ANATOMY & EMBRYOLOGY OF VESTIBULAR SYSTEM

S Pandey

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

EMBRYOLOGY

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

The Semicircular Canals

UTRICLE & SACCULE

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.

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

Vestibular hair cellsType 1 & 2Sensory cellsStereociliaKinociliumSupporting cells

BLOOD SUPPLY

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

Vestibular nerveBranches into

superior division that innervates the ant & horizontal cristae ampullares and utricular macula

Inferior division that innervates post crista ampullaris & saccular macula

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

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

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

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

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)

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)

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

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

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)

?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

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

Origins of the Cranial Nerves

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Origins of the Cranial Nerves

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