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Vestibular Function Vestibular Function and Anatomyand Anatomy
UTMB Grand Rounds UTMB Grand Rounds
April 14, 2004April 14, 2004
Gordon Shields, MDGordon Shields, MD
Arun Gadre, MDArun Gadre, MD
System of balanceSystem of balance Membranous and bony labyrinth Membranous and bony labyrinth
embedded in petrous boneembedded in petrous bone 5 distinct end organs5 distinct end organs
– 3 semicircular canals: superior, lateral, 3 semicircular canals: superior, lateral, posteriorposterior
– 2 otolith organs: utricle and saccule2 otolith organs: utricle and saccule
Semicircular canals sense angular Semicircular canals sense angular accelerationacceleration
Otolithic organs (utricle and saccule) Otolithic organs (utricle and saccule) sense linear accelerationsense linear acceleration
EmbryologyEmbryology
3rd week of 3rd week of embryonic embryonic developmentdevelopment
Otic placode Otic placode formed from formed from neuroectoderm neuroectoderm and ectodermand ectoderm
Otocyst or otic Otocyst or otic vesicle 4th weekvesicle 4th week
EmbryologyEmbryology
Endolymphatic duct forms Endolymphatic duct forms Utricular chamber becomes Utricular chamber becomes
utricle/semicircular canalsutricle/semicircular canals Saccular chamber becomes Saccular chamber becomes
saccule/cochleasaccule/cochlea Separation of saccule and cochlea-Separation of saccule and cochlea-
ductus reuniensductus reuniens
EmbryologyEmbryology
Week 3 sensory epithelia develop from Week 3 sensory epithelia develop from ectodermectoderm
3 cristae, 2 maculae 3 cristae, 2 maculae Vestibulocochlear ganglion starts as one Vestibulocochlear ganglion starts as one
then spits into superior and inferior then spits into superior and inferior divisionsdivisions– Superior division: Superior/lateral canals, Superior division: Superior/lateral canals,
utricleutricle– Inferior division: saccule, posterior canal (via Inferior division: saccule, posterior canal (via
singular nerve)singular nerve)
Semicircular canals Semicircular canals are orthogonal to are orthogonal to each othereach other
Lateral canal Lateral canal inclined to 30 inclined to 30 degreesdegrees
Superior/postereor Superior/postereor canals 45 degrees canals 45 degrees off of sagittal planeoff of sagittal plane
Utricle is in Utricle is in horizontal planehorizontal plane
Saccule is in Saccule is in vertical planevertical plane
AnatomyAnatomy
There are five There are five openings into area openings into area of utricleof utricle
Saccule in Saccule in spherical recessspherical recess
Utricle in elliptical Utricle in elliptical recessrecess
45% from AICA45% from AICA 24% superior 24% superior
cerebellar arterycerebellar artery 16% basilar16% basilar Two divisions: Two divisions:
anterior vestibular anterior vestibular and common and common cochlear arterycochlear artery
Superior vestibular Superior vestibular nerve: superior nerve: superior canal, lateral canal, canal, lateral canal, utricleutricle
Inferior vestibular Inferior vestibular nerve: posterior nerve: posterior canal and sacculecanal and saccule
Membranous labyrinth is surrounded Membranous labyrinth is surrounded by perilymphby perilymph
Endolymph fills the vestibular end Endolymph fills the vestibular end organs along with the cochleaorgans along with the cochlea
PerilymphPerilymph– Similar to extracellular fluidSimilar to extracellular fluid– K+=10mEQ, Na+=140mEq/LK+=10mEQ, Na+=140mEq/L– Unclear whether this is ultrafiltrate of Unclear whether this is ultrafiltrate of
CSF or bloodCSF or blood– Drains via venules and middle ear Drains via venules and middle ear
mucosamucosa
EndolymphEndolymph– Similar to intracellular fluidSimilar to intracellular fluid– K+=144mEq/L, Na+=5mEq/LK+=144mEq/L, Na+=5mEq/L– Produced by marginal cells in stria Produced by marginal cells in stria
vascularis from perilymph at the cochlea vascularis from perilymph at the cochlea and from dark cells in the cristae and and from dark cells in the cristae and maculaemaculae
– Absorbed in endolymphatic sac which Absorbed in endolymphatic sac which connected by endolymphatic, utricular connected by endolymphatic, utricular and saccular ductsand saccular ducts
Sensory structuresSensory structures
Ampulla of the semicircular canalsAmpulla of the semicircular canals Dilated end of canalDilated end of canal Contains sensory neuroepithelium, Contains sensory neuroepithelium,
cupula, supporting cellscupula, supporting cells
Cupula is gelatinous Cupula is gelatinous mass extending mass extending across at right angleacross at right angle
Extends completely Extends completely across, not across, not responsive to gravityresponsive to gravity
Crista ampullaris is Crista ampullaris is made up of sensory made up of sensory hair cells and hair cells and supporting cellssupporting cells
Sensory cells are either Sensory cells are either Type I or Type IIType I or Type II
Type I cells are flask Type I cells are flask shaped and have chalice shaped and have chalice shaped calyx ending shaped calyx ending
One chalice may One chalice may synapse with 2-4 Type I synapse with 2-4 Type I cellscells
Type II cells – cylinder Type II cells – cylinder shaped, multiple shaped, multiple efferent and afferent efferent and afferent boutonsboutons
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.
Kinocilium is located on one end of Kinocilium is located on one end of cell giving each cell a polaritycell giving each cell a polarity
Has 9+2 arrangement of microtubule Has 9+2 arrangement of microtubule doubletsdoublets
Lacks inner dynein arms, and central Lacks inner dynein arms, and central portion of microtubules not present portion of microtubules not present near ends – may mean they are near ends – may mean they are immobile or weakly mobileimmobile or weakly mobile
Each afferent neuron has a baseline Each afferent neuron has a baseline firing ratefiring rate
Deflection of stereocilia toward Deflection of stereocilia toward kinocilium results in an increase in kinocilium results in an increase in the firing rate of the afferent neuronthe firing rate of the afferent neuron
Deflection away causes a decrease in Deflection away causes a decrease in the firing ratethe firing rate
kinocilia are located closest to utricle kinocilia are located closest to utricle in lateral canals and are on in lateral canals and are on canalicular side in other canalscanalicular side in other canals
Ampullopetal flow (toward the Ampullopetal flow (toward the ampulla) excitatory in lateral canals, ampulla) excitatory in lateral canals, inhibitory in superior/posterior canals inhibitory in superior/posterior canals
Ampullofugal flow (away from the Ampullofugal flow (away from the ampulla) has opposite effectampulla) has opposite effect
Semicircular canals Semicircular canals are pairedare paired– Horizontal canalsHorizontal canals– Right superior/left Right superior/left
posteriorposterior– Left superior/right Left superior/right
posteriorposterior– Allow redundant Allow redundant
reception of movementreception of movement– Explains compensation Explains compensation
after unilateral after unilateral vestibular lossvestibular loss
Otolithic organsOtolithic organs
Utricle and saccule sense linear Utricle and saccule sense linear accelerationacceleration
Cilia from hair cells are embedded in Cilia from hair cells are embedded in gelatinous layer gelatinous layer
Otoliths or otoconia are on upper Otoliths or otoconia are on upper surfacesurface
Calcium carbonate Calcium carbonate or calciteor calcite
0.5-30um0.5-30um Specific gravity of Specific gravity of
otolithic membrane otolithic membrane is 2.71-2.94is 2.71-2.94
Central region of Central region of otolithic membrane otolithic membrane is called the striolais called the striola
Saccule has hair Saccule has hair cells oriented cells oriented awayaway from the striolafrom the striola
Utricle has hair Utricle has hair cells oriented cells oriented towardstowards the striola the striola
Striola is curved so Striola is curved so otolithic organs are otolithic organs are sensitive to linear sensitive to linear motion in multiple motion in multiple trajectoriestrajectories
Central connectionsCentral connections
Scarpa’s ganglion is in the internal Scarpa’s ganglion is in the internal auditory canalauditory canal
Contains bipolar ganglion cells of first Contains bipolar ganglion cells of first order neuronsorder neurons
Superior and inferior divisions form Superior and inferior divisions form common bundle which enters common bundle which enters brainstembrainstem
No primary vestibular afferents cross No primary vestibular afferents cross the midlinethe midline
Afferent fibers terminate in the Afferent fibers terminate in the vestibular nuclei in floor of fourth vestibular nuclei in floor of fourth ventricleventricle– Superior vestibular nucleusSuperior vestibular nucleus– Lateral vestibular nucleusLateral vestibular nucleus– Medial vestibular nucleusMedial vestibular nucleus– Descending vestibular nucleusDescending vestibular nucleus
Vestibular nuclei project toVestibular nuclei project to– CerebellumCerebellum– Extraocular nucleiExtraocular nuclei– Spinal cordSpinal cord– Contralateral vestibular nucleiContralateral vestibular nuclei
Senses and Senses and controls motioncontrols motion
Information is Information is combined with that combined with that from visual system from visual system and proprioceptive and proprioceptive systemsystem
Maintains balance Maintains balance and compensates and compensates for effects of head for effects of head motionmotion
Vestibulo-ocular reflexVestibulo-ocular reflex– Membranous labyrinth Membranous labyrinth
moves with head moves with head motionmotion
– Endolymph does not Endolymph does not causing relative motioncausing relative motion
– Cupula on right canal Cupula on right canal deflected towards deflected towards utricle causing increase utricle causing increase in firing rate, left in firing rate, left deflects away causing a deflects away causing a decrease in firing rate.decrease in firing rate.
– Reflex causes Reflex causes movement of eyes to movement of eyes to the left with saccades the left with saccades to rightto right
– Stabilizes visual imageStabilizes visual image
If acceleration stops, and spin to If acceleration stops, and spin to right is at constant velocity, right is at constant velocity, sensation of motion stops after 14-20 sensation of motion stops after 14-20 seconds as does nystagmusseconds as does nystagmus
Cupula only takes 8-10 seconds to Cupula only takes 8-10 seconds to return to equilibrium positionreturn to equilibrium position
Vestibular integrator is the term for Vestibular integrator is the term for the prolongation and is mediated by the prolongation and is mediated by the vestibular nuclei and cerebellumthe vestibular nuclei and cerebellum
Vestibulospinal ReflexVestibulospinal Reflex
Senses head movement and head Senses head movement and head relative to gravityrelative to gravity
Projects to antigravity muscles via 3 Projects to antigravity muscles via 3 major pathways:major pathways:– Lateral vestibulospinal tractLateral vestibulospinal tract– Medial vestibulospinal tractMedial vestibulospinal tract– Reticulospinal tractReticulospinal tract
How do calorics work?How do calorics work? Patient is lying down with Patient is lying down with
horizontal canals oriented horizontal canals oriented vertically (ampulla up)vertically (ampulla up)
Cold water irrigation Cold water irrigation causes endolymph in causes endolymph in lateral portion to become lateral portion to become dense and fall causing dense and fall causing deflection of cupula away deflection of cupula away from utricle with a from utricle with a decrease in the firing ratedecrease in the firing rate
This causes nystagmus This causes nystagmus with fast phase (beat) with fast phase (beat) away from the stimulusaway from the stimulus
With warm water irrigation With warm water irrigation column of endolymph column of endolymph becomes less dense, rises becomes less dense, rises and causes deflection of and causes deflection of cupula toward the utriclecupula toward the utricle
Results in increase firing Results in increase firing rate and nystagmus which rate and nystagmus which beats towards the beats towards the stimulationstimulation
COWS (cold opposite, COWS (cold opposite, warm same)warm same)
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Hoffman R, Strunk C. Vestibular Anatomy and Physiology. Department of Otolaryngology Grand Rounds University of Texas Medical Branch December 9, 1992.
Baloh RW. Dizziness, Hearing Loss, and Tinnitus. Philadephia, F.A. Davis Company, 1998.
Jahn AF, Santos-Sacchi J. Physiology of the Ear. Second edition. San Diego, Singular, 2001.
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Janfaza P, Nadol JB. Temporal Bone and Ear. In: Janfaza P ed. Surgical Anatomy of the Head and Neck. Philadelphia, Lippincott Williams & Wilkins, 2001:419-479.
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