VestibularVestibular FunctionFunction andand AnatomyAnatomy UTMBUTMB GrandGrand RoundsRounds AprilApril 14,14, 20042004 GordonGordon Shields,Shields, MDMD ArunArun Gadre,Gadre, MDMD SystemSystem ofof balancebalance MembranousMembranous andand bonybony labyrinthlabyrinth embeddedembedded inin petrouspetrous bonebone 55 distinctdistinct endend organsorgans –– 33 semicircularsemicircular canals:canals: superior,superior, lateral,lateral, posteriorposterior –– 22 otolithotolith organs:organs: utricleutricle andand sacculesaccule SemicircularSemicircular canalscanals sensesense angularangular accelerationacceleration OtolithicOtolithic organsorgans (utricle(utricle andand sacculesaccule)) sensesense linearlinear accelerationacceleration EmbryologyEmbryology 3rd3rd weekweek ofof embryonicembryonic developmentdevelopment OticOtic placodeplacode formedformed fromfrom neuroectodermneuroectoderm andand ectodermectoderm OtocystOtocyst oror oticotic vesiclevesicle 4th4th weekweek EmbryologyEmbryology EndolymphaticEndolymphatic ductduct formsforms UtricularUtricular chamberchamber becomesbecomes utricle/semicircularutricle/semicircular canalscanals SaccularSaccular chamberchamber becomesbecomes sacculesaccule/cochlea/cochlea SeparationSeparation ofof sacculesaccule andand cochleacochlea--ductusductus reuniensreuniens EmbryologyEmbryology WeekWeek 33 sensorysensory epitheliaepithelia developdevelop fromfrom ectodermectoderm 33 cristaecristae,, 22 maculaemaculae VestibulocochlearVestibulocochlear ganglionganglion startsstarts asas oneone thenthen spitsspits intointo superiorsuperior andand inferiorinferior divisionsdivisions – Superior division: Superior/lateral canals, utricle – Inferior division: saccule, posterior canal (via singular nerve) SemicircularSemicircular canalscanals areare orthogonalorthogonal toto eacheach otherother LateralLateral canalcanal inclinedinclined toto 3030 degreesdegrees Superior/Superior/postereorpostereor canalscanals 4545 degreesdegrees offoff ofof sagittalsagittal planeplane UtricleUtricle isis inin horizontalhorizontal planeplane SacculeSaccule isis inin verticalvertical planeplane AnatomyAnatomy ThereThere areare fivefive openingsopenings intointo areaarea ofof utricleutricle SacculeSaccule inin sphericalspherical recessrecess UtricleUtricle inin ellipticalelliptical recessrecess 45%45% fromfrom AICAAICA 24%24% superiorsuperior cerebellarcerebellar arteryartery 16%16% basilarbasilar TwoTwo divisions:divisions: anterioranterior vestibularvestibular andand commoncommon cochlearcochlear arteryartery SuperiorSuperior vestibularvestibular nerve:nerve: superiorsuperior canal,canal, laterallateral canal,canal, utricleutricle InferiorInferior vestibularvestibular nerve:nerve: posteriorposterior canalcanal andand sacculesaccule MembranousMembranous labyrinthlabyrinth isis surroundedsurrounded byby perilymphperilymph EndolymphEndolymph fillsfills thethe vestibularvestibular endend organsorgans alongalong withwith thethe cochleacochlea PerilymphPerilymph –– SimilarSimilar toto extracellularextracellular fluidfluid –– K+=10mEQ,K+=10mEQ, Na+=140mEq/LNa+=140mEq/L –– UnclearUnclear whetherwhether thisthis isis ultrafiltrateultrafiltrate ofof CSFCSF oror bloodblood –– DrainsDrains viavia venulesvenules andand middlemiddle earear mucosamucosa EndolymphEndolymph –– SimilarSimilar toto intracellularintracellular fluidfluid –– K+=144mEq/L,K+=144mEq/L, Na+=5mEq/LNa+=5mEq/L –– ProducedProduced byby marginalmarginal cellscells inin striastria vascularisvascularis fromfrom perilymphperilymph atat thethe cochleacochlea andand fromfrom darkdark cellscells inin thethe cristaecristae andand maculaemaculae –– AbsorbedAbsorbed inin endolymphaticendolymphatic sacsac whichwhich connectedconnected byby endolymphaticendolymphatic,, utricularutricular andand saccularsaccular ductsducts SensorySensory structuresstructures AmpullaAmpulla ofof thethe semicircularsemicircular canalscanals DilatedDilated endend ofof canalcanal ContainsContains sensorysensory neuroepitheliumneuroepithelium,, cupulacupula,, supportingsupporting cellscells CupulaCupula isis gelatinousgelatinous massmass extendingextending acrossacross atat rightright angleangle ExtendsExtends completelycompletely across,across, notnot responsiveresponsive toto gravitygravity CristaCrista ampullarisampullaris isis mademade upup ofof sensorysensory hairhair cellscells andand supportingsupporting cellscells Sensory cells are either Type I or Type II Type I cells are flask shaped and have chalice shaped calyx ending One chalice may synapse with 2-4 Type I cells Type II cells – cylinder shaped, multiple efferent and afferent boutons Hair cells have 50-100 stereocilia and a single kinocilium. stereocilia are not true cilia, they are graded in height with tallest nearest the kinocilium. KinociliumKinocilium isis locatedlocated onon oneone endend ofof cellcell givinggiving eacheach cellcell aa polaritypolarity HasHas 9+29+2 arrangementarrangement ofof microtubulemicrotubule doubletsdoublets LacksLacks innerinner dyneindynein arms,arms, andand centralcentral portionportion ofof microtubulesmicrotubules notnot presentpresent nearnear endsends –– maymay meanmean theythey areare immobileimmobile oror weaklyweakly mobilemobile EachEach afferentafferent neuronneuron hashas aa baselinebaseline firingfiring raterate DeflectionDeflection ofof stereociliastereocilia towardtoward kinociliumkinocilium resultsresults inin anan increaseincrease inin thethe firingfiring raterate ofof thethe afferentafferent neuronneuron DeflectionDeflection awayaway causescauses aa decreasedecrease inin thethe firingfiring raterate kinociliakinocilia areare locatedlocated closestclosest toto utricleutricle inin laterallateral canalscanals andand areare onon canalicularcanalicular sideside inin otherother canalscanals AmpullopetalAmpullopetal flowflow (toward(toward thethe ampullaampulla)) excitatoryexcitatory inin laterallateral canals,canals, inhibitoryinhibitory inin superior/posteriorsuperior/posterior canalscanals AmpullofugalAmpullofugal flowflow (away(away fromfrom thethe ampullaampulla)) hashas oppositeopposite effecteffect Semicircular canals are paired – Horizontal canals – Right superior/left posterior – Left superior/right posterior – Allow redundant reception of movement – Explains compensation after unilateral vestibular loss OtolithicOtolithic organsorgans UtricleUtricle andand sacculesaccule sensesense linearlinear accelerationacceleration CiliaCilia fromfrom hairhair cellscells areare embeddedembedded inin gelatinousgelatinous layerlayer OtolithsOtoliths oror otoconiaotoconia areare onon upperupper surfacesurface CalciumCalcium carbonatecarbonate oror calcitecalcite 0.50.5--30um30um SpecificSpecific gravitygravity ofof otolithicotolithic membranemembrane isis 2.712.71--2.942.94 CentralCentral regionregion ofof otolithicotolithic membranemembrane isis calledcalled thethe striolastriola SacculeSaccule hashas hairhair cellscells orientedoriented awayaway fromfrom thethe striolastriola UtricleUtricle hashas hairhair cellscells orientedoriented towardstowards thethe striolastriola StriolaStriola isis curvedcurved soso otolithicotolithic organsorgans areare sensitivesensitive toto linearlinear motionmotion inin multiplemultiple trajectoriestrajectories CentralCentral connectionsconnections Scarpa’sScarpa’s ganglionganglion isis inin thethe internalinternal auditoryauditory canalcanal ContainsContains bipolarbipolar ganglionganglion cellscells ofof firstfirst orderorder neuronsneurons SuperiorSuperior andand inferiorinferior divisionsdivisions formform commoncommon bundlebundle whichwhich entersenters brainstembrainstem NoNo primaryprimary vestibularvestibular afferentsafferents crosscross thethe midlinemidline AfferentAfferent fibersfibers terminateterminate inin thethe vestibularvestibular nucleinuclei inin floorfloor ofof fourthfourth ventricleventricle –– SuperiorSuperior vestibularvestibular nucleusnucleus –– LateralLateral vestibularvestibular nucleusnucleus –– MedialMedial vestibularvestibular nucleusnucleus –– DescendingDescending vestibularvestibular nucleusnucleus VestibularVestibular nucleinuclei projectproject toto –– CerebellumCerebellum –– ExtraocularExtraocular nucleinuclei –– SpinalSpinal cordcord –– ContralateralContralateral vestibularvestibular nucleinuclei SensesSenses andand controlscontrols motionmotion InformationInformation isis combinedcombined withwith thatthat fromfrom visualvisual systemsystem andand proprioceptiveproprioceptive systemsystem MaintainsMaintains balancebalance andand compensatescompensates forfor effectseffects ofof headhead motionmotion Vestibulo-ocular reflex – Membranous labyrinth moves with head motion – Endolymph does not causing relative motion – Cupula on right canal deflected towards utricle causing increase in firing rate, left deflects away causing a decrease in firing rate. – Reflex causes movement of eyes to the left with saccades to right – Stabilizes visual image IfIf accelerationacceleration stops,stops, andand spinspin toto rightright isis atat constantconstant velocity,velocity, sensationsensation ofof motionmotion stopsstops afterafter 1414--2020 secondsseconds asas doesdoes nystagmusnystagmus CupulaCupula onlyonly takestakes 88--1010 secondsseconds toto returnreturn toto equilibriumequilibrium positionposition VestibularVestibular integratorintegrator isis thethe termterm forfor thethe prolongationprolongation andand isis mediatedmediated byby thethe vestibularvestibular