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ANATOMY OF INNER EAR
Dr. Supreet Singh Nayyar, AFMC
for more presentations, visit www.nayyarENT.com
20-07-2012
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• Organ concerned with hearing and balance
• Consists of : a) Bony Labyrinth b) Membranous
Labyrinth
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BONY LABYRINTH• Consists of :
a)Vestibuleb)Semicircular
Canals c) Cochlea
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SALIENT FEATURES
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MEMBRANOUS LABYRINTH
• Consists of : a) Cochlear Duct b) Utricle & Saccule c) Semicircular
Ducts d) Endolymphatic
duct & Sac
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STRUCTURE OF THE COCHLEAR
DUCT
Subdivided into: • Scala tympani,
Scala vestibuli & Scala media
• Scala media is triangular in cross section
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REISSNER’S MEMBRANE
• Separates Scala media from Scala tympani
• Runs obliquely• Extends from spiral
limbus to lateral wall
• Consists of 2 layers of cells separated by basement membrane 20-07-2012
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BASILAR MEMBRANE• Acellular layer• Stretches from osseous spiral lamina to the spiral
prominence• Organ of Corti is situated on the upper surface• Stretches from spiral limbus to Claudius cells • Below it lie spindle shaped cells (tympanic cells)
& a branching spiral vessel
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SPIRAL LIMBUS• Composed of interdental cells & main body of
connective tissue cells & blood vessels embedded in an ECM
• Concave side forms the Inner Sulcus
• Convex surface forms Tectorial membrane
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STRIA VASCULARIS• Forms the lateral
boundary• Composed of 3 layers
of cells: Marginal cells Intermediate cells Basal cells• Spiral ligament
(fibrocytes & connective tissue) on the outer side
• Contains a variety of ion pumps, enzymes & transport proteins
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CELLULAR ARCHITECHTURE AND
FUNCTION OF ORGAN OF CORTI
• Sensory region consists of 2 types of sensory hair cells with apical stereocilia
• Stereocilia project into the overlying endolymph
• Inner hair cells form a single row while outer hair cells form 3-4 rows
• Separated by 2 rows of pillar cells from the Tunnel of Corti 20-07-2012
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SUPPORTING CELLS• Associated with hair cells• Inner phalangeal cells & border cells enclose
inner hair cells• Deiters’ cells enclose outer hair cells & send
phalangeal processes to the adjacent cells• Hensen’s cells & Claudius’ cells are present on
the outer edge of basilar membrane
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OUTER HAIR CELLS• Cylindrical cells with
flattened upper surface• Sensory upper end &
synaptic pole at basal end
• Stereocilia arranged in V or W shaped rows
• In contact with the undersurface of tectorial membrane
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STEREOCILIA• Cylindrical• Bevelled tip with narrow ankle
region• Angled towards each other• Connected by tip links &
lateral links• Membrane contains proteins
associated with calcium control & mechanosensitivity
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INNER HAIR CELLS• Flask shaped• Flattened or concave
apical surface• 3-4 linear rows of
stereocilia• Cell bodies are rich in ER,
golgi bodies, mitochondria,
• Synaptic pole at the basal end
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ULTRASRUCTURE OF SUPPORTING
CELLS
• Phalangeal processes: microtubular bundles• Deiters’ cell cup: Actin- rich core• Inner phalangeal & border cell membranes:
associated with IHC membranes• Finger-like projections: interdigitate with
afferent nerve auditory nerve fibres• Pillar cells: Thick microtubular bundles with
radial feet & arching above
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INNERVATION OF ORGAN OF CORTI
• Acoustic information from hair cells is transferred by the auditory portion of the VIIIth nerve to the ipsilateral cochlear nuclear complex in the brain stem
• Composed of afferent fibres from spiral ganglion neurones
• Types of Neurones: Type I and II
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ANATOMY AND ULTRASTRUCTURE
OF THE VESTIBULAR ORGAN • Delicate system of membranous ducts containing
sensory epithelia or machanoreceptors• Important for the sense of gravity and balance • Sensory epithelium located in the 3 ampullae,
semicircular canals and in the maculae of saccule and utricle
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FUNCTIONS OF HUMAN
VESTIBULAR
ORGAN
Human Vestibular Labyrinth Function
Receptor for Gravitation & other Linear Accelerations
Receptor for Angular
Accelerations
Regulates Tonus of BodyMusculature
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UTRICLE
• Oblong & irregular; superior to the saccule• Slopes anteriorly upwards at an angle of 30 degrees• Macula utriculi lies in a horizontal plane• Mean area: 4.30 mm²• Contains approx. 33,000 hair cells
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SACCULE• Hook shaped• Lies virtually in a vertical position• Mean area of saccular macule: 2.4 mm²• Contains approx.18,000 hair cells• Overlying the neuroepithelium is a calcareous
material consisting ‘otoconia’• Partially anchored in a gelatinous substance
forming otoconial membrane• Hair processes of sensory cells project into it
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OTOCONIAL LAYER• Gelatinous layer, a subgelatinous space and
otoconia• Consists of an organic protein matrix along with
inorganic calcium carbonate crystallized in the form of ‘calcite’
• Secreted from apical cytoplasm of adjacent supporting cells with CA
• Degenerative changes with aging & disease• Otoconial turnover occurs with the help of ‘dark
cells’
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SRUCTURE AND FUNCTION OF
THE AMPULLA AND CUPULA
• Superior opening of horizontal & superior semicircular canal, and inferior opening of posterior canal widen to form Ampulla
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VESTIBULAR SENSORY CELLS
TYPE I CELLS:• Flask shaped• Surrounded by nerve
chalice• Collateral extensions on
Type II cellsTYPE II CELLS:• Synapse with the
collaterals & with the membranes of the chalices
• Cylindrical 20-07-2012
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VESTIBULAR NERVE• Contains approx. 18,000 afferent fibres• Vestibular ganglion or Scarpa’s ganglion consist
of bipolar neurons• Consists superior & inferior groups of cells
associated with superior & inferior vestibular nerve.
• Nerves contain both large & small fibres• Vestibular & cochlear nerves merge in the IAM• Human vestibular nerve contains efferent fibres
supplying both the cochlear & vestibular sensory organs
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VASCULAR SUPPLY OF LABYRINTH
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THANK YOU
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