系统解剖学 脑神经

CranialNervesLawsinmyclass:1.BeinghereINTIME.2.NODISSCUSIONinclass.QUESTIONMEOFFTHECLASSFORTHELACKOFTIMEINCLASSDivisionsofNervousSystemCentralnervoussystem

BrainSpinalcordPeripheralnervoussystemsympathetic

SpinalnervesSomaticnn.Motor

inponsCranialnervesVisceralnn.para-

(origin)

(destination)

SensoryinspinalcordNervoussystemcanbedividedintotwoanatomicalparts:thecentralnervoussystem(CNS)andtheperipheralnervoussystem(PNS).BodyTrunk&limbsHead&neckSomaVisceraSup.part:SomaVisceraInf.part:Soma:includingskeletalmuscleandskinetc.Viscera:includinggland,smoothmuscleandheart,alsohavesensationconveyandmovementcontrol,thelatteriscontrolledbysympathetiaandparasympatheticnervesSympatheticPara-Spinaln.Spinaln.Spinaln.Cranialn.Cranialn.Cranialn.Theboundaryisleftcolicflexure.Distribution?12pairsofcranialnervesattachtotheinferiorsurfaceofthebrainandpassthroughtheforamina,fissuresoftheskulltoinnervatestructuresinthehead,neck,andvisceralorgansofthetrunk.Thecranialnervesserveonlyheadandneckstructures.

exceptforthevagusnerve

(X),whichextendsintotheabdomen,Ofthe12pairsofcranialnerves,thefirsttwopairs

attachtotheforebrain,andtherestarisefromthebrainstem.Thecranialnervesare

numberedbyRomannumeralsfromIthroughXIIinsamedirection.TheRomannumeralsrefertotheorderinwhichthenervesarepositionedfromthefrontofthebraintotheback.Thenamesindicatethestructuresinnervatedortheprincipalfunctionsofthenerves.I,IIforebrainIII,IVmidbrainV,VI,VII,VIIIponsIX,X,XI,XIImedullaIOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.CharactersofnucleiSensoryMotorSomaticmotor:1.GenaralS.M.VisceralmotorSomaticsensoryVisceralsensory2.GenaralV.M.3.SpecialV.M.4.GenaralS.S.5.SpecialS.S.6.GenaralV.S.7.SpecialV.S.Nerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Nuclei:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

Nf(Axon)Charactersofnuclei1)Somaticmotor:movementoftougne&eyeball2)GenaralV.M.:glandsecretion&smoothmusclemove&heartbeat3)SpecialV.M.:movementofmusclesfrombranchialarches4)GenaralS.S.:senseoftouch&painfromskin5)SpecialS.S.

:senseofvision&hearing&equilibrium6)GenaralV.S.:likecarotidglomus7)SpecialV.S.

:tosmell&tasteNerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Neucli:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

NfGroupsofcranialnervesBasedonthetypesoffiberstheycontain,the12cranialnervesaredividedinto3functionalgroups.1.Purelysensorynerves(I,II,VIII)

—theycontainspecialsomaticfibersforsmell(I),vision(II),hearingandequilibrium(VIII)2.Primarilymotornerves(III,IV,VI,XI,XII)

—theycontainthesomaticmotorfiberstoskeletalmuscles,IIIalsocontainsparasympatheticfiberstosmoothmuscles3.Mixednerves(V,VII,IX,X)

—theycontainsomaticsensoryfiberstoface,

visceralsensoryfiberstomouth&viscera

somaticmotorfiberstoskeletalmuscles,

visceralmotorfiberstocardiac,smoothmusclesandglandsIII,VIIIX,Xcontainparasympatheticfiberstocardiac,smoothmusclesandglands.PurelySensoryCranialNerveOpticnerve(I)Olfactorynerve(II)Vestibulocochlearnerve(VIII)1.OlfactoryNerve(I)Olfactorynervefibersarisefromolfactoryreceptorcellslocatedinolfactorymucosaofnasalcavity,thengroupintobundlescalledfilamentsandpassthroughcribriformplate

ofethmoidbonetosynapseinolfactorybulb.Fibersofolfactorybulbneuronsextendposteriorlyas

olfactorytract,whichrunsbeneathfrontallobetoentercerebralhemispheresandterminatesinprimaryolfactorycortex.Fractureofethmoidbonemayresultinpartialortotallossofsmell,aconditionknownasanosmia.2.OpticNerve(II)Nervefibersthatarisefromretinaofeyeconvergeatthebackoftheeyeballtoformopticnerve,andenterthecranialcavitythroughthe

opticcanal.Thetwoopticnervesunitetoformtheoptic

chiasma.Medialhalffibersofthenervemakeacrossattheopticchiasmatotheoppositesideofthebrain,whereas

lateralhalffibersremainonthesamesideofthebrain.Theopticnervefiberspassposteriorlyfromtheopticchiasmatothethalamusviatheoptictracts.Inthethalamus,amajorityofthefiberterminatewithincertainthalamicnuclei.Thalamicfibersrun(astheopticradiation)tooccipital(visual)cortex,wherevisualinterpretationoccurs.Calcarine

Sulcus

Calcarine

Sulcus3.VestibulocochlearNerve(VIII)Thevestibulo-cochlearn.iscomposedoftwonervesthatarisewithintheinnerear.Nervefibersthatarisefromvestibularorgans(insemicircularcanalsandvestibule)form

vestibularnerve,whichisassociatedwithequilibrium.Nervefibersthatarisefromthespiralorgan(organofCorti)withinthecochleaformcochlearnerve,whichisassociatedwithhearing.thetwodivisionsmergetoformvestibulocochlearnerve.

Equilibrium—crista

ampullaris,maculautriculi,maculasacculiHearing—spiralorganofCortiThevestibulocochlearnervepassesthroughinternalacousticmeatustoenterbrainstematpons-medullaborder.Thevestibularnerveconveysimpulsesforsenseofequilibrium,andsensorynervecellbodiesarelocatedinvestibularganglia.Thecochlearnervetransmitsafferentimpulsesforsenseofhearing,andsensorynervecellbodiesarelocatedinspiralganglionwithincochlea.Fibersofcochlearnervesynapsewiththecochlearnucleiwithinthemedullaoblongata.Fromthere,fibersextendtothethalamusandsynapsewithneuronsthatconveytheimpulsestotheauditoryareasofthecerebralcortex.PrimarilyMotorCranialNerveOculomotorNerve(III)TrochlearNerve(IV)AbducensNerve(VI)AccessoryNerve(XI)HypoglossalNerve(XII)1.OculomotorNerve(III)Thenervearisesfromoculomotornucleus&Accessoryoculomotor

nucleusinthemidbrain.Itgoesthroughthesup.orbitalfissuretoeye.Itssomaticmotorfibersinnervatefourofthesixextrinsiceyemuscles

(inferiorobliqueandsuperior,inferior,andmedialrectusmuscles)thathelpdirecteyeball,andlevator

palpebrae

superiorismuscle,whichraisesuppereyelid.Inaddition,itsvisceralmotor(parasympathetic)fibersentertheeye-balltosupplythesphincterpupillaeoftheirisforpupilconstriction,andtotheciliarymuscleswithintheciliarybody,whichcontrolslensshapeforvisualfocusing.2.TrochlearNerve(IV)Thetrochlearnerveemergesfromdorsalmidbrainandcourseventrallyaroundmidbraintoenterorbitsthroughsuperiororbitalfissures.Itinnervatesthesuperiorobliquemuscle,whichcausetheeyeballtorotatedown-wardandawayfromthemidline(lateroinferiorly).3.AbducensNerve(VI)Theabducensnerveemergesfromthelowerportionoftheponsandenterorbitviasuperiororbitalfissuretoruntoeye.Itinnervatesthelateralrectusmuscle,whichmoveseyeballawayfromthemidlinelaterally.Lateralviewoftheorbit4.AccessoryNerve(XI)Theaccessorynerveisuniqueinthatitarisesfromboththebrainandthespinalcord.Thecranialroot

arisesfromnucleiwithinthemedullaoblongata(ambiguus

nucleus),passesthroughthejugularforamen,andinnervatestheskeletalmusclesofthesoftpalate,pharynx,andlarynx,whichcontractreflexivelyduringswallowing.Thespinalrootarisesfromthefirstfivesegmentsofthecervicalportionofthespinalcord,passesupwardthroughtheforamenmagnumtojoinwiththecranialroot,andthenpassesthroughthejugularforamen.Thespinalrootoftheaccessorynerveinnervatesthe

sternocleidomastoid

andthetrapezius

musclesthatmovethehead,neck,andshoulders.5.HypoglossalNerve(XII)Thehypoglossalnervearisesfromthehypoglossalnucleuswithinthemedullaoblongataandpassthroughthehypoglossalcanaloftheskulltoinnervateboththeextrinsicandintrinsicmusclesofthetongue.Motorimpulsesalongthesefibersaccountforthecoordinatedcontractionofthetonguemusclesthatisneededforsuchactivitiesasfoodmanipulation,swallowing,andspeech.MixedcranialNerveTrigeminalNerve(V)FacialNerve(VII)GlossopharyngealNerve(IX)VagusNerve(X)1.TrigeminalNerve(V)Thetrigeminalnerveisthelargestoneofcranialnervesandattachedtothe

anterolateralsideofthepons.Itconsistsof

sensoryandmotorroots.Thesensoryrootislargerthanthemotorroot.Cellbodiesofsensoryneuronsarelocatedinlargetrigeminal(alsocalled

semilunar)ganglion,locatedinabonydepressionontheinnersurfaceofthepetrouspartofthetemporalbone.Thesensoryfibersterminateinnucleiwithinthemidbrain,pons,andmedullaoblongata.Nerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Nuclei:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

Nf(Axon)Threebranchesarisefromthetrigeminalganglion.Theophthalmicnerveenterstheorbitthroughthesuperiororbitalfissure.Itconveyssensoryimpulsesfromskinofanteriorscalp,uppereyelid,nose,andfromnasalcavitymucosa,cornea,andlacrimalgland.Themaxillarynerveextendsthroughtheforamenrotundum.Itconveyssensoryimpulsesfromnasalcavitymucosa,palate,upperteeth,skinofcheek,upperlipandlowereyelid.Themandibularnervepassesthroughtheforamenovale.Itconveyssensoryimpulsesfromanteriortwo-thirdsofthetongue(excepttastebuds),lowerteeth,skinofchin,temporalregionofscalp.Thesmallermotorrootconsistsofmotorfibersofthetrigeminalnervethatoriginatefromthenucleiwithintheponsandaccompanythe

mandibularnervethroughtheforamenovaleandinnervatethemusclesofmasticationandcertainmusclesinthefloorofthemouth.Althoughthetrigeminalisamixednerve,itssensoryfunctionsaremuchmoreextensivethanitsmotorfunctions.2.FacialNerve(VII)Thefacialnerveissuesfrompons,justlateraltoabducensnerves,entertemporalboneviainternalacousticmeatus,andrunwithinthatbonebeforeemergingthrough

stylomastoidforamen;itthencoursestolateralaspectoffaceNerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Nuclei:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

Nf(Axon)Thefacialnervehasfivemajorbranchesonface:temporal,

zygomatic,buccal,

mandibular,and

cervical.Itssomaticmotorfibers

innervatethemusclesoffacialexpression,includingthescalpand

platysmamuscles.Itsvisceralmotor(parasympathetic)fiberssupplythelacrimalglands,nasalandpalatineglands,and

submandibularandsublingualglands.Someofthecellbodiesoftheseparasympatheticmotorneuronsarein

pterygopalatineand

submandibulorgangliaonthetrigeminalnerve.Itssensoryfibersconveysensoryimpulsesfromtastebudsofanteriortwo-thirdsoftongueandatinypatchofskinontheear;cellbodiesofthesesensoryneuronsareingeniculateganglion.3.Glosso-pharyngealNerve(IX)Theglossopharyngealnerveemergesfrommedullaandleaveskullviajugularforomentoruntothroat.Themotorfibersinnervatethemusclesofthepharynxandtheparotidglandtostimulatetheswallowingreflexandthesecretionofsaliva.Nerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Nuclei:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

Nf(Axon)Thesensoryfibersoftheglosso-pharyngealnervearisefromthepharyngealregion,theparotidgland,themiddle-earcavity,andthetastebudsontheposteriorone-thirdofthetongue,andfrompressurereceptorsofcarotidsinus(whichhelptoregulatebloodpressurebyprovidingfeedbackinformation),andfrom

chemoreceptorsinthecarotidbody(whichmonitorO2andCO2tensioninthebloodandhelpregulaterespiratoryrateanddepth).Sensoryneuroncellbodiesarelocatedinsuperiorandinferiorganglia.4.VagusNerve(X)Thevagusisthelongestofthecranialnerves.Itemergesfrommedullaoblongata,passthroughskullviajugularforamen,anddescendthroughneckregionintothoraxandabdomen.Itsvisceralmotor(parasympathetic)

fibersarisesfromthedorsalmotornucleusofthevagus,andinnervatethepharynx,larynx,respiratorytract,lungs,heart,andesophagus,andthoseoftheabdominalviscera,withtheexceptionofthelowerportionofthelargeintestine,andareinvolvedinregulationofheartrate,breathing,anddigestivesystemactivity.Nerves:IOlfactoryn.IIOpticn.IIIOculomotorn.IVTrochlearn.VTrigeminaln.VIAbducensn.VIIFacialn.VIIIVestibulocochlearn.IXGlossopharyngealn.XVagusn.XIAccessoryn.XIIHypoglossaln.Nuclei:Oculomotornucleus./Trochleal

nucleus./Abducent

nucleus/Hypoglossal

nucleus.Motornucleusoftrigeminaln./Nucleusoffacialn./Nucleusambiguous/AccessorynucleusAccessoryoculomotornucleus/Dorsalnucleusofvagusn./Sup.salivatorynucleus(VII)/Inf.salivatorynucleus(IX)Nucleusofsolitarytract(IX、X、XI)Spinalnucleus(V、VII、IX、X)/Pontinenucleus/Mesencephalicnucleusoftrigeminaln.Cochlearnucleus/Vestibularnucleus

Nf(Axon)4.VagusNerve(X)Itssomaticmotorfibers

arisefromthenucleus

ambiguusandserveskeletalmusclesofpharynxandlarynx(involvedinswallowingandspeech)viaitsbranches—thesuperiorlaryngealnerveandtherecurrentlaryngealnerve.VisceralNervousSystemWhatisvisceralnervoussystem?Structurally,peripheralnervoussystemcanbeclassifiedinto

thespinalnerves,whichattachtothespinalcord,andthecranialnerves,whichattachtothebrain.Functionally,peripheralnervoussystemisdividedintothe

somaticnerve(somaticsensorynerveandsomaticmotornerve),andvisceralnerve(visceralsensorynerveandvisceralmotornerve).SomaticNervousSystemThesomaticsomaticnervesuppliesskin,limbsandbodywall,conveyssomaticsensoryinformation(pain,temperature,touch,pressureandproprioception,smell,vision,hearingandequilibrium)tothebrain.

Thesomaticmotornerveinnervatesskeletalmuscles,andcontrolscontractionofskeletalmuscles.Bycontrollingcontractionoftheskeletalmuscles,itregulatesposture,balanceandvoluntarymovementsofthebody.

VisceralNervousSystemThevisceralsomaticnervesuppliesviscera,heart,bloodvesselsandglands,andconductsvisceralsensoryinformation(pain,temperature,stretch,

nausea,hunger,taste,chemicalandphysicalchanges)

tothebrain.Bycontrollingtheseeffectors,itregulatessuchvisceralfunctionsasheartrate,bloodpressure,digestion,andurination,whichareessentialformaintainingthestabilityofthebody’sinternalenvironment.

Thevisceralmotornerveinnervatescardiac,smoothmusclesandglands,andcontrolsinvoluntarycontractionofcardiacandsmoothmusclesandsecretionofglands.So,itcontinuouslymonitorstheactivitiesofthevisceralorganssothatthevisceralmotorneuronscanmakeadjustmentsasnecessarytoensureoptimalperformanceofvisceralfunctions.

PNS(cranialnervesandspinalnerves)SomaticNerveSomaticSensoryNerveSomaticMotorNerveVisceralNerveVisceraSensoryNerveVisceralMotorNerveskin,limbs,bodywall,eyeball,innerear,nosepain,temperature,touch,pressure,proprioception,smell,vision,hearingandequilibrium.Skeletalmusclesviscera,heart,bloodvesselsandglandspain,temperature,stretch,

nausea,hunger,taste,chemicalandphysicalchangescardiac,smoothmusclesandglandsBoththecranialnerves,whichattachtothebrain,andthespinalnerves,whichattachtothespinalcord,containsomaticandvisceralnervefibers.Inotherwords,thevisceralnerve(sensoryandmotor)attachestobothbrainandspinalcord.Asaresult,thevisceralnervoussystemiscomposedofvisceralsensorynerveandvisceralmotornerve,whichattachtothebrainandspinalcord,

andinnervatesviscera,heart,bloodvesselsandglands.VisceralNervousSystemVisceralSensoryVisceralMotorViscera,Heart,BloodVessels,GlandsCardiacmusclesSmoothmusclesGlandsPain,Temperature,Stretch,

ChemicalandPhysicalChanges,Nausea,Hunger,TasteVisceralMotorNervousSystemAutonomicNervousSystem(ANS)VegetativeNervousSystemThefunctionsoftheorgansinnervatedbyvisceralmotornervoussystemarenotusuallyundervoluntarycontrol.Theorgansinnervatedbyvisceralmotornervoussystem(viscera,heart,bloodvessels,gland)areconcernedwithmetabolism,whichiscommonlifefeaturesofanimalsandplants.1.VisceralMotorNervousSystemDivisionsofANSSympatheticDivisionParasympatheticDivisionDivisionsofANSTheANShastwodivisions,thesympathetic

and

parasympatheticdivisions.Bothsympathetic

andparasympathetic

divisions

consistofchainsoftwomotorneurons.Thefirstofthesemotorneuronsiscalledthe

preganglionicneuron,

thecellbodyofwhichlieswithinthespinalcordorbrain.Theaxonofthepreganglionic

neuroniscalledthe

preganglionicfiber

andsynapseswiththesecondmotorneuron.Thesecondmotorneuroniscalledthepostganglionicneuron,inaperipheralganglion.Itsaxoniscalledthepostganglionicfiberandextendstothevisceralorgans.However,thespecificoriginofthepreganglionicneuronsandthelocationofthegangliadifferinthetwosubdivisionsoftheANS.Functionally,the

preganglionic

neuronsignalsthepostganglionicganglion,whichthenstimulatescontractionofthecardiacandsmoothmusclesandsecretionofglands.Preganglionicfifersarethinmyelinated

fibers,whereaspostganglionicfibersareeventhinnerandunmyelinated.Consequently,theconductionofimpulsesthroughtheANSisslowerthanconductionthroughthesomaticmotorsystem.Itisimportanttoemphasizethattheautonomicgangliaaremotorgangliacontainingthecellbodiesofmotorneurons.Theyarenotsensoryganglia,likethedorsalrootganglia.

(1)SympatheticDivisionA.PreganglionicNeuronsThepreganglionicneuronbodiesofthesympatheticdivisionarelocatedwithinthespinalsegmentsofthefirstthoracic(TI)tothesecondlumbar(L2)levels,wheretheyformthelateralgrayhorn.B.PostganglionicNeuronsThepostganglionicneuronbodiesliewithinthe

paravertebral

ganglia

(sympathetictrunkganglia)andthe

prevertebral

ganglia.Theparavertebralgangliaformachainofganglia,whichiscalledthesympathetictrunk.Thesympathetictrunkislocatedoneithersideofthevertebralcolumnandextendsfromthenecktothepelvis.CervicalSympatheticGangliaThereisapproximatelyonesympathetictrunkganglionforeachspinalnerve.Note,however,thatthenumberofsympathetictrunkgangliaandspinalnervesisnotidentical,becausesomeadjacentgangliafuseduringdevelopment.Suchfusionismostevidentintheneckregion,wherethereareeightspinalnervesbutonlythreesympathetictrunkganglia:thesuperior,middleandinferiorcervicalganglia.Furthermore,theinferiorcervicalganglionusuallyfuseswiththefirstthoracicgangliontoformthestellateganglioninthesuperiorthorax.ThoracicSympatheticGangliaLumbarandSacralSympatheticGangliaTheprevertebralganglialieanteriortothevertebralcolumn,includingtheceliac,superiormesenteric,inferiormesentericandinferior

hypogastric

ganglia.PrevertebralSympatheticGangliaThepreganglionic

sympatheticneuronssend

preganglionic

sympatheticfibersthroughtheadjacentventralrootintothecorrespondingspinalnerves.Then,each

preganglionic

fiberexitsthecorrespondingspinalnervetoenterthesympathetictrunkganglion.Fromthere,thepreganglionicfibersynapseswiththepostganglionicneurons,eitherwithinasympatheticganglionorinaprevertebral

ganglion.Finally,thepostganglionicfiberextenddirectlybacktothespinalnervesandtraveldistallywithinthespinalnerves,toinnervatethevisceralorgans,orinnervatesdirectlytothevisceralorganswithoutbacktothespinalcord.Inmanycases,the

preganglionicfiberascendsordescendsinthesympathetictrunkbeforesynapsing;thisallowssympatheticoutputs,whichcomeonlyfromthethoracolumbarregionofthespinalcord,tosupplythesuperiorandinferiorbodyregions,suchasthehead,neckandpelvis.Thepartofthepreganglionicfiberbetweenthespinalcordandthesympathetictrunkiscalledthewhiteramus

communicans

becausethe

preganglionicfiberismyelinated.Thepartofthepostganglionicfiberbetweenthespinalcordandthesympathetictrunkiscalledthegary

ramus

communicans

becausethe

postganglionicfiberisunmyelinated.(2)ParasympatheticDivisionTheparasympatheticdivisionisalsocalledthecraniosacraldivisionoftheANS.Thisisbecauseits

preganglionicneuronsoriginateinthebrainandinthesecondthroughfourthsacralsegments(S2-S4)ofthespinalcord.A.PreganglionicneuronsThepreganglionic

neuronbodiesofthepar