AutonomicNervousSystem(ANS)ControlsInvoluntaryActions

Bio230Dr.CarlaSweetM.D,

ANSworkscloselywiththeHypothalamus

VISCERALMOTOR

HowtheNervousSystemisorganized.

*ANS

AnatomicalDivisions

ß-FunctionalDivision--à

*ANSRegulatesunconscious processesthatmaintainhomeostasis-bloodpressure,bodytemperature,respiratoryairflowetc.

*ANScarriesoutitsactionswithoutourconsciouscontrol(automatically).

AutonomicNervousSystem(ANS)

WhatistheANS?TheANSistheVISCERALMOTORmotordivisionofthePeripheralNervousSystem(PNS)Youmustknowwhat“visceral”means.1.Thosestructures/organsthatareintheVentralBodyCavities:-ThoracicCavity(heartandlungs)-AbdominalPelvicCavity(Liver,gallbladder,stomach.stomach.spleen,intestines,pancreas,kidney,bladderandthereproductiveorgans).

2.ANSregulatesthesmoothmuscle,cardiacmuscleandglandsthroughoutthebody.ANSregulatesarteriolebloodvessels(dilatationorconstriction)alsobecauseof

thesmoothmuscleinthewallsofthearterioles.

ThisisincontrasttotheSOMATICMOTOR:- Somaticdealswithalltheskeletalmusclesofthebody.SomaticMotormuchsimpler!

Remember:Somaticmotorsystem(Toskeletalmuscles):

-OnemotorneuronextendsfromtheCNStoskeletalmuscle-Axonsarewellmyelinated,conductimpulsesrapidly

BycontrasttheVisceralMotorSystem:Autonomicnervoussystem(ControlovertheANSisforthemostpartinvoluntary.)

Hasachainoftwomotorneurons1. First=Preganglionicneuron(thecellbodyliesintheCNS)myelinated fibers.2.Second=Postganglionicneuron(thecellbodyliesinthePNSinanperipheralautonomicganglion(rememberwhatganglionmeans)fibershereareunmyelinated.

SomaticMotorvs.VisceralMotor

TheAutonomicandSomaticMotorNervousSystems

ANS=chainof2motorneurons:Preganglionicaxonsarethin,lightlymyelinated.Preganglionic cellbodyliesinlateralhornofspinalcord.Postganglionicaxonsarethinner&unmyelinated

Somatic=1motorneuronwhichtypicallyhasthickaxons,heavilymyelinatedMotorcellbodyresidesinanteriorhornofspinalcord.

Besureyoucanfollowthe2differentpathwaysshownabove.Bothpathwayssharetheventralrootandspinalnerveforinitialdistribution.

lateralhorn

anteriorhorn

DivisionsoftheANS

1.)SympatheticDivision:“FightorFlight”-activeduringexercise,excitementoremergencies-innervatesallvisceralorgansinthebody-alsoinnervatesthesweatglandsandarrectorpilimusclesoftheskin-innervatesthesmoothmusclesinbloodvessels(causesvasodilatationorcontraction)

2.)ParasympatheticDivision:“Rest&Digest”-activewhenbodyisrelaxed-conservesenergy-performs“housekeeping”activitieslikedigestion,eliminationofwaste(feces/urine)- doesnotinnervatetheskin,orsmoothmusclesinbloodvessels

Thegoalistokeepabalancebetweenthesetwodivisionsduringourdailylives.

AnatomicalDifferencesbetweenSympatheticandParasympathetic1.OriginatefromdifferentregionsoftheCNS:

a.SympatheticDivision(AKAThoracolumbarDivision)- itsfibersemergefromthethoracicandsuperiorlumbarpartsofthespinalcord(T1-L2)

b.ParasympatheticDivision(AKACraniosacralDivision)- itsfibersemergefromthebrain(cranialnervesIII, VII,IXandX)andthesacralpartofspinalcord(S2-S4)

2.) Locationofganglia:a.Sympathetic- ganglialienearspinalcordandvertebralcolumnb.Parasympathetic– ganglialiefarfromCNS,lieinorneartheorgansinnervated

3.)Relativelengthofpre- andpostganglionicfibers:a.Sympathetic- sincegangliaareclosetothespinalcord,

thepreganglionicfibersareshortandpostganglionicarelongb.Parasympathetic- sincegangliaarefarfromCNS,

thepreganglionicfibersarelong,postganglionicshort

4.Neurotransmittersreleasedatsynapses:a.Sympathetic:allpreganglionicfibersreleaseacetylcholine(ACh)

-mostpostganglionicfibersreleasenorepinephrine (akanoradrenaline)=“Adrenergic”fibersb.Parasymapthetic:allpreandpostganglionicfibersreleaseACh=“Cholinergic”fibers

AnatomicalDifferencesbetweenSympatheticandParasympatheticcontinued:

Sympathetic

Parasympathetic

AnatomicalDifferencesbetweenSympatheticandParasympatheticcontinued:

5.Branchingofaxonsa. Sympatheticaxons– highlybranched=Influencesmanyorgans

-eachneuroninfluencesalargernumberofvisceralorganstomobilizeatthesametimefor“fightorflight”.Theirinfogoes“viral”.

SYMPATHETICmeans“experiencetogether”.Thisreflectsthebodywidemobilizationb.Parasympatheticaxons– fewtonobranches=Localizedeffect

-withlittletonobranchingeffectsaremorelocalizedanddiscrete(verydiscrete!)

Sympathetic

Parasympathetic

norephinephrine(noradrenaline)

NE

ACh

ACh

SympatheticDivisionofANS- (Thoracolumbar Division)T1-L2

-TheSympatheticDivisionismuchmorecomplex,inpartduetoit’sbranching.

-Innervatesallthevisceralorgansofthebody(liketheParasympathetic),butalsoinnervatesthesmoothmusclesofbloodvessels,structuresofsuperficialbodyregions(sweatglands,arrector pili musclesintheskin)andinnervatestheadrenalgland.

-thesympatheticdivisioncontainsmoregangliathantheparasympathetic.Soundsconfusingbutifwetakeitstepbystepyouwillgetit!

Letsstartwithwhatweknow:Sympatheticpreganglionic neuroncellbodiesarehousedintheLATERALHORNoftheT1–L2ONLY!Preganglionic sympatheticaxons:travelwithsomaticmotorneuronaxonsand

exitthespinalcord,enterfirsttheventralrootsthentheT1–L2spinalnerves.SofarmuchlikeMotorNeurons.

Preganglionic sympatheticaxonsremainwithinthespinalnerveforashortdistance,theythenbranchoffandleavethespinalnerveviathewhiteramuscommunicans.TheentranceintotheSympathetictrunk(akaChain).

TogettotheSympatheticNervousSystemMUSTtaketheSympatheticChainTrain.LeavingonplatformslocatedT1throughL2.

Sympathetic(Thorocolumbar)NervousSystemCalledtheThorocolumbar becausethecellbodiesofthepreganglionic neuronsarelocatedinthelateralhornsofthespinalcordofsegmentsT1-L2

ThecellbodiesofthePOSTGANGLIONICNEURONScanbefoundintwodifferentplaces:1.PARAVERTEBRAL GANGLIA(AKASYMPATHETICCHAINGANGLIA)para=alongtheside,thischainisfoundonboththeleftandrightsideofthevertebralcolumn2.PREVERTEBRAL GANGLIA.Pre=infrontof.Thesegangliaareinfrontofthevertebralcolumn,theyareactuallylocatedontheabdominalaorta,hangingaroundthemajorbloodvesselsoftheabdominalaorta,liketheceliactrunk,superiormessenteric andinferiormessenteric.

Letsstartwiththeparavertebral ganglia=thesympatheticchainganglia

1.

2.

SympatheticDivision– TheParavertebral (akasympatheticchain)Ganglia-foundinthesympatheticchain)CalledtheParavertebral becausethesepostganglionic cellbodiesliebesidethevertebrae.

ThesepinkchainsarecalledtheSYMPATHETICCHAINganglia(akaparavertebral ganglia).Looklikepearlsonanecklace!

-Consistsofarightandleftsympatheticchains(akatrunks)-Thesesympatheticchainslienexttothevertebralcolumn,andrunessentiallytheentirelengthofthevertebralcolumn.

CanonlygettothesympatheticChainviathewhiterami (rami pluraloframuswhichisthesingular).Thesewhiterami ONLYfoundatthelevelsofT1-L2.Onceyouareinthesympatheticchainyoucangouptothecervicalregionordowntothesacralregion.Youareinthechain!Youraccesstothesympatheticnervoussystem!

SympatheticNScontinued:

Howthesympatheticchainlooks.Besuretounderstandthisdiagram.Rememberthewhiterami arethesecondofframpofthespinalnerve.

WHITERAMI:onlylocatedT1-L2.Theonlywaytogettothesympatheticchain.

Theseuniversaltruthsmustberemembered:-Whiterami communicanes onlyexisttoconnectT1toL2ventral rami tothesympatheticchain. Called“white”becausethepreganglionic axonsthatenteraremyelinated (whiteincolor).

-Grayrami communicanes existatALL 31spinalnervelevels.EVERY spinalnerveisconnectedtothesympatheticchainbyagrayramus,whichcarriespostganglionic(postsynaptic)sympatheticfiberstotheVentralordorsalRami.Theyarecalled“Gray”becausethesepostganglionicfibers(axons)areunmyelinated.

-Thesympatheticchainexiststocarrysomeofthepreganglionic (presynaptic)fibersfromtheT1-L2levelsuptotheneckandheadanddownintothelowerabdomenandpelvis.

Ifyoufindinnerpeacewiththeseuniversaltruths,thenyouhavepassedthefirststeponyourjourneytobecomeanSympatheticAutonomicMaster.

SowhatarethepossiblepathwaysoncewehavearrivedintotheSympatheticChain?

Oncethepreganglionic sympatheticfibershavearrivedinthesympatheticchaintheydooneoffourPathways:

1. SpinalNervePathway-toskinstrictures:Thepreganglionic neuronfibermaysynapseimmediatelyinthesympatheticchainganglionlocatedatthelevelitentered.Thepostganglionic neuronfiberthenleavesthechainatthelevelitentered,viathegrayramus toenterbackintothespinalnerve.

1a.Thepreganglionic neuronfibermayascendordescendinthesympathetictrunkbeforesynapsing inasympatheticchainganglionlocatedatadifferentspinalcordlevel.Itmaythenexitviathegrayramus atthatlevelandenterbackintothespinalnerve.

2. SympatheticOrganNervePathwaytothoraciccavitystructures:The preganglionicneuronfibermaysynapseimmediatelyinthesympatheticchainganglionitenteredoritmayascendordescendinthesympathetictrunkbeforesynapsing inasympatheticchainganglionlocatedatadifferentspinalcordlevel.Thepostganglionicfiberthenexitsthesymapthetic chainviaan“organ”nervetoinnervateatargetthoracicorgan.Heart,lung,esophagus,bloodvesselsofthoraciccavity.

3. Splanchnic NervePathwaytoabdominalcavitystructures:Thepreganglionic neuronfiberpassesthroughthesympatheticchaingangliawithoutsynapsing atall,synapsing insteadinaprevertebral ganglion.Reachestheprevertebral gangliaviaaSplanchnic Nerve.

4.AdrenalMedullaPathway:Thepreganglionic neuronfiberpassesthroughthesympatheticchaingangliawithoutsynapsing atall,travelstoaprevertebral ganglion,againnotsynapsing,andtravelsdirectlytotheAdrenalGlandMedulla.Thispathwayistheexceptiontothe2motorneuronrulefortheANS.

Ingeneral,sympatheticinnervation to allskinstructuresfollowspathways1and1a.Sympatheticinnervation totheorgansofthethoraciccavityfollowpath2Sympatheticinnervation tointernalorgansintheabdomenandpelvisfollowsthethird pathway,primarily.

Letslookateachpathway!

1. Thepreganglionic neuronfibermaysynapseimmediatelyinthesympatheticchainganglionlocatedatthelevelitentered.Thepostganglionic neuronfiberthenleavesthechainatthelevelitentered,viathegrayramus toenterbackintothespinalnerve.

ThediagramshowsT10sympatheticspinalnerveinnervation areastotheskin.Eachspinalnervesuppliesdiscreteareasoftheskin.ThesmallerblueareasshowjustT10spinalnerveareas,whereasthelargerblueareaonthediagramrepresentsthesympathetic

distributionofallspinalnervesegmentstogetherT1-L2

Pathway#1toskinstructuresviaspinalnerves(ventralanddorsalrami)

Skinstructures:1. sweatglands2. arrector pillmuscles3. bloodvesselstoskinalsotobloodvesselssupplyingskeletalmuscles

preganglionic fibersmyelinated,shownassolidlinespostsynapticfibersunmyelinatedshownasdashes-------

Pathway#1a.Thepreganglionic neuronfibermayascendordescendinthesympathetictrunkbeforesynapsing inasympatheticchainganglionlocatedatadifferentspinalcordlevel.Itmaythenexitviathegrayramus atthatlevelandenterbackintothespinalnerve.ThisishowyougetsympatheticflowtoareasaboveT1andbelowL2.

Review-sympatheticpathwaytoskin-synapseinsympatheticchainganglia,leavethrugrayrami,returntoventralrami andleavethroughspinalnerves.

preganglionic fibersmyelinated,shownassolidlinespostsynapticfibersunmyelinated shownasdashes-------

Pathway2diagramtothoracicorgans:Synapseoccursinsympatheticchainganglia,theyDONOTexitintothegrayrami communicans,butexitoutviaan“organnerve”.Thisshowsapostganglionic(postsynaptic)fiberleavingthechainatthelevelitenteredtotraveltothelung,andapreganglionic fiberascendingtosynapseatahigherlevel,wherethepostganglionicfibersthenleavesandtravelstotheheart.These“organ”nervesDONOTexitoutaspinalnerve.

Pathway3:Splanchnic NervePathwayThepreganglionic neuronfiberspassthroughthesympatheticchainganglionwithoutsynapsing atall,synapsing

insteadinaprevertebral ganglion.Travelstotheprevertebral ganglionviaaSPLACHNICNERVE.Thisisthepathwaytotheabominal &pelvicorgans.

Aboveiswheretheprevertebral ganglionarelocated(ontheabdominalaorta).Theyareunpaired.-Occuronlyinabdomenandpelvis(originatefromT5-L2region)-Lieanteriortothevertebralcolumn- hencenameprevertebral.-Mainprevertebral ganglia(don’tneedtoknowthese,justsoyoucanlocatethemonthediagramandunderstandwheretheyareinrelationshiptothesympatheticchainwhichisalsoshowinthediagram).

Celiac,superiormesenteric,andinferiormesenteric,ganglia

Thoracicsplanchnic nervesleadingdowntoprevertebral (collateral)ganglia.

Pathway#3- anotherviewforyou

Synapseoccursintheprevertebral ganglia.Preganglionic fibersbypassthesympatheticchainganglia.Usesasplanchnic nervetp traveltoits“hookup”intheprevertebralganglia.

eye-pupildilationskin-vasoconstrition,increasesweatproduction,piloerection.salivaryglands-decreasesecretions

heart- increaseheartratelungs- bronchialdilationliver-breakdownofstoredglycogen=releaseofglucosegallbladder- relaxesstomach- decreasemotilityglandsofstomachinhibited

adrenalgland-secretionofepinephrinekidney- decreasebloodflow;decreaseurineformation

intestines- decreasemotilityrectum- tightensinternalsphincter

bladder- relaxes,tightensinternalsphincter

extgenitalia- ejaculation

ActionsoftheSympatheticN.S.(comparetoparasympathetic)

____preganglionic --------postganglionic

prevertebral gangliainfrontofaorta

PuttingitalltogetherSympatheticN.S.

Pathway1:toskinstructuresviaspinalnerves.Synapseoccursinparavertebral(sympatheticchain)ganglia Pathway2:tothoracicorgansviaOrganNerve.

Synapseoccursinparavertebral (sympatheticchain)ganglia

ê splanchnic nervePathway3:topelvicorgansviasplanchnic nerve.Synapseoccursinprevertebral ganglia.

Pathway4- AdrenalMedulla-notshownUsessplanchnic nervetoreachadrenalgland.Goesthroughprevertebral ganglia,doesnotsynapsethere,insteadtravelsdirectlytoadrenalmedulla.

çorgan nerve

ê

solidlines=presynaptic (preganglionic)myelinated fibers.dashedlined=postsynaptic(postganglionic)nonmyelinated fibersNEUROTRANSMITTERS:presynaptic fibersreleaseacetylcholine(ACh),postsynapticfibersreleasenorepinephrine (NE)

ParasympatheticDivision– (Craniosacral Division)

cranialoutflowfromcranialnerves:III– oculomotor =constrictspupilsVII-facial=increasesecretionslacrimal andsalivaryglandsIX-glosspharyngeal=increasesalivaryglandsecretionTheabovehave“terminalganglia”,synapseclosetotarget.Therest(below)have”intramuralganglia”,synapsesintargetorgan.X- Vagus “thewanderer”- thisnerveisextremelyimportant!Containsnearly80-90%ofthepreganglionic

parasympatheticfibersinthebody.Innervatesthevisceralorgansofthethoraxandmostoftheabdominalorgans.Heart-slowsheartdownLungs-constrictsbronchi&increasesbronchialsecretionsDigestivetract- stimulatesperistalsis&secretionofdigestivejuicesLiver&gallbladder- promotesglycogenformation;secretion ofbile

Scaral OutflowfromsegmentsS2-S4ofthespinalcord-continueswherethevagus leftoff.Innervatesthelowerlargebowelsegmentandtherectum.Contractsretcumandrelaxesinternalanalsphinctertocausedefication.-Urinarytract-contractsbladdermuscle&relaxesinternalurethralsphinctertocauseurination.Genitalsystem-producesengorgement(erection)oferectiletissue.Sacraloutflowtravelswithspinalnervesofregion.

(noticelongpreganglionic andshortpostganglionicfibers)Fromvagus tosacraloutlow,theganglialieintheorgantheyinnervate(calledINTRAMURALGANGLIA).CN’s lll,Vll,IX ganglialieclosetotargetorgan(calledTERMINALGANGLIA).

Oneotherlookattheparasympatheticsystem.Thisoneisnicebecausetheintramuralgangliaarecircled.Hereyoucaneasilyseehowlongthepresynapticfibersareandjusthowshortthepostsynapticfibersare.

Asyouarelookingattheorganshere,gothroughtheactionstheparasympatheticsystemwillhaveoneachoftheseorgans.Ifyouknowthefunctionoftheparasympatheticsystemyoushouldbeabletofiguretheaffectsontheseorgans.

nervegasesthatinhibitthebreakdownofACHproducestheDUMBELSsyndrome:Diarrhea,urination,miosis(constrictedpupils),bradycardia(slowheartrate)andbronchorrhea (waterysputum),emesis(vomiting),lacrimation,salivation.

Parasympatheticpreganglionic fibersreleaseacetylcholine(ACh).postganglionicfiversreleaseACh alsoattheeffector (target)ogran.

AnotherParasympatheticview.

Whattonote:Nocomplicatedchaintogetonoroff.Astraightforward,2viseral motorneuronpathway.Thepreganglionic fibersarelong!Theganglia(terminalganglia)theysynapsewithareveryclosetotheorganstheyinnervateinthehead(CN’Slll,Vll,andlX)whileinthethoracicandabdominal/pelvicorganstheyactuallyareintheorganthemselves(intramuralganglia)!

Neurotransmitters:preganglionic fibersreleaseAcetylcholine(ACh)postsynapticfibersreleaseACh

Forthelecturepartoftheexamyouwillbegivenoneofthese4pathwaystodraw.Youwillbesuppliedwiththeblankdrawingthatweusedinclassforthesepathways.Youwillberequiredtolabelallthestructuresthepathwaypassesthrough,whatneurotransmitter(s)arereleased,andtheactiononthetargetorganIgiveyou.(example,actiononheart=speedsupheartrate).Practice,youhavetheblankdiagramspostedonyourwebsiteworksheets.

Theeffectsoftheparasympatheticsystemareverylocalizedtothatorganittargets.Incontrast,thesympatheticsystemhasmuchmorewidespreadeffects,especiallyiftheadrenalglandreleasesitsepinephrine“adrenaline”intothebloodstream…thenthewholebodyisactivated!Remembersympatheticmeans“alltogether”.Inthiscaseallyourbodyisworkingtogethertogetyououtofadangeroussituation.

Onelastthing: