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THEBACK THESPINALCORD THESPINALCORD Thestructuresinthevertebralcanal: • thespinalcord • spinalnerveroots • spinalmeninges • theneurovascularstructures THESPINALCORD Thespinalcordoccupies thesuperior2/3ofthevertebralcanal THESPINALCORD Inadults,thespinalcordis42–45cmlong ItisconHnuouscraniallywiththemedullaoblongata,justbelowthe leveloftheforamenmagnum,attheupperborderoftheatlas. Itterminatescaudallyastheconusmedullaris. AtthelevelofthediscbetweenvertebraeLIandLIIinadults. ItcanendashighasvertebraTXIIoraslowasthediscbetween vertebraeLIIandLIII Thelumbarandsacralnerverootsarethelongest,extendingfar beyondtheterminaHonoftheadultspinalcordatapproximatelythe L2leveltoreachtheremaininglumbar,sacral,andcoccygealIV foramina. THESPINALCORD TheterminaHonofthespinalcord-thecaudaequina. Inneonates,thespinalcordextendsapproximatelytovertebraLIIIbut canreachaslowasvertebraLIV. Growsmuchmoreslowlythanthebonyvertebralcolumnduringfetal development. Thedistalendofthecord,theconusmedullarisisconeshaped. THESPINALCORD Thespinalcordisnotuniformindiameteralongitslength. Ithastwomajorenlargementsinregionsassociatedwiththeorigin ofspinalnervesthatinnervatetheupperandlowerlimbs. • cervicalenlargement • lumbosacralenlargement Acervicalenlargementoccursintheregionassociatedwiththe originsofspinalnervesC4toT1,whichinnervatetheupperlimbs. Alumbosacralenlargementoccursintheregionassociatedwiththe originsofspinalnervesT11toS1,whichinnervatethelowerlimbs. THESPINALCORD Theanteriorramiofthespinalnervesarisingfromthisenlargement makeupthe: • lumbarplexuses • sacralplexuses ofnervesthatinnervatethelowerlimbs. THESPINALCORD Theexternalsurfaceofthespinalcordismarkedbyanumberof fissuresandsulci: • Theanteriormedianfissureextendsthelengthoftheanterior surface. • Theposteriormediansulcusextendsalongtheposteriorsurface. • Theposterolateralsulcusoneachsideoftheposteriorsurface markswheretheposteriorrootletsofspinalnervesenterthecord. THESPINALCORD Internally,thecordhasasmallcentralcanalsurroundedbygrayand whitemaSer: • ThegraymaRerisrichinnervecellbodies,whichform longitudinalcolumnsalongthecord,andincrosssecHonthese columnsformacharacterisHcH-shapedappearanceinthecentral regionsofthecord. • ThewhitemaRersurroundsthegraymaSerandisrichinnervecell processes,whichformlargebundlesortractsthatascendand descendinthecordtootherspinalcordlevelsorcarryinformaHon toandfromthebrain. THESPINALNERVES THESPINALCORD Thespinalnervesconsistof31pairsofnerves: • 8cervical(1stbetweenskullandC1) • 12thoracic • 5lumbar • 5sacral • 1coccygeal ThefirstcervicalC1nerveslackdorsalroots in50%ofpeople. Thecoccygealnervemaybeabsent. THESPINALCORD SpinalnervesiniHallyarisefromthespinalcordasrootlets-the rootletsconvergetoformtwonerveroots SpinalnervesiniHallyarisefromthespinalcordasrootlets-the rootletsconvergetoformtwonerveroots: • anterior(ventral)nerveroot • posterior(dorsal)nerveroot THESPINALCORD Ananterior(ventral)nerveroot,consisHngofmotor(efferent)fibers passingfromnervecellbodiesintheanteriorhornofspinalcordgray maSertoeffectororganslocatedperipherally. Aposterior(dorsal)nerveroot,consisHngofsensory(afferent)fibers fromcellbodiesinthespinal(sensory)orposterior(dorsal)root ganglion(DRG)thatextendperipherallytosensoryendingsand centrallytotheposteriorhornofspinalcordgraymaSer. THESPINALCORD Theposteriorandanteriornerverootsunite,withinorjustproximal totheintervertebralforamen,toformamixed(both motorandsensory)spinalnerve. Thespinalnerveimmediatelydividesintotworami: • posterior(dorsal)ramus • anterior(ventral)ramus THESPINALCORD Thespinalnerve,theposteriorandanteriorramicarrybothmotor andsensoryfibers. ThetermsmotornerveandsensorynervearealmostalwaysrelaHve terms. Nervessupplyingmusclesofthetrunkorlimbs(motornerves)also containabout40%sensoryfibers,whichconveypainand propriocepHveinformaHon. Thecutaneous(sensory)nervescontainmotorfibers,whichserve sweatglandsandthesmoothmuscleofbloodvesselsandhair follicles. THESPINALCORD Theunilateralareaofskininnervatedbythesensoryfibersofasingle spinalnerveiscalledadermatome. TheunilateralmusclemassreceivinginnervaHonfromthefibers conveyedbyasinglespinalnerveisamyotome. THESPINALCORD Astheyemergefromtheintervertebralforamina,spinalnervesare dividedintotworami: • posterior(primary)ramiofspinalnerves • anterior(primary)ramiofspinalnerves Posterior(primary)ramiofspinalnervessupplynervefiberstothe: • synovialjointsofthevertebralcolumn, • deepmusclesoftheback, • overlyingskininasegmentalpaSern. Posterior(primary)ramiofspinalnervesremainseparatefromeach other(donotmergetoformmajorsomaHcnerveplexuses). THESPINALCORD Anterior(primary)ramiofspinalnervessupplynervefiberstothe muchlargerremainingarea,consisHngoftheanteriorandlateral regionsofthetrunkandtheupperandlowerlimbs. Anterior(primary)ramiofspinalnervesaredistributedexclusivelyto thetrunkgenerallyremainseparatefromeachother,alsoinnervaHng musclesandskininasegmentalpaSern THESPINALCORD Themajorityofanteriorramimergewithoneormoreadjacent anteriorrami,formingthemajorsomaHcnerveplexuses. Themostperipheralnervesarisingfromtheplexuscontainfibersfrom mulHplespinalnerves. ThespinalnerveslosetheiridenHtyastheysplitandmergeinthe plexus. THESOMATICANDVISCERALFIBERS THESPINALCORD Thetypesoffibersconveyedbyspinalnervesare: 1.SomaHcfibers a.Generalsensoryfibers b.SomaHcmotorfibers 2.Visceralfibers a.Visceralsensoryfibers b.Visceralmotorfibers THESPINALCORD Generalsensoryfibers(generalsomaHcafferent[GSA]fibers) transmitsensaHonsfromthebodytotheCNS. TheymaybeexterocepHvesensaHonsfromtheskin(pain, temperature,touch,andpressure)orpainandpropriocepHve sensaHonsfrommuscles,tendons,andjoints. SomaHcmotorfibers(generalsomaHcefferent[GSE]fibers)transmit impulsestoskeletal(voluntary)muscles. THESPINALCORD Visceralsensoryfibers(generalvisceralafferent[GVA]fibers)transmit painorsubconsciousvisceralreflexsensaHons(informaHon concerningdistension,bloodgas,andbloodpressurelevels)from holloworgansandbloodvesselstotheCNS. Visceralmotorfibers(generalvisceralefferent[GVE]fibers)transmit impulsestosmooth(involuntary)muscleandglandularHssues. Visceralmotorfibers(generalvisceralefferent[GVE]fibers)Two varieHesoffibers,presynapHcandpostsynapHc,worktogetherto conductimpulsesfromtheCNStosmoothmuscleorglands. THESPINALCORD Bothtypesofsensoryfibers:visceralsensoryandgeneral sensory,areprocessesofpseudounipolarneuronswithcell bodieslocatedinspinalsensoryganglia. ThemotorfibersofnervesareaxonsofmulHpolarneurons. ThecellbodiesofsomaHcmotorandpresynapHcvisceralmotor neuronsarelocatedinthegraymaRerofthespinalcord. SPINALMENINGES AND CEREBROSPINALFLUID(CSF) THESPINALCORD Thespinalduramater,arachnoidmater,andpiamatersurrounding thespinalcordconsHtutethespinalmeninges. Thespinalmeninges: • spinalduramater • arachnoidmater • piamater THESPINALCORD Thespinalduraisseparatedfromtheperiosteum-coveredboneand theligamentsthatformthewallsofthevertebralcanalbythe epiduralspace. Thisspaceisoccupiedbytheinternalvertebralvenousplexus embeddedinafaSymatrix(epiduralfat). Thespinalduraformsthespinalduralsac,alongtubularsheath withinthevertebralcanal. Thespinalduralsacisevaginatedbyeachpairofposteriorand anteriorroots. THESPINALCORD INNERVATIONOFDURAMATER Nervefibersaredistributedtothespinaldurabythe(recurrent) meningealnerves THESPINALCORD Thespinalarachnoidmaterisadelicate,avascularmembrane thatlinesthespinalduralsacanditsduralrootsheaths. ThespinalarachnoidmaterenclosestheCSF-filledsubarachnoid spacecontainingthespinalcord,spinalnerveroots,andspinal ganglia. ThespinalarachnoidisnotaRachedtothespinaldurabutisheld againstitsinnersurfacebythepressureoftheCSF. THESPINALCORD Inalumbarspinalpuncture,theneedletraversesthespinalduraand arachnoid. Bleedingintothislayercreatesapathologicalspaceatthedura- arachnoidjuncHoninwhichasubduralhematomaisformed. THESPINALCORD Thespinalarachnoidisseparatedfromthepiamateronthesurfaceof thespinalcordbythesubarachnoidspacecontainingCSF. Thearachnoidtrabeculae,spanthesubarachnoidspaceconnecHng thespinalarachnoidandpia. THESPINALCORD Thespinalpiamater,theinnermostmembrane,closelyfollows allthesurfacefeaturesofthespinalcord. Thespinalpiaalsodirectlycoverstherootsofthespinalnervesand thespinalbloodvessels. Thespinalcordissuspendedintheduralsacbythefilumterminale andtherightandle]denHculateligaments. THESPINALCORD SUBARACHNOIDSPACE Thesubarachnoidspaceislocatedbetweenthearachnoidandpia materandisfilledwithCSF. Thelumbarcistern-theenlargementofthesubarachnoidspacein theduralsac,caudaltotheconusmedullarisandcontainingCSFand thecaudaequina. THESPINALCORD ARTERIESOFSPINALCORDANDNERVEROOTS THESPINALCORD Thearteriessupplyingthespinalcordarebranchesofthe: • vertebral • ascendingcervical • deepcervical • intercostal • lumbar • lateralsacralarteries Threelongitudinalarteriessupplythespinalcord: • anteriorspinalartery • pairedposteriorspinalarteries. THESPINALCORD Thesearteriesrunlongitudinallyfromthemedullaofthebrainstemto theconusmedullarisofthespinalcord. Theanteriorspinalartery,formedbytheunionofbranchesofthe vertebralarteries,runsinferiorlyintheanteriormedianfissure. Theposteriorspinalarteryisabranchofeitherthevertebralarteryor theposteroinferiorcerebellarartery. THESPINALCORD Theanteriorandposteriorsegmentalmedullaryarteriesarederived fromspinalbranchesofthe: • ascendingcervical • deepcervical • vertebral • posteriorintercostal • lumbararteries. TheyenterthevertebralcanalthroughtheIVforamina. Theposteriorandanteriorrootsofthespinalnervesandtheir coveringsaresuppliedbyposteriorandanteriorradiculararteries. THESPINALCORD VEINSOFSPINALCORD THESPINALCORD Thereareusuallythreeanteriorandthreeposteriorspinalveins Theveinsofthespinalcordjointheinternalvertebral(epidural) venousplexusesintheepiduralspace. Theinternalvertebralvenousplexusespasssuperiorlythroughthe foramenmagnumtocommunicatewithduralsinusesandvertebral veinsinthecranium. Theinternalvertebralplexusesalsocommunicatewiththe externalvertebralvenousplexuses. CERVICALSPINALCORDINJURY CERVICALSPINALCORDINJURY A45-year-oldmanwasinvolvedinaseriouscaraccident. OnexaminaHonhehadasevereinjurytothecervical regionofhisvertebralcolumnwithdamagetothespinal cord. Infact,hisbreathingbecameerraHcandstopped. CERVICALSPINALCORDINJURY IfthecervicalspinalcordinjuryisabovethelevelofC5,breathingis likelytostop. CERVICALSPINALCORDINJURY Thephrenicnervetakesoriginfrom • C3, • C4, • andC5 andsuppliesthediaphragm. CERVICALSPINALCORDINJURY BreathingmaynotceaseimmediatelyifthelesionisjustbelowC5, butdoessoasthecordbecomesedematousand damageprogressessuperiorly. CERVICALSPINALCORDINJURY InaddiHon,somerespiratoryandvenHlatoryexchangemayoccurby usingneckmusclesplusthesternocleidomastoidandtrapezius muscles,whichareinnervatedbytheaccessorynerve[XI]. CERVICALSPINALCORDINJURY ThepaHentwasunabletosenseormovehis upperandlowerlimbs. CERVICALSPINALCORDINJURY ThepaHenthasparalysisoftheupperandlowerlimbsandis thereforequadriplegic. CERVICALSPINALCORDINJURY Ifbreathingisunaffected,thelesionisbelowthelevelofC5or atthelevelofC5. CERVICALSPINALCORDINJURY Thenervesupplytotheupperlimbsisviathebrachialplexus, whichbeginsattheC5level. CERVICALSPINALCORDINJURY ThesiteofthespinalcordinjuryisatorabovetheC5level. CERVICALSPINALCORDINJURY Itisimportanttorememberthatalthoughthecordhasbeen transectedinthecervicalregion,thecordbelowthislevelis intact. CERVICALSPINALCORDINJURY ReflexacHvitymaythereforeoccurbelowtheinjury, butcommunicaHonwiththebrainislost.
