vestibular slides 2004 0414

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Vestibular Function andVestibular Function andAnatomyAnatomy

UTMB Grand RoundsUTMB Grand Rounds

April 14, 2004April 14, 2004Gordon Shields, MDGordon Shields, MD

Arun Gadre, MDArun Gadre, MD


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System of balanceSystem of balance

Membranous and bony labyrinthMembranous and bony labyrinthembedded inembedded in petrouspetrous bonebone

5 distinct end organs5 distinct end organs 3 semicircular canals: superior, lateral,3 semicircular canals: superior, lateral,

posteriorposterior

22 otolithotolith organs: utricle andorgans: utricle and sacculesaccule


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Semicircular canals sense angularSemicircular canals sense angular

accelerationacceleration OtolithicOtolithic organs (utricle andorgans (utricle and sacculesaccule))

sense linear accelerationsense linear acceleration


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EmbryologyEmbryology

3rd week of3rd week of

embryonicembryonicdevelopmentdevelopment

OticOtic placodeplacode formedformed

fromfrom neuroectodermneuroectodermand ectodermand ectoderm

OtocystOtocyst

oror

oticotic

vesiclevesicle

4th week4th week


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EndolymphaticEndolymphatic duct formsduct forms

UtricularUtricular chamber becomeschamber becomesutricle/semicircular canalsutricle/semicircular canals

SaccularSaccular chamber becomeschamber becomessacculesaccule/cochlea/cochlea

Separation ofSeparation of sacculesaccule and cochleaand cochlea--ductusductusreuniensreuniens


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Week 3 sensory epithelia develop from ectodermWeek 3 sensory epithelia develop from ectoderm

33 cristaecristae, 2 maculae, 2 maculae VestibulocochlearVestibulocochlear ganglion starts as one thenganglion starts as one then

spits into superior and inferior divisionsspits into superior and inferior divisions

Superior division: Superior/lateral canals, utricleSuperior division: Superior/lateral canals, utricle

Inferior division:Inferior division: sacculesaccule, posterior canal (via singular, posterior canal (via singular

nerve)nerve)


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Semicircular canalsSemicircular canals

are orthogonal toare orthogonal toeach othereach other

Lateral canal inclinedLateral canal inclined

to 30 degreesto 30 degrees Superior/Superior/postereorpostereor

canals 45 degrees offcanals 45 degrees off

ofof sagittalsagittal planeplane


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AnatomyAnatomy


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There are fiveThere are five

openings into area ofopenings into area ofutricleutricle

SacculeSaccule in sphericalin spherical

recessrecess Utricle in ellipticalUtricle in elliptical

recessrecess


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45% from AICA45% from AICA

24% superior24% superiorcerebellarcerebellar arteryartery

16% basilar16% basilar

Two divisions:Two divisions:

anterior vestibularanterior vestibular

and common cochlearand common cochleararteryartery


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Superior vestibularSuperior vestibular

nerve: superior canal,nerve: superior canal,lateral canal, utriclelateral canal, utricle

Inferior vestibularInferior vestibular

nerve: posterior canalnerve: posterior canalandand sacculesaccule


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Membranous labyrinth is surrounded byMembranous labyrinth is surrounded by

perilymphperilymph EndolymphEndolymph fills the vestibular end organsfills the vestibular end organs

along with the cochleaalong with the cochlea


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PerilymphPerilymph

Similar toSimilar to extracellularextracellular fluidfluid K+=10mEQ, Na+=140mEq/LK+=10mEQ, Na+=140mEq/L

Unclear whether this isUnclear whether this is ultrafiltrateultrafiltrate of CSF orof CSF orbloodblood

Drains viaDrains via venulesvenules and middle ear mucosaand middle ear mucosa


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EndolymphEndolymph

Similar to intracellular fluidSimilar to intracellular fluid K+=144mEq/L, Na+=5mEq/LK+=144mEq/L, Na+=5mEq/L

Produced by marginal cells inProduced by marginal cells in striastria vascularisvascularisfromfrom perilymphperilymph at the cochlea and from darkat the cochlea and from dark

cells in thecells in the cristaecristae and maculaeand maculae

Absorbed inAbsorbed in endolymphaticendolymphatic sac whichsac whichconnected byconnected by endolymphaticendolymphatic,, utricularutricular andand

saccularsaccular ductsducts


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CupulaCupula is gelatinousis gelatinousmass extendingmass extendingacross at right angleacross at right angle

Extends completelyExtends completely

across, not responsiveacross, not responsiveto gravityto gravity

CristaCrista ampullarisampullaris isis

made up of sensorymade up of sensoryhair cells andhair cells andsupporting cellssupporting cells


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Sensory cells are eitherSensory cells are either

Type I or Type IIType I or Type II

Type I cells are flaskType I cells are flask

shaped and have chaliceshaped and have chalice

shaped calyx endingshaped calyx ending

One chalice may synapseOne chalice may synapse

with 2with 2--4 Type I cells4 Type I cells

Type II cellsType II cells cylindercylinder

shaped, multiple efferentshaped, multiple efferentand afferentand afferent boutonsboutons


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Hair cells have 50-100 stereocilia and a singlekinocilium.


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stereocilia are not true cilia, they are graded in height with tallestnearest the kinocilium.


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KinociliumKinocilium is located on one end of cellis located on one end of cell

giving each cell a polaritygiving each cell a polarity Has 9+2 arrangement of microtubuleHas 9+2 arrangement of microtubule

doubletsdoublets Lacks innerLacks inner dyneindynein arms, and centralarms, and central

portion of microtubules not present nearportion of microtubules not present near

endsends may mean they are immobile ormay mean they are immobile orweakly mobileweakly mobile


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kinociliakinocilia are located closest to utricle inare located closest to utricle in

lateral canals and are onlateral canals and are on canalicularcanalicular sidesidein other canalsin other canals

AmpullopetalAmpullopetal flow (toward theflow (toward the ampullaampulla))excitatory in lateral canals, inhibitory inexcitatory in lateral canals, inhibitory in

superior/posterior canalssuperior/posterior canals

AmpullofugalAmpullofugal flow (away from theflow (away from theampullaampulla) has opposite effect) has opposite effect


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Semicircular canals areSemicircular canals are

pairedpaired

Horizontal canalsHorizontal canals

Right superior/left posteriorRight superior/left posterior

Left superior/right posteriorLeft superior/right posterior

Allow redundant receptionAllow redundant receptionof movementof movement

Explains compensationExplains compensation

after unilateral vestibularafter unilateral vestibular

lossloss


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OtolithicOtolithic organsorgans

Utricle andUtricle and sacculesaccule sense linearsense linear

accelerationacceleration Cilia from hair cells are embedded inCilia from hair cells are embedded in

gelatinous layergelatinous layer OtolithsOtoliths oror otoconiaotoconia are on upper surfaceare on upper surface


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Calcium carbonate orCalcium carbonate or

calcitecalcite 0.50.5--30um30um

Specific gravity ofSpecific gravity of

otolithicotolithic membrane ismembrane is2.712.71--2.942.94

Central region ofCentral region of

otolithicotolithic membrane ismembrane is

called thecalled the striolastriola


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SacculeSaccule has hair cellshas hair cellsorientedoriented awayaway fromfromthethe striolastriola

Utricle has hair cellsUtricle has hair cellsorientedoriented towardstowards thethestriolastriola

StriolaStriola is curved sois curved so

otolithicotolithic organs areorgans aresensitive to linearsensitive to linearmotion in multiplemotion in multipletrajectoriestrajectories


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Central connectionsCentral connections

ScarpasScarpas ganglion is in the internalganglion is in the internal

auditory canalauditory canal Contains bipolar ganglion cells of firstContains bipolar ganglion cells of first

order neuronsorder neurons

Superior and inferior divisions formSuperior and inferior divisions form

common bundle which enters brainstemcommon bundle which enters brainstem

No primary vestibular afferents cross theNo primary vestibular afferents cross the

midlinemidline


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Afferent fibers terminate in the vestibularAfferent fibers terminate in the vestibular

nuclei in floor of fourth ventriclenuclei in floor of fourth ventricle Superior vestibular nucleusSuperior vestibular nucleus

Lateral vestibular nucleusLateral vestibular nucleus

Medial vestibular nucleusMedial vestibular nucleus

Descending vestibular nucleusDescending vestibular nucleus


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Vestibular nuclei project toVestibular nuclei project to

CerebellumCerebellum ExtraocularExtraocular nucleinuclei

Spinal cordSpinal cord

Contralateral vestibular nucleiContralateral vestibular nuclei


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Senses and controlsSenses and controlsmotionmotion

Information isInformation iscombined with thatcombined with thatfrom visual systemfrom visual systemandand proprioceptiveproprioceptivesystemsystem

Maintains balance andMaintains balance andcompensates forcompensates foreffects of headeffects of headmotionmotion


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VestibuloVestibulo--ocular reflexocular reflex Membranous labyrinthMembranous labyrinth

moves with head motionmoves with head motion

EndolymphEndolymph does notdoes notcausing relative motioncausing relative motion

CupulaCupula on right canalon right canaldeflected towards utricledeflected towards utricle

causing increase in firingcausing increase in firingrate, left deflects awayrate, left deflects awaycausing a decrease in firingcausing a decrease in firingrate.rate.

Reflex causes movement ofReflex causes movement ofeyes to the left witheyes to the left withsaccades to rightsaccades to right

Stabilizes visual imageStabilizes visual image


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If acceleration stops, and spin to right isIf acceleration stops, and spin to right is

at constant velocity, sensation of motionat constant velocity, sensation of motionstops after 14stops after 14--20 seconds as does20 seconds as doesnystagmusnystagmus

CupulaCupula only takes 8only takes 8--10 seconds to return10 seconds to returnto equilibrium positionto equilibrium position

Vestibular integrator is the term for theVestibular integrator is the term for theprolongation and is mediated by theprolongation and is mediated by thevestibular nuclei and cerebellumvestibular nuclei and cerebellum

b l l fl


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VestibulospinalVestibulospinal ReflexReflex

Senses head movement and head relativeSenses head movement and head relative

to gravityto gravity Projects to antigravity muscles via 3 majorProjects to antigravity muscles via 3 major

pathways:pathways:

LateralLateral vestibulospinalvestibulospinal tracttract

MedialMedial vestibulospinalvestibulospinal tracttract

ReticulospinalReticulospinal tracttract

dH d ll i kk?


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How doHow do caloricscalorics work?work?

Patient is lying down withPatient is lying down with

horizontal canals orientedhorizontal canals oriented

vertically (vertically (ampullaampulla up)up) Cold water irrigation causesCold water irrigation causes

endolymphendolymph in lateral portion toin lateral portion to

become dense and fall causingbecome dense and fall causing

deflection ofdeflection of cupulacupula away fromaway fromutricle with a decrease in theutricle with a decrease in the

firing ratefiring rate

This causesThis causes nystagmusnystagmus withwith

fast phase (beat) away fromfast phase (beat) away fromthe stimulusthe stimulus


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With warm water irrigationWith warm water irrigation

column ofcolumn of endolymphendolymph becomesbecomes

less dense, rises and causesless dense, rises and causesdeflection ofdeflection of cupulacupula toward thetoward the

utricleutricle

Results in increase firing rateResults in increase firing rate

andand nystagmusnystagmus which beatswhich beatstowards the stimulationtowards the stimulation

COWS (cold opposite, warmCOWS (cold opposite, warm

same)same)


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SS


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SourcesSourcesShepard NT, Solomon D. Functional Operation of the Balance System in

Daily Activities. Otolaryngologic Clinics of North America2000;33(3):455-468.

Minor LB. Physiological principles of vestibular function on earth and inspace. Otolaryngology-Head and Neck Surgery 1998;118(3 part 2):S5-S15.

Abdel Razek OA. Anatomy of the Vestibular System. www.emedicine.comHoffman R, Strunk C. Vestibular Anatomy and Physiology. Department of

Otolaryngology Grand Rounds University of Texas Medical BranchDecember 9, 1992.

Baloh RW. Dizziness, Hearing Loss, and Tinnitus. Philadephia, F.A. DavisCompany, 1998.

Jahn AF, Santos-Sacchi J. Physiology of the Ear. Second edition. San Diego,Singular, 2001.

Friedman I, Ballantyne J. Ultrastructural Atlas of the Inner Ear. London,Butterworth & Co., 1984.

Janfaza P, Nadol JB. Temporal Bone and Ear. In: Janfaza P ed. SurgicalAnatomy of the Head and Neck. Philadelphia, Lippincott Williams &Wilkins, 2001:419-479.

Wall C, Vrabec JT. Vestibular Function and Anatomy. In: Head & NeckSurgery-Otolaryngolog. Philadelphia, Lippincott Williams & Wilkins,2001:1641-1650.
http://www.emedicine.com/http://www.emedicine.com/

vestibular slides 2004 0414

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