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ORBITS THEWALLSOFTHEORBIT protectandcontain • theeyeballs • andaccessoryvisualstructures,whichincludethe: • eyelids,whichboundtheorbitsanteriorly,controllingexposureof theanterioreyeball, • extraocularmuscles,whichposi:ontheeyeballsandraisethe superioreyelids, • nervesandvesselsintransittotheeyeballsandmuscles, • orbitalfasciasurroundingtheeyeballsandmuscles, • mucousmembrane(conjunc:va)liningtheeyelidsand • anterioraspectoftheeyeballsandmostofthelacrimalapparatus, • andorbitalfat. THEWALLSOFTHEORBIT Thebonyelementsoftheorbitalwallsarethe: ROOF orbitalplateofthefrontalboneandlesserwingofthesphenoid FLOOR orbitalsurfaceofthemaxillaandcontribu:onsfromthezygoma?c andpala?nebones LATERALWALL frontalprocessofthezygoma:cboneandgreaterwingofthe sphenoid MEDIALWALL orbitalplateoftheethmoid,thelacrimalbone,thefrontalprocessof themaxilla,andthebodyofthesphenoid. THEWALLSOFTHEORBIT Eachorbitalwallhasseveralimportantadjacentrela:onships: ROOF anteriorcranialfossa,frontalsinus,andfrontallobesofthebrain FLOOR maxillarysinusandinfra-orbitalnervesandmuscles MEDIALWALL ethmoidalcells,sphenoidalsinuses,andnasalcavity LATERALWALL temporalfossa APEX middlecranialfossa,temporallobesofthebrain,infratemporalfossa,and pterygopala:nefossa. THE EYELIDS AND LACRIMAL APPARATUS Thelayersoftheeyelids,fromanteriortoposterior,consistof: • skin • subcutaneous:ssue • voluntarymuscle • orbitalseptum • tarsus • palpebralconjunc:va THE EYELIDS AND LACRIMAL APPARATUS THELACRIMALAPPARATUSconsistsofthe: • Lacrimalgland • Excretoryductsoflacrimalgland • Lacrimalcanaliculi • Nasolacrimalduct THE EYELIDS AND LACRIMAL APPARATUS THELACRIMALAPPARATUSconsistsofthe: Lacrimalgland:secreteslacrimalfluidawateryphysiological salinecontainingthebacteriocidalenzymelysozyme.Thefluidmoistensand lubricatesthesurfacesoftheconjunc:vaandcorneaandprovidessome nutrientsanddissolvedoxygentothecornea;whenproducedinexcess,it cons:tutestears. Excretoryductsoflacrimalgland:conveylacrimalfluidfromthelacrimal glandstotheconjunc:valsac. Lacrimalcanaliculi:commenceatalacrimalpunctum(opening)onthe lacrimalpapillanearthemedialangleoftheeyeanddrainlacrimalfluidfrom thelacrimallake(atriangularspaceatthemedialangleoftheeyewherethe tearscollect)tothelacrimalsac(thedilatedsuperiorpartofthenasolacrimal duct). Nasolacrimalduct:conveysthelacrimalfluidtotheinferiornasalmeatus (partofthenasalcavityinferiortotheinferiornasalconcha). THE EYELIDS AND LACRIMAL APPARATUS Thelacrimalglandsreceivesecretomotorparasympathe?cfibersfrom thefacialnerve(CNVII)thatoriginateinthesuperiorsalivatory nucleus.Thesepreganglionicparasympathe:cfiberstravelinthe greaterpetrosalnerveandthenbythenerveofthepterygoidcanal tothepterygopala?neganglion,wheretheysynapsewiththecell bodyofthepostsynap:cfiber.Postganglionicparasympathe:cfibers travelthroughthemaxillarynerve(V2)-zygoma?cnerve,and lacrimalnerve(V1)tothelacrimalgland. Thezygoma?cnerve(fromthemaxillarynerveCNV2)bringsboth typesoffiberstothelacrimalbranchoftheophthalmicnerve,by whichtheyenterthegland. THE EYELIDS AND LACRIMAL APPARATUS Postganglionicsympathe?cnervesfromthesuperiorcervicalganglion jumpfromtheinternalcaro:dplexusintheformofthedeeppetrosal nerve,jointhegreaterpetrosalnerve,andformthenerveofthe pterygoidcanal.Thesepostganglionicsympathe:cfibersthenfollow thesamecourseuptothelacrimalglands. Thesensoryinnerva?onofthelacrimalglandisthroughthe ophthalmicdivisionCNV1ofthetrigeminalnerve,viathelacrimal branch. THE EYELIDS AND LACRIMAL APPARATUS LACRIMATIONREFLEX Thelacrima:onreflexiss:mulatedbyirrita:onoftheconjunc:vaand cornea. Theafferentlimbofthereflexinvolvesbranchesoftheophthalmicnerve withanaddi:onalcontribu:onfromtheinfraorbitalnerveiftheconjunc:va ofthelowereyelidisinvolved. Impulsesenterthebrainandspreadbyinterneuronestoac:vate parasympathe:cneuronesinthesuperiorsalivatorynucleusand sympathe:cneuronesintheupperthoracicspinalcord. Theefferentpathwaytothelacrimalglandinvolvesthegreaterpetrosal nerve,whichcarriespreganglionicparasympathe:csecretomotorfibres,and thedeeppetrosalnerve,whichconveyspostganglionicsympathe:cfibres; theparasympathe:cfibresrelayinthepterygopala:neganglion,andthe sympathe:cfibrespassthroughtheganglionwithoutsynapsing. THEEYEBALL Thethreelayersoftheeyeballarethe: 1.Fibrouslayer(outercoat)consistsofthescleraposteriorlyandthe corneaanteriorly. 2.Vascularlayer(middlecoat)consistsofthechoroidposteriorlyand iscon:nuouswiththeciliarybodyandirisanteriorly 3.Innerlayer(innercoat)consistsoftheop:cpartofthere?na posteriorlyandthenonvisualre:nathatcoverstheinternalsurface oftheciliarybodyandirisanteriorly. FIBROUSLAYER Thescleraisthetoughopaquepartofthefibrouslayer(coat)ofthe eyeball,coveringtheposterior5/6oftheeyeball. Thescleraisprovidinga[achmentforthemusclesoftheeye Thecorneaisthetransparentpartofthefibrouslayercovering theanterior1/6oftheeyeball THECORNEADOESNOTCONTAINANYVESSELS Thecorneaisinnervatedbynumerousbranchesoftheophthalmic nerve,whicheitherformananularplexusaroundtheperipheryof thecornea Thescleraisrela:velyavascular,thecorneaiscompletelyavascular. Lacrimalfluidalsoprovidesoxygenabsorbedfromtheair. Dryingofthecornealsurfacemaycauseulcera?on. 2.Vascularlayer(middlecoat)consistsofthechoroidposteriorlyand iscon:nuouswiththeciliarybodyandirisanteriorly Thechoroid,adarkreddishbrownlayerbetweenthescleraandthe re:na,formsthelargestpartofthevascularlayeroftheeyeballand linesmostofthesclera. Thevasculartunicoftheeyeconsistsof: • thechoroid, • ciliarybody, • iris, whichcollec:velyformacon:nuous structure: THEUVEA Thechoroidcoverstheinternalscleralsurfaceandiscon:nuous anteriorlywiththeciliarybody. Theciliarybody, isaring-likethickeningof thelayerposteriortothe corneoscleraljunc:on, whichismuscularaswellas vascular Theciliarybodyconnectsthe choroidwith thecircumferenceoftheiris. Theciliarybodyprovidesa[achmentforthelens.Thesmoothmuscle oftheciliarybodycontrolsthethickness,andthereforethefocus,of thelens. Theelas:ccapsuleofthelensisanchoredbyzonularfiberstothe ciliaryprocesses. Thesmoothmuscleoftheciliarybodycontrolsthethickness,and thereforethefocus,ofthelens. Theciliaryprocesses secrete aqueoushumor. Aqueoushumorfillstheanteriorsegment(chamber)oftheeyeball, anteriortothelens,suspensoryligament,andciliarybody. Theiris,whichliterallyliesontheanteriorsurfaceofthe lens,isathincontrac:lediaphragmwithacentralaperture, thepupil,fortransmi]nglight Twoinvoluntarymusclescontrolthesizeofthepupil: • theparasympathe:callys:mulated,circularlyarrangedsphincter pupillaedecreasesitsdiameter(constrictorcontractsthepupil), and • thesympathe:callys:mulated,radiallyarrangeddilatorpupillae increasesitsdiameter(dilatesthepupil) Thesympathe:cresponsesusuallyoccurimmediately,yetitmaytake upto20minforthepupiltodilateinresponsetolowligh:ng Thepupillaryreflexpathwaybeginswiththephotosensi:vere:na ganglioncells,whichconveyinforma:onviatheop:cnerveCNII. Themajorityoftractfibresendinthelateralgeniculatenucleusofthe thalamus.Thesmallnumberleavetheop:ctractbeforeitreachesthe thalamusandsynapseintheolivarypretectalnucleus. Theinforma:onisrelayedfromthepretectalnucleusbyshort neuronesthatsynapsebilaterallyonpreganglionicparasympathe:c neuronesintheEdinger–Westphalnucleus. Efferentimpulsespassalongparasympathe:cfibrescarriedbythe oculomotornervetotheorbit,wheretheysynapseintheciliary ganglion.Postganglionicfibrestravelintheshortciliarynervestothe sphincterpupillae,whichreducesthesizeofthepupilwhenitcontracts. Sympathe?cpreganglionicfibresarisefromneuronesinthelateral columnofthefirst(T1)andsecond(T2)thoracicsegments,andpass viathesympathe:ctrunktothesuperiorcervicalganglion. Postganglionicneuronestravelupthenecknexttotheinternal caro:darteryasthecaro:dplexus,aroundthecaro:dartery. Someoftheaxonsfromtheplexusformthesympathe:crootofthe ciliaryganglion,passingthroughtheciliaryganglionwithout synapsing;mostlytravellingintheshortciliarynerves,theyinnervate thedilator. Abnormalsustainedpupillarydila:on(mydriasis)mayoccurin certaindiseasesorasaresultoftraumaortheuseofcertaindrugs. 3.Innerlayer(innercoat)consistsoftheop:cpartofthere?na posteriorlyandthenonvisualre:nathatcoverstheinternalsurface oftheciliarybodyandirisanteriorly. Theinnerlayeroftheeyeballisthere?na. There:naconsistsof:neurallayer(lightrecep:ve)andpigmented layer(thelight-absorbing). There:naconsistsoftwofunc:onalpartswithdis:nctloca:ons: • theop?cpartofthere?na:issensi:vetovisuallightraysandhas twolayers:aneurallayerandpigmentedlayer. • thenon-visualre?na:isananteriorcon:nua:onofthepigmented layerandalayerofsuppor:ngcells. Theneurallayerislightrecep:ve. Thepigmentedlayerconsistsofasinglelayerofcellsthatreinforces thelight-absorbingpropertyofthechoroidinreducingthesca[ering oflightintheeyeball. THENON-VISUALPARTOFTHERETINAextendsovertheciliarybody (ciliarypartofthere:na)andtheposteriorsurfaceoftheiris(iridial partofthere:na),tothepupillarymargin. Theinternalaspectoftheposteriorpartoftheeyeball,wherelightentering theeyeballisfocused,isreferredtoasthefundusoftheeyeball. There:naofthefundusincludesadis:nc:vecircularareacalledthe op?cdisc(op:cpapilla),wherethesensoryfibersandvessels conveyedbytheop:cnerve(CNII)entertheeyeball Theop:cdisccontainsnophotoreceptors,theop:cdiscisinsensi:ve tolight.Thispartofthere:naiscommonlycalledtheblindspot. Justlateraltotheop:cdiscisthemaculaofthere?naormacula lutea. Theyellowcolorofthemaculaisapparentonlywhenthere:nais examinedwithred-freelight. Themaculaluteaisasmallovalareaofthere:nawithspecial photoreceptorconesthatisspecializedforacuityofvision. Atthecenterofthemaculaluteaisadepression,thefoveacentralis (centralpit),theareaofmostacutevision. Thefoveaisapproximately1.5mmindiameter. Itscenter,thefoveola,doesnothavethecapillarynetwork. Theop:cpartofthere:naterminatesanteriorlyalongtheoraserrata, theirregularposteriorborderoftheciliarybody. There:naissuppliedby thecentralarteryofthere:na, abranchoftheophthalmicartery. COMPARTMENTSOFTHEEYEBALL Theanteriorchamberoftheeyeisthespacebetween: • thecorneaanteriorlyand • theiris/pupilposteriorly. Theposteriorchamberoftheeyeisbetween: • theiris/pupilanteriorlyand • thelensandciliarybodyposteriorly. Aqueoushumorisproducedintheposterior chamberbytheciliaryprocessesoftheciliary body(vascularlayeroftheeyeball). Theanteriorandposteriorchambers oftheeyecontainaqueoushumor COMPARTMENTSOFTHEEYEBALL Aberpassingthroughthepupilintotheanteriorchamber,the aqueoushumordrainsthroughatrabecularmeshworkatthe iridocornealangleintothescleralvenoussinus TheanteriorandposteriorchamberoftheeyeareconnectedbyPUPIL Thehumorisremovedbythelimbalplexus Thehumorisremovedbythelimbalplexus. Thelimbusmarksthetransi:onalzonebetweenthecorneaandsclera. COMPARTMENTSOFTHEEYEBALL Thelens • isposteriortotheirisand • anteriortothevitreoushumorofthevitreousbody Thehighlyelas:ccapsule ofthelensisanchoredbyzonularfibers totheencirclingciliaryprocesses. Theciliarymuscleoftheciliarybodychanges theshapeofthelens. COMPARTMENTSOFTHEEYEBALL THEEYEBALL Aqueoushumorisproducedintheposteriorchamberbytheciliary processesoftheciliarybody(vascularlayeroftheeyeball). Theanteriorandposteriorchambersoftheeyecontain aqueoushumor Aberpassingthroughthepupilintotheanteriorchamber,the aqueoushumordrainsthroughatrabecularmeshworkatthe iridocornealangleintothescleralvenoussinus Thevitreoushumorisawateryfluidenclosedinthemeshesofthevitreous body,atransparentjelly-likesubstanceintheposteriorfourfibhsofthe eyeballposteriortothelens COMPARTMENTSOFTHEEYEBALL DISTANCEVIEW cillarymuscleisrelaxed zonularfibresundertension lensisthin NEARVISION cillarymusclecontracts zonularfibresrelax lensisthicker THEEYEBALL THEEXTRAOCULARMUSCLESOFTHEORBIT MOVEMENTSOFTHEEYEBALL movingthepupil: • medially-towardthemidline,adduc?onor • laterally-awayfromthemidline,abduc?on MOVEMENTSOFTHEEYEBALL movingthepupil: • superiorly-eleva:on)or • inferiorly-depression THEEXTRAOCULARMUSCLESOFTHEORBIT THERECTIMUSCLES arisingfromafibrouscuff,thecommontendinousring, thatsurroundstheop:ccanalandpartofthesuperiororbitalfissure attheapexoftheorbit SUPERIORRECTUS(SR)-OculomotornerveCNIII Elevates,adducts,androtateseyeballmedially INFERIORRECTUS(IR)-OculomotornerveCNIII Depresses,adducts,androtateseyeballlaterally THEEXTRAOCULARMUSCLESOFTHEORBIT THERECTIMUSCLES SUPERIORRECTUS(SR)CNIII Elevates,adducts,androtateseyeballmedially INFERIORRECTUS(IR)CNIII Depresses,adducts,androtateseyeballlaterally MEDIALRECTUS(MR)CNIII Adductseyeball LATERALRECTUS(LR)CNVI Abductseyeball THEEXTRAOCULARMUSCLESOFTHEORBIT THEOBLIQUESMUSCLES SUPERIOROBLIQUE(SO)-TROCHLEARNERVE(CNIV) Abducts,depresses,andmediallyrotateseyeball INFERIOROBLIQUE(IO)-OCULOMOTORNERVE(CNIII) Abducts,elevates,andlaterallyrotateseyeball THEEXTRAOCULARMUSCLESOFTHEORBIT SUPERIORRECTUS(SR)CNIII Elevates,adducts,androtateseyeballmedially INFERIORRECTUS(IR)CNIII Depresses,adducts,androtateseyeballlaterally MEDIALRECTUS(MR)CNIII Adductseyeball LATERALRECTUS(LR)CNVI Abductseyeball SUPERIOROBLIQUE(SO)-TROCHLEARNERVE(CNIV) Abducts,depresses,andmediallyrotateseyeball INFERIOROBLIQUE(IO)-OCULOMOTORNERVE(CNIII) Abducts,elevates,andlaterallyrotateseyeball LEVATORPALPEBRAESUPERIORIS-OCULOMOTORNERVE(CNIII) Theskeletalmusclethatraisestheuppereyelid. THEEXTRAOCULARMUSCLESOFTHEORBIT TROCHLEARNERVE(CNIV)innervates: • SUPERIOROBLIQUE(SO) ABDUCENTNERVE(CNVI)innervates: • LATERALRECTUS(LR)CNVI OCULOMOTORNERVE(CNIII)innervates: • SUPERIORRECTUS(SR) • INFERIORRECTUS(IR) • MEDIALRECTUS(MR) • INFERIOROBLIQUE(IO) • LEVATORPALPEBRAESUPERIORIS THEEXTRAOCULARMUSCLESOFTHEORBIT THEOBLIQUESMUSCLES Duringaphysicalexamina:on, thephysiciandirectsthepa:enttofollowhisorherfingerlaterally (tes:ngtheLRandabducentnerve[CNVI]), thensuperiorlyandinferiorlytoisolateandtestthefunc:onoftheSR andIRandtheintegrityoftheoculomotornerve(CNIII),which suppliesboth. THELEVATORPALPEBRAESUPERIORIS Elevatessuperioreyelid INNERVATION:OCULOMOTORNERVECNIII THEARTERIESOFTHEORBIT Thebloodsupplyoftheorbitismainlyfromtheophthalmicartery, abranchoftheinternalcaro:dartery Theinfra-orbitalartery,fromtheexternalcaro:dartery,also contributesbloodtostructuresoftheorbit. Theterminalpartofthefacialarteryiscalled theangularartery, itanastomoseswiththeophthalmicartery. Thecentralarteryofthere:na,abranchof theophthalmicarteryarisinginferiortotheop:cnerve. Thecentralarteryofthere:napiercesthesheathoftheop:cnerve andrunswithinthenervetotheeyeball,emergingattheop:cdisc. THEARTERIESOFTHEORBIT Theterminalbranchesareendarteries(arterioles),whichprovide theonlybloodsupplytotheinternalaspectofthere:na. Theexternalaspectofthe re:naisalsosuppliedbythe capillarylaminaofthechoroid Sixshortposteriorciliaryarteriesdirectlysupplythechoroid Twolongposteriorciliaryarteries,oneoneachside oftheeyeball,passbetweenthescleraandthe choroidtoanastomosewiththeanteriorciliary arteriestosupplytheciliaryplexus. THEVEINSOFTHEORBIT Venousdrainageoftheorbitisthroughthesuperiorandinferior ophthalmicveins,whichpassthroughthesuperiororbitalfissure andenterthecavernoussinus Atthemedialangleoftheeye,thefacialveincommunicateswith thesuperiorophthalmicvein,whichdrainsintothecavernoussinus. Theophthalmicveinsdrainblooddirectlyintothecavernoussinus. Thecentralveinofthere:nausuallyentersthecavernoussinusdirectly Thescleralvenoussinusisavascularstructureencirclingtheanterior chamberoftheeyeballthroughwhichtheaqueoushumorisreturned tothebloodcircula:on. THELYMPHATICSOFTHEORBIT Lympha:cdrainageoftheorbitistotheparo?dnodes Lensisnotsuppliedby anylymphvessels ThetrigeminalnerveCNV Thetrigeminalnerveisdividedasfollows: • ophthalmicV1division:exitstheskullviathesuperiororbitalfissure • maxillaryV2division:exitstheskullviatheforamenrotundum • mandibularV3division:exitstheskullviatheforamenovale Thetrigeminalnerveisdividedasfollows: • ophthalmicV1division:exitstheskullviathesuperiororbitalfissure Thesoma:c(general)sensoryfibersofCNV1aredistributedtoskinand mucousmembranesandconjunc:vaofthefrontoftheheadandnose ThebranchesoftheophthalmicnerveV1thatinnervatethefaceinclude: • thesupra-orbitalandsupratrochlearnerves,whichleavetheorbit superiorlyandinnervatetheuppereyelid,forehead,andscalp; • theinfratrochlearnerve,whichexitstheorbitinthemedialangleto innervatethemedialhalfoftheuppereyelid,theskinintheareaofthe medialangle,andthesideofthenose; ThetrigeminalnerveCNV ThebranchesoftheophthalmicnerveV1thatinnervatetheface include: • thesupra-orbitalandsupratrochlearnerves,whichleavetheorbit superiorlyandinnervatetheuppereyelid,forehead,andscalp; • theinfratrochlearnerve,whichexitstheorbitinthemedialangle toinnervatethemedialhalfoftheuppereyelid,theskininthe areaofthemedialangle,andthesideofthenose; • thelacrimalnerve,whichexitstheorbitinthelateralangleto innervatethelateralhalfoftheuppereyelidandtheskininthe areaofthelateralangle;and • theexternalnasalnerve,whichsuppliestheanteriorpartofthe nose. THENERVESOFTHEORBIT THEOPTICNERVECNII Theop:cnerves(CNII)havesensoryfibersconcernedwiththe specialsenseofvision. Theop:cnervefibersarisefromganglioncellsinthere:na. Thenervefibersexittheorbitviatheop:ccanals;fibersfromthe nasalhalfofthere:nacrosstothecontralateralsideattheop:c chiasm. Thenervefibersthenpassviatheop:ctractstothegeniculate bodiesofthethalamus,wheretheysynapseonneuronswhose processesformtheop:cradia:onstotheprimaryvisualcortexof theoccipitallobe. THENERVESOFTHEORBIT THEOPTICNERVECNII Func?on:Specialsensory-thespecialsenseofvision. Theop:cnervesarepaired,anteriorextensionsoftheforebrain (diencephalon)andarethereforeactuallyCNSfibertractsformedby axonsofre?nalganglioncells.Inotherwords,theyarethird-order neurons,withtheircellbodieslocatedinthere:na. CNIIbeginswheretheunmyelinatedaxonsofre:nalganglioncells piercethesclera(theopaquepartoftheexternalfibrouscoatofthe eyeball)andbecomemyelinated,deeptotheop:cdisc. Thenervepassesposteromediallyintheorbit,exi:ngthroughthe op:ccanaltoenterthemiddlecranialfossa,whereitformsthe op:cchiasm THENERVESOFTHEORBIT THEOPTICNERVECNII Intheop:cchiasm,fibersfromthenasal(medial)halfofeachre:na decussateinthechiasmandjoinuncrossedfibersfromthetemporal (lateral)halfofthere:natoformtheop?ctract. Thepar:alcrossingofop:cnervefibersinthechiasmisa requirementforbinocularvision,allowingdepth-of-fieldpercep:on (three-dimensionalvision). Mostfibersintheop:ctractsterminateinthelateralgeniculate bodiesofthethalamus.Fromthesenuclei,axonsarerelayedtothe visualcor:cesoftheoccipitallobesofthebrain. THENERVESOFTHEORBIT THEOCULOMOTORNERVECNIII CNIIIprovidesthefollowing • Motortothestriatedmuscleoffourofthesixextraocularmuscles (superior,medial,andinferiorrec:andinferioroblique)andsuperior eyelid. • Propriocep:vetothemuscleslistedabove. • Parasympathe:cthroughtheciliarygangliontothesmoothmuscleof thesphincterpupillae,whichcausesconstric:onofthepupilandciliary muscle,whichproducesaccommoda:on(allowingthelenstobecome morerounded)fornearvision. THENERVESOFTHEORBIT THEOCULOMOTORNERVECNIII CNIIIemergesfromthemidbrain,piercestheduramaterlateralto thesellardiaphragmroofingoverthehypophysis,andthenruns throughtheroofandlateralwallofthecavernoussinus. CNIIIleavesthecranialcavityandenterstheorbitthroughthe superiororbitalfissure. Withinthisfissure,CNIIIdividesintoasuperiordivision(which suppliesthesuperiorrectusandlevatorpalpebraesuperioris)andan inferiordivision(whichsuppliestheinferiorandmedialrectusand inferioroblique). Theinferiordivisionalsocarriespresynap:cparasympathe:c (visceralefferent)fiberstotheciliaryganglion. THENERVESOFTHEORBIT THEOCULOMOTORNERVECNIII CNIIIprovidesthefollowing • Motortothestriatedmuscleoffourofthesixextraocular muscles(superior,medial,andinferiorrec:andinferioroblique) andsuperioreyelid. • Propriocep?vetothemuscleslistedabove. • Parasympathe?cthroughtheciliarygangliontothesmooth muscleofthesphincterpupillae,whichcausesconstric:onofthe pupilandciliarymuscle,whichproducesaccommoda:on (allowingthelenstobecomemorerounded)fornearvision. THENERVESOFTHEORBIT THETROCHLEARNERVECNIV CNIVemergesfromtheposterior(dorsal)surfaceofthemidbrain(the onlycranialnervetodoso),passinganteriorlyaroundthebrainstem. Thetrochlearnervepiercestheduramateratthemarginofthe tentoriumcerebelliandpassesanteriorlyinthelateralwallofthe cavernoussinus. ThenCNIVcon:nuesthroughthesuperiororbitalfissureintothe orbit,whereitsuppliesthesuperiorobliquemuscles.
