autonomic nervous system (ans) - class syllabus€¦ · autonomic nervous system (control over the...
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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: