anatomy & embryology of vestibular system
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ANATOMY & EMBRYOLOGY OF VESTIBULAR SYSTEM
S Pandey
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VESTIBULAR SYSTEMprovides orientation in
3D spaceModification of muscle
tone & BalanceEssential for
coordinates of motor response, eye movement & posture
Sense of Balance poorly represented in centres of consciousness
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EMBRYOLOGY
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Vestibular systemPeripheral part located in
labyrinth, inner earVestibule & semicircular
canals dilations & carvings within petrous temporal (perilymph)
Memb labyrinth similar in shape but smaller (endolymph)
Stria vascularis in cochlear duct & secretory cells in transitional epithelium produce endolymph
Membranous labyrinth related to vestibular fxn consist of 3 semicircular ducts, Utricle and Saccule
Within these structures there are neuroepithelial cells = peripheral receptors of vestibular system
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The Semicircular Canals
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UTRICLE & SACCULE
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MaculaEach macula is a small area of sensory epithelium. The
ciliary bundles of the sensory cells project into the overlying statoconial membrane. The statoconial membrane is comprised of 3 layers, as follows:
The otoconial first layer The second layer is a gelatinous area of mucopolysaccharide
gel.The third layer consists of subcopula meshwork.The otoconia appear to be produced by the supporting cells
of the sensory epithelium and to be resorbed by the dark cell region.
On a morphologic basis, each macula can be divided into 2 areas by a narrow curved zone that extends through its middle. This zone has been termed the striola.
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Crista ampullarisConsists of a crest of
sensory epithelium supported on a mound of connective tissue
Bulbous wedge shaped, gelatinous mass called cupula surmounts the crista
Cilia of sensory cells project into cupula
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Vestibular hair cellsType 1 & 2Sensory cellsStereociliaKinociliumSupporting cells
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BLOOD SUPPLY
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INNERVATION Efferent innervation from the e group nucleus of the
brainstem. (200 cell bodies located lateral to abducens nucleus)
Fibers project ipsilaterally, contralaterally & bilaterallyTravel in ventral part of vestibular nerveParasympathetic innervation from intermediate nerve
fibers that become part of vestibular nerve near the vestibular ganglion after passing through geniculate ganglion of CNVII
Post Ganglionic fibers from superior cervical ganglionNon vascular sympathetic fibers travel along myelinated
afferent fibers. But do not innervate sensory epithelium of vestibular organs
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Vestibular nerveBranches into
superior division that innervates the ant & horizontal cristae ampullares and utricular macula
Inferior division that innervates post crista ampullaris & saccular macula
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OORT’s ANASTOMOSISThe vestibulocochlear anastomosis was first
described in 1918 by von Oort. It is situated deeply at the bottom of the internal acoustic meatus, and spreads from the saccular nerve before its terminal ramifications, to the cochlear nerve before its penetration into the cochlea. Nerve fibers of the cochlear efferent system are thought to pass through it.
VOIT’s nerve (branch of superior vestibular nerve running to the saccular macula. Also known as superiour saccular nerve
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VESTIBULAR NUCLEAR COMPLEX
4 Nuclei lie on lateral recess of rhomboid fossaLateral nucleus contains largest cells, inferior
nucleus contains smallest cells.Form two distinct cell columnsMedial vestibular nucleus is largest forms
medial cell columnSuperior, lateral & inferior vestibular nuclei
form lateral cell columnMost of nublei and interconnected through
commisural system
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Vestibular nuclei complex contdElectrical stim of utricular macula evokes
excitation in ipsilateral secondary vestibular neurons & inhibition in >50% of contralateral secondary vestibular neurons
Nucleus prepositus hypoglossiParasolitary nucleusNucleus XNucleus Z
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VESTIBULAR GANGLIA2 Ganglia, one on each sideCell bodies of afferents innervating
peripheral vestibular apparatus Each ganglion contains abt 20000 cellsDivided into superior & inferior part united
by isthmusPeripheral processes from sup ganglion
innervate ampullary crests of sup & lateral semicircular ducts & macula of utricle
Inf ganglion innervate macula of saccule
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Vestibular ganglia contd
•Central processes from vestibular ganglion form the vestibular nerve•Together with cochlear nerve, vestibular nerve courses in the internal auditory meatus as vestibulocochlear nerve•Passes through cerebellopontine angle and enter the pons to terminate in vestibular nuclear complex•Few fibers pass directly to flocculo nodular lobe of cerebellum•(primary vestibular fibers)
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Secondary vestibular fibersFrom medial and inferior vestibular nuclei
destined for flucculo nodular nobe and uvulaForm all vestibular nuclei travelling within
medial longitudinal fasciculus to reach cranial nerve motor nerve nuclei (innervating extraocular muscles & axial musculature of the neck)
Form the lateral vestibular nucleus to all spinal levels (forms lateral vestibulospinal tract)
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Vestibulo- autonomic control Radtke et al (2003), subjected patients to
abrupt head accelerationConcluded that a delayed increase of HR
in response to postural challenge occurred in patients with vestibular loss
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VESTIBULAR PROJECTIONS TO THALAMUSOriginate from rostral part of vestibular
nuclear complex Destined to VPL,VPM,VPI (ventrobasal
thalamus)Neurons respond to stimulation of deep
proprioceptors and joint receptors as well as vestibular inputs
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Vestibular-Hippocampal interactionsHippocampus thought to be nb for spatial
representation processes that depend on integration of both self movement & allocentric cues
Vestibular system is Nb source of self movement infoVarious parts of thalamus likely to transmit vestibular
information to hippocampus ?via parietal cortexMore direct pathways possible.Studies demonstrate the nb of vestibular hippocampal
interaction for hippocampal fxn, but also suggest hippocampus nb site for compensation of v. fxn following lesions (peripheral or central)
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?VESTIBULAR CORTEX?Does it exist?Different areas of primate cortex have been
named “vestibular”Guldin & Gurusser defined in 3 diff primate
series Similar pattern exist in humanArea 2v at tip of intraparietal sulcus, area 3v
in central sulcus, parietoinsular vestibular cortex next to post insula and area 7 in inferior parietal lobule involved in vestibular information processing
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VESTIBULAR SYSTEM & AGINGFalling & loss of balance among geriatric population
frequent & serious problemAttributed to the progressive deterioration of
anatomical components of vestibular systemStudy investigating quantitive diff in num, density or
type of hair cells or length of crista ampullaris in young & aged gerbils no diff found. Cause of vestibular dysfxn during aging should be looked for elsewhere.
Study regardign age related change in num of neurons in human vestibular ganglion proved that decline in prim neurons exist (anatomical basis of increased incidence of balance seen in age
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Origins of the Cranial Nerves
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Origins of the Cranial Nerves
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Good to know