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ANATOMY OF INNER EAR

Dr. Supreet Singh Nayyar, AFMC

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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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