Asanexample,the glossopharyngealnerve(IX)providesbranchialmotoroutputtothepharynxandlarynx,visceral motoroutputtotheparotidgland,carriesvisceralafferentinformationfromthecarotidsinus,general sensoryinformationfromtheposteriorthirdofthetongue(touchandpain)andspecialsensory information,alsofromtheposteriorthirdofthetongue(taste).Youcanimaginethatthepointsoforigins ofthefibresthattravelsonicelyinthisnerveareananatomicalnightmare.Youdon'thavetomemorize anyofthisbutforthosewhoareinterested,anygoodtextinhumanneuroanatomywillbringfurther clarification.Wearemostlyconcernedwiththelocationandgeneralfunctionsofthecranialnervesaswe canseethem,withoutpayinganyfurtherheedtothespecifics.Thenervesarenumbered,for convenience,fromItoXII.Thenumberinggoesfromanteriortoposterior.Thus,thefirstnerve encounteredisIandthelastisXII.YoucanseethepointofemergenceofmostofthenervesinPlateI above.Below,thenamesandplacesofemergencearegiven. I.Theolfactorynerve(14).Theolfactorynervescomefromtheolfactoryreceptorsandtravelinsmall bundlesthroughthesocalledcribiformplate(averythinboneatthebaseofthefrontallobes)toenter theolfactorybulbs(2).Whenourspecimenswereremovedfromtheskullsthathousedthem,the cribiformplateshearedtheolfactorynerves.Consequently,youwon’tbeabletoseeNerveI.Thebulbs, however,shouldbediscernable. II.Thisistheopticnerve(15)notreallyanerveintheconventionalsense,butpartofthebrain.As youcansee,theopticnerveisquitelarge.Itcomesfromtheeyeandreachestheopticchiasm(Greek: denotesacrossing),wheresomeofthefibrescrossovertothecontralateral(opposite)side,whilesome stayontheipsilateral(same)side.Pleasenotethatfibresfromtheeyearecalledopticnerve(15)fibres beforetheyreachtheopticchiasm(4)andarecalledoptictract(26)fibresafterthechiasm.Wewill laterseehowmostoftheoptictractfibresendinastructureknownasthethalamus. III.Thefirstofthenervesthatareinvolvedinthemovementsoftheeye,andthelargestoneofthese,the occulomotornerve(16).Thisnervesuppliesthemajorityofextraocular(whatdoesthatmean?) muscles:theinferioroblique,theinferior,medialandsuperiorrectus.Youwillseethisnerveemerging roughlyhalfwaybetweentheponsandtheopticchiasm.Comparethesizeofthisnervetotheothertwo nervesthatrunexternaleyemuscles!(IV&VI). IV.Thetrochlearnerve(17).Thisistheonlycranialnervethatdoesnotactualemergefromtheventral http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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surfaceofthebrainitemergesfromthedorsalsurfaceandcomescurvingdowninfrontofthepons (yes,whatisthepons?).Youmayhavetoprobedownbetweenthemembranesabitthenerveisvery slender.Thefactthatitemergesfromthedorsalbrainstemmeansthatyouwon'tusuallyseeitemerging fromthebrainwhenyouviewthebrainventrally(althoughyoucanseeitinPlate1).Thisnervesupplies thesuperiorobliquemuscleoftheeyehelpsyourrollyoureyes.Thename“trochlear”means"pulley" (referringtoaropepassingoverawheel). V.Thetrigeminalnerve(18).Thisisanabsolutelymassivenervethatcarriessensoryinformationfrom aregionofthefacethatcanbestbeoutlinedbyimaginingsomebodywearingafullfacemask.Italso bringsinsensoryinformationfromthemeninges(thecoveringsofthebrain)andisthusthenervethat bringsustoothachesandheadaches.Itisalsoinvolvedinchewingmovements(operationofthejaws). Thisnervecanbeseencomingoutfromthelateralaspectsofthepons.Youcanhardlymissitbecauseit issolarge. Dependingonthequalityofyourspecimen,youmayseeNerveVseparatingintothreemajorbranches (ophthalmic,maxillaryandmandibularbranchesWhatdothesenamesreferto?).PlateIonlyshowsa solidtrunkbutifyoupokeverygentlywithyourprobe,youwillseethatthetrunkofthenerveconsists oftwoparts,asmaller(minor)portionthatisthemotorportionandalarger(major)onethatisthe sensoryportion. VI.Theabducensnerve(19),runsthelateralrectusmuscleoftheeye.Thus,ifyoumoveyoureyesto theside,thisrequiresthefinelyintegratedactionoftwocranialnerves,theIIIrdandtheVIthnerve.This nerveemergesjustbehindtheponsfromalittleridgeknownasthetrapezoidbody.Insizeitis intermediatebetweenIIIandIV. VII.Thefacialnerve(20)innervatesmuchofthefacialmusculaturethatisusedinformingexpressions. Totheextentthatlipmovementsareusedinspeech,itisalsoinvolvedinspeech.Thisnerveisalso mixed,sinceitconveyssensoryinformationfromtheanterior2/3rdsofthetongue.Thisnervealso innervatestheglandsoftheheadwithexceptionoftheparotidglands.Youdon'tonlysmilewiththis nerve,butyoualsocrywithit!Thisnerveisfoundifyouproceedlaterallydownwardsfromthe abducens.Inmanyofourpreparations,thisnervecannotbeseenverywell. VIII.Thisnerveisoftencalledtheacousticnerve(21),butitisactuallycomposedofaportionthat bringsinformationfromtheinnerear(statoacoustic,cochlear)andaportionthatbringsinformation fromthelabyrinths(vestibular).Theformerportionisobviouslyinvolvedinhearingandthelatterwith thesenseofbalanceandrelatedfunctions.Thevestibulocochlearnerve(thetwoportionsofVIII)lies http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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justposteriortoVII,withthevestibularportionbeingmoreanteriorandthecochlearportionbeingmore posterior.Inmanyofourpreparations,thisnervecannotbeseenverywell. IX.Thisistheglossopharyngealnerve(22),itconveyssensoryinformationfromtheposterior1/3of thetongueandthepharynx.Somesayitalsohassomemotorfunctioninthepharyngealregion.Nerves IX,XandXIIemergeverycloselytogether,inamessylittlebundle.Itisunlikelythatourspecimens willallowyoutodistinguishbetweenIXandX,althoughyoumaybeabletorecognizeXI.Theyemerge inanteriortoposteriororderasnumbered.Thespinalaccessory(X)actuallycomesupalongsidethe uppermostportionofthespinalcordandrunsalonguntilitreachestheareawhereIXandXcomeout andthenitcurvesoutward,awayfromthebrainwiththem. X.Thisisthevagus(23),thatgivesyouheartpainandtummyaches.Thisnerveisthemajoroutflow fromtheparasympatheticdivisionoftheautonomicnervoussystemtotheviscera. XI.Thespinalaccessory(24)nerveinnervatesthemusclesthatyouusetobendyourheadandshrug yourshoulders:itrunsthesternocleidomastoidandtrapeziusmuscles.Bothofthesemusclesalsoreceive abitofinputfromcervicalmotornerves.Thisnervecontinuestoreceivelittlerootletsfromthe brainstemasitrunsalongandyoumaybeabletotellitfromXandXIasyoutraceitalong. XII.Thehypoglossalnerve(25).Fortonguewagging.NerveXIIisinvolvedinthecontrolof movementsofthetongueduringspeakingandeating.Thisnerveisquitemassive(thetongueisvery finelyinnervatedsinceithastobecapableofveryprecisemovement)andemergesfromtheposterior endofthemedullaasabunchoflaterallyspreadfibresbundlesthatmergeintoonesolidnervetrunkas thenervesextendsfromthebrain.Asmentionedbefore,youmaybeabletoseeafringealongthe pyramidaltractdecussation. Forthoseofyouwithaweakmemory,thereisalittlemnemonicdevicethatallowsyoutomemorizethe cranialnervesalphabetically:itgoeslikethis:OnOldOlympus'ToweringTopsAFinAndGerman VaultsAndHops.(No,itisnotbyByron).Plate1willgiveyouaroughorientationastowherethe cranialnervesarelocated.Unfortunately,mostofthesheepbrainswegetaredamagedinthelower portionofthebrainstemanditisnotoftenthatyoucanseeallofthenerves.Oftenyouwillonlybeable toseenervesIIVIIandXI.Fortherestyouwillhavetoconsultthedemonstrationbrainsandplatesthat aremadeavailable. Bytheendofthislabyoushouldbeabletoidentifythefollowingstructureswithoutdifficulty: Structures: 1frontalcortex http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

21vestibuloacousticnerve(notseeninPlate1) 8/51

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2olfactorybulbs 3periamygdaloidcortex 4opticchiasm 5lateralolfactorytract 6medialolfactorytract 7pituitarygland(notseeninPlate1) 8mammillarybodies 9cerebralpeduncles 10pons 11trapezoidbody 12pyramidaltract 13olive 14olfactorynerve(notseeninpicture) 15opticnerve 16occulomotornerve 17trochlearnerve 18trigeminalnerve 19abducensnerve 20facialnerve

22glossopharyngealnerve(notseeninPlate1) 23vagusnerve(notseeninPlate1) 24spinalaccessorynerve 25hypoglossalnerve 26optictract 

TheMidSagittalCut

Themidsagittalcutisastraightforwarddissection.Removethepituitarygland.Turnthebrainover. Alignyourknifeorrazorbyplacingitinthelongitudinalfissure(betweenthetwohemispheres).Using smoothsawingmotions,cutyourbraininhalf. Webeginourstudyofthemidsagittalcutwiththemassaintermedia(25),thepointatwhichthetwo http://portal.psy.uoguelph.ca/faculty/peters/labmanual/PrintSheepBrain.html

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halvesofthethalamusjoinacrossthemidline.Thisjoiningisnotseeninallmammals,orevenwithinall individualsofaspecies.Inhumansforinstance,onlyonethirdofthepopulationhasthisjoining.Dorsal tothemassaintermediaisthefornix(15).Abovethefornix,inourpicture,isoneofthelateral ventricles(8).Ithappenstobetheleftlateralventricle.Thereareatotaloffourventriclesinthebrain. Thefirstventricleistheleftlateralventricle.Thesecondventricleistherightlateralventricle.Thethird ventricle(9)surroundsthemassaintermedia.Thecerebralaqueduct(10)whichbeginsjustbehindthe mostventralandposteriorpartoftheanteriorcommissure(14),connectsthethirdventricleandthe fourthventricle(11).Thefourthventricleissituatedunderneaththecerebellum(1).Mercifullywe won’tbotherwithnamingallofthelobesofthecerebellum,butinalaterlabwewilldistinguish betweentheanteriorandposteriorlobe.Therefore,itisimportantforyoutonotetheprimaryfissure(2) whichdifferentiatesthesestructures.Wealsosee,belowthecerebellum,thepons(24),whichisformed bymassivefibrebundlesontheirwaytothecerebellumfromthebrain. Thenumbers(20),(21)and(22)denotethecorpuscallosum,themassivefibrebundlethatconnects uppertwohalvesofthebraininbothsheepandhumans.Theareain(21)isknownasthegenuwhilethe areadenotedbythenumber(22)isknownasthesplenium.Genurefersto“knee”andyoucanremember thatthekneepointsforwardandthegen...