The document summarizes the surgical anatomy of the inner ear. It describes the components of the inner ear as the bony labyrinth containing the vestibule, semicircular canals, and cochlea, and the membranous labyrinth containing the cochlear duct, utricle, saccule, and semicircular canals. It provides details on each of these structures, including their composition and functions. It also discusses the inner ear fluids of endolymph and perilymph, their ion concentrations, and theories about their formation and flow within the inner ear.

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SURGICAL ANATOMY
OF INNER EAR
Somnath Saha

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Components of inner ear
 Bony labyrinth
 Membranous labryinth

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Components of bony labyrinth
 Vestibule
 Semicircular canal
 Cochlea

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Bony labryinth

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Components of membranous labryinth
 Cochlear duct
 Utricle and saccule
 Semicircular canals
 Endolymphatic duct and sac

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Vestibule

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What does the vestibule have?
 Lateral Wall
 Contains oval window
 Medial Wall
 Spherical Recess
 Elliptical Recess
 Aqueduct of vestibule
 Posterosuperior part
 Openings of semicircular canals(5 in number)

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Semicircular canals
 3 in number
 Lateral
 Posterior
 Superior
 Lie at right angles to one another
 Each canal has an ampullated end and a nonampullated end
 Nonampullated ends of posterior and superior canals form a
common channel called crus commune

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Cochlea
 Consists of an osseous spiral lamina making 2.5-2.75 turns
around a centrally placed modiolus
 Modiolus divides the bony cochlea incompletely & gives
attachment to basilar membrane
 It has three parts
 Scala Vestibuli
 Scala Tympani
 Scala Media

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Cochlea

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Cochlea…continued
 Scala Vestibuli and scala tympani communicate via helicotrema
 Scala Vestibuli is closed by the footplate of the stapes and thus
is separated from the middle ear
 Scala tympani is connected to subarachnoid space via duct of
cochlea(next slide)

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Membranous labryinth

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Parts
 Cochlear duct
 Utricle and Saccule
 Three semicircular ducts

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Cochlear duct
 Other names:Scala Media/Membranous cochlea
 Appears triangular on cross section
 Three walls are:
 Basilar membrane
 Reissners’ membrane
 Stria vascularis
 Length of basilar membrane increases from basal coil to apical
coil:Hence low frequencies heard at apical coil,while high at
basal

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Utricle
 Lies in the posterior part of the bony vestibule
 Recieves five openings of the 3 semicircular ducts
 Connected to saccule via utriculosaccular duct
 Macula
 Sensory epithelium of utricle
 Concerned with linear acceleration and deceleration

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Saccule
 Lies in bony vestibule
 Anterior to utricle,opposite to stapes footplate
 Its macula(sensory epithelium) is also linked to linear
acceleration and deceleration

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Endolymphatic duct and sac
 Formed by union of ducts from saccule and utricle
 Terminal part dilated to form endolymphatic sac,which lies
between 2 layers of dura on posterior surface of petrous bone

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ENDOLYMPHATIC SAC
 It is a non sensory organ of inner ear
 Main functionare regulation of pressure and vol of endolymph
,the immune response of inner ear and the eiemination of
endolymphatic waste products by phagocytosis
 Functional alteration of these programme, ieading to deficient
endolymph haemostasis and/or altered immune response may
lead to MD

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Inner ear fluids
 Perilymph
 Endolymph

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Endolymph
 Fills entire membranous labyrinth
 Resembles ICF
 Rich in K+ ions
 Secreted by cells of stria vascularis+dark cells
 Flow:Two theories exist
 Longitudinal theory
 Radial theory

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Perilymph
 Resembles ECF in composition
 Rich in Na+ ions
 Communicates w/CSF via aqueduct of cochlea which opens into
the scala tympani
 Theories on perilymph formation:
 Blood serum filtrate formed by spiral ligament capillaries
 Direct continuation of CSF which reaches via aqueduct of cochlea

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Perilymph flow

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Thank you