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Download SBI4U - sheep brain dissection REVISED
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SBI4UHomeostasisUnit Name:_______________________________________ Lab–SheepBrainDissection TextbookReference:pg.427-430 Purpose: Tostudythestructureandfunctionofthemammalian(sheep)brain. Materials:safetygoggles,scalpel,probe,gloves,dissectingtray,diagrams,forceps,newspapers,textbook(s) SafetyPrecautions:1)Donotwearcontactlenseswhiledissecting,2)Takeprecautionwhenusingthescalpel, 3)Alldissectedmaterialmustbedisposedofbytheteacher. Procedure: Part1:ExternalStructure (a)Usingtheprojectedimageatthefrontoftheroom,labelthefollowingterms:anterior,posterior,dorsal, lateral,medial,ventralandmid-sagittalviewsofthebrain 1.Obtainasheepbrain,examinethedorsal,lateral,andventralviewsandidentifythethreemajor structuresthatareeasilyseen: • Thelargecerebrumiscomposedofthetwocerebralhemispheres.Theyformthelargest partofthebrainandalsomakeupthelargestpartoftheforebrain. Check: • Thecerebellumisthehighlyconvolutedstructurebehindthecerebrumandabovethebrain stem.Thecerebellumispartofthehindbrain. • Thebrainstemextendsfromthespinalcord(thecutregion)throughthebaseandpartof thecentralinteriorofthebrain. 2.Examinethecerebrumandnotetheconvolutedappearanceofitssurface.Amembranecalled themeningescoversthesurfaceofthecerebrum.Thishasbeenremovedforyou.However,note theremnantsofthemeninges. (b)Namethethreemembranesthatmakeupthemeninges. ___________________________,_____________________________and______________________________ 3.Theconvolutionsareformedbytheraisedareasorridges,calledgyri(gyrus–singular),andthedepressedareas, calledfissures.Themajorfissuresdividetheimportantlobesofthecerebrum.Themammaliancerebrumismuchmore convolutedthanthebrainsofothervertebrates,suchasbirds,reptiles,amphibians,andfish. (c)Whatisthesignificanceoftheseconvolutions? Note:thisisnotinyourtextbook. 4.Refertoadiagramofthehumanbraintohelpyoulocatethe lobesofthesheepcerebrum.Noteanydifferencesand similaritiesinthecerebrums. (d)Listthecerebrallobes. * * *notrequiredto knowthis 5.Locatethehighlyconvolutedcerebellum,whichliesposteriortothecerebralhemispheres.Comparethe cerebellumofthesheepbrainwithamodelordiagramsofthehumanbrain.Notethatthesheepbrainisnot dividedlongitudinally,asisthehumancerebellum. (e)Whatisthefunctionofthecerebellum? 6.Examinetheventralsurfaceofthesheepbrainandlocatethemedullaoblongata,whichbeginswherethe spinalcordwidens,justbelowthecerebellum.Themedullaoblongatacontainsregionswheremotornerves fromtherightsideofthecerebrumcrossovertotheleftsideofthespinalcord,andviceversa.Somesensory nervestravellingtothebrainalsocrossoverinthemedulla,andotherscrossoverwherethenerveentersthe spinalcord. (f)Whatvitalautonomicfunctionsarecontrolledbythemedullaoblongata?Describebothofthem. 7.Examinetheventralsurfaceofthebrain.Movingforwardfromthespinalcord,notethatjustinfrontofthe medullaoblongataisaroundedstructurecalledthepons. (g)Whatisthefunctionofthepons? 8.Belowthehypothalamusandinfrontofthemammillarybodyistheinfundibulum,thestalktowhichthe pituitaryglandisattached.Thepituitaryglandmaynotbepresent,asitissometimesbrokenoffduring preparationofthebrain.Thesestructureswillbediscussedingreaterdetailinthenextchapter. Locatetheinfundibulum. 9.TheopticchiasmaformsanXinfrontoftheinfundibulum. (h)Explainthesignificanceoftheopticchiasmainrelationtotherightandleftretinasandtherightandleft occipitallobes.Note:thisisnotinyourtextbook. 10.Locatetheolfactorybulbsinfrontoftheopticchiasma,atthebaseofthefrontallobesofthecerebrum. (i)Describethefunctionoftheolfactorybulbs. Part2:InternalStructure Carefullyseparatethetwohemispheresandusingascalpel,dissectthebraininthe sagittalplane. 11.Observetheinternalviewofasheepbrainthathasbeendissectedinthesagittalplaneandlocatethefollowing structures: cerebrum,corpuscallosum,hypothalamus,pituitarygland(ifpresent),cerebellum,medullaoblongata, spinalcord,pons,opticchiasma,andolfactorybulb. 12.Locatethecorpuscallosum. (j)Describethefunctionofthecorpuscallosum. Takethescalpelandcarefullycutapieceofthecerebellum(inthesagittalplane). 13.Notethedifferenceincolouroftheouterandinnerregionsofthecerebellum.Notealsohowthis colourdifferencefollowstheconvolutions.Thisisalsocharacteristicofthecerebrum. (k)Whyaresomepartsofthecerebellumandcerebrumgreyandotherswhite?Inotherwords,explain whatgreymatterandwhitematterareandhowthecolourdifferencearises. 14.Locatethefourventriclesofthebrain.Theventriclesarefilledwithcerebrospinalfluid,whichalso surroundsthebrainandthespinalcordbeneaththemeninges. (l)Whatistherole(s)ofthecerebrospinalfluid? * * * * * * * * * SheepDissectionPowerPointQuiz–Youwillbeaskedtoidentifythepartsofthebrainandstatethefunction. Refertothispackagetoassistyouinpreparingforthedissectionquiz.
