1. The inner ear consists of the bony labyrinth within the temporal bone and the membranous labyrinth contained within. 2. The bony labyrinth is composed of the vestibule, semicircular canals, and cochlea. The membranous labyrinth contains the cochlear duct, utricle, saccule, and semicircular ducts filled with endolymph. 3. Within the cochlea, the organ of Corti transduces sound into electrical signals via inner and outer hair cells. The hair cells sit on the basilar membrane and are stimulated by the overlying tectorial membrane.

1. Anatomy Of Inner
EAR
Presenter-Dr.Razal M Sherif
Moderator-Dr.Joythi Swarup.R

2. Questions in previous Presentation
Malleus
o Weight-23mg
o Length-9mm
Incus
o Weight-25-30 mg
o Length of long process -7 mm
o Length along short process-5mm
Stapes
o Weight-2.86 mg
o Height-3.26 mm

3. Inner Ear/Labyrinth
• Development of Inner ear starts by 3rd week of IUL and
completes by 16th week.
• Cochlea sufficiently developed by 20th week (fetus can
hear in the womb)
• Lies in the petrous part of the temporal bone.
• Is an important organ of hearing and balance.
• 2 Parts
• Bony Labyrinth
• Membranous Labyrinth

4. Bony Labyrinth
• Vestibule
• Cochlea
• Semicircular Canals

5. Vestibule
• Small Ovoid bony chamber measuring 4mm
• situated between
o Laterally - Medial wall of the middle ear
• is the opening of the oval window which is closed by the
footplate of the stapes
o medially - by Internal auditory meatus .
• Medially(inner Surface)-2 recesses
o Spherical recesses-lodges the sacule
o Elliptical recesses-lodges the utricle
• Below elliptical recesses-opening of endolymphatic duct
• Postero superior
o 5 openings of SCC

7. Semi Circular Canals
• 3 semi circular canals
o Superior
o Posterior
o Lateral
• They lie in planes at right angle to each other.
• Each canal got ampullary end ,which open in the
vestibule.
• Non-ampullary end of Lateral SCC open
independently
• Post. SCC and Sup. SCC form a common opening
Called CRUS COMMUNE

9. Cochlea
• Coiled tube – 35mm.
• Two and half turns around a central bone called
Modiolus
MODIOLUS
• Pyramidal Shaped
• Base directed towards Internal Acoustic Meatus
• Vessels and Nerves enter cochlea via modiolus
• Around modiolus -thin plate of bone winding spirally
is a called – Osseous Spiral lamina

11. • The Osseous Spiral lamina divides the bony cochlea
(incompletely) into
o Scala Vestibuli
o Scala Tympani.
• And gives attachment to a membrane called
Basilar membrane.
• Above the Osseous Spiral lamina and the Basilar
membrane lies the Scala Media which contains the
endolymph and Organ of Cori.

13. • The scala vestibuli and scala tympani are filled with
perilymph and communicate with each other at
the apex of cochlea through an opening called
HELICOTREMA
• Scala vestibuli
o closed by the foot plate of stapes
• scala tympani
o Closed round window membrane (secondary tympanic
membrane)
• Connected to Sub arachnoid space by aqueduct
of choclea

16. Membranous Labyrinth
• It lies within the bony labyrinth
• Filled with Endolymph.
• Space between membranous
labyrinth and bony labyrinth-
Perilymph.
• It contains
o Cochlear Duct
o Utricle and Saccule(otolith organs)
o Semi circular Duct
o Endolymphatic Duct and Sac

17. Cochlear duct
• It is a blind coiled tube.
o called as Scala Media/membranous cochlea
• It appears triangular on cross-section-
o One wall of triangle is the basilar membrane
o Another wall of triangle is the Reissner's membrane
o And the third wall is the stria vascularis,
• Cochlear duct is connected to the saccule by
Ductus reuniens

19. • Utricle
o lies in the posterior part of bony vestibule.
o It receives the five openings of the three semicircular ducts.
o It is also connected to the saccule through utriculosaccular
duct.
o sensory epithelium of the utricle is called the macula
• Saccule
o Lies anterior to urticle
o sensory epithelium of the saccule is called the macula
o Responds to linear acceleration and deceleration
o In Meniere’s disease –distented saccule lies against stapes
foot plate

20. • Semicircular ducts.
o three in number and correspond exactly to the three bony
canals.
o They open in the utricle.
o The ampullated end of each duct contains a thickened
ridge of neuroepithelium called crista ampullaris.

21. • . Endolymphatic duct and sac.
o the union of two ducts, one each from the saccule and
the utricle.
o It passes through the vestibular aqueduct.
o Its terminal part is dilated to form ENDOLYMPHATIC SAC
which lies between the two layers of dura on the posterior
surface of the petrous bone.

22. Fluid System
• Perilymph
o Present in btw memb. Labyrinth and bony labyrinth
o Present in inside the scala vestibuli and Scala tympani
o Rich in sodium (Na+)
o Like extra cellular fluid
o It communicates with CSF through the aqueduct of
cochlea.
o Formation of perilymph:
• It is a filtrate of blood serum and is formed by capillaries of the
spiral ligament
• a direct continuation of CSF and reaches the labyrinth via
aqueduct of cochlea.

23. • Endolymph
o fills the membranous labyrinth
o resembles intracellular fluid,
o rich in Potassium (K+) ions.
o It is secreted by
• secretory cells of the stria vascularis of the cochlea
• the dark cells (present in the utricle and the ampullated
ends of semicircular ducts) .

24. Composition of inner ear
fluids

25. ORGAN OF CORTI
• Organ of hearing,
• Situated on basilar membrane of cochlea
• 3 parts
o Sensory Hair cells
o Supporting cells
o Tectorial Membrane

26. Hair Cells
• Transduce sound energy to Electrical Energy.
• 1 row of flask shaped inner hair cells
• 3 or 4 rows of cylindrical shaped outer hair cells.
• Situated around the tunnel of corti

28. Inner Hair cells Outer Hair cells
• Total No : 3500
• Arranged in single row
• Flask shaped
• 95% afferent from
Cochlear nerve (8th
CN)
• Stereocilia arranged in
V or W format
• More resistent
• Transmit auditory stimuli
• 12,000 [ 1:4 ratio]
• Multiple rows
• Cylindrical
• Efferent from Sup.
Olivary complex
• Stereo cilia single
continous layer.
• Easily damaged to
drugs & loud sound
• Modulate the IHC.

29. Supporting cells
• Stabilize and support the organ of corti
• Supply nutrient to the highly specialized sensory
cells(inner and outer hair cells)
• Includes
o Hensen's Cell
o Claudius Cells
o Deiters Cells
o Boettcher’s Cell

30. Tectorial Membrane
• It over hangs the organ of corti
• Gelatinous – Spread over the hair cells.
• The shearing force between Hair cells and Tectorial
membrane produces the stimulus in hair cells.

32. Cristae
Crista Ampullaris
• Seen in the ampullated end
of 3 SCC
• thickened ridge - covered
by a gelatinous matrix
called Cupula
• Two type of hair cells
• Type 1 – Flask shaped
• Type 2 – Cylindrical
• The cilia of sensory hair cells
are present in cupula.

33. Maculae
• Located in otolith organs
• Sense the position of Head
in response to gravity
• Hair cells
• Type 1
• Type 2
• Supporting cells
• Otolithic membrane
• Gelatinous layer
• Otoconia [Ca(CO ) ]
• Cilia of hair cells in gelatinous
layer – Senses linear,
gravitational & head tilt
movements.
•

34. Ant. Inferior Cerebellar
Art
Labyrinthine/Intern
al Auditory art.
Ant.
Vestibular
A
(to utricle &
LSCC, SSCC)
Common
Cochlear
Vestibulo
Cochlear
Main Cochlear
80%
Cochlear
branch
(20%)
Post. Vestibular
A
(to saccule & PSCC)
Blood Supply
Arterial

35. Venous Drainage
• 3 Veins
o Internal auditory vein
o Vein of cochlear aqueduct
o Veins from the vestibular aqueduct

36. Applied Anatomy
Presbycusis
o Sensory hearing loss associated with physiological ageing
process in ear.
o 4 Pathological type
• Sensory-degenaration of organ of corti
• Neural-degenartion of spiral ganglion
• Straial-Atropy of stria vascuaris
• Cochlear-Stiffing of Basilar membrane
Noise induced hearing loss
o Damages the Hair cell-outer hair cells are affected more

37. Ototoxicity
o Damage inner ear and cause SNHL,Tinnitus and vertigo.
o Aminoglycoside-destroy type-1 hair cell in crista Ampularis and
outer hair cells.
o Diuretics-edema and cystic changes in stria Vascularis.
o Quinine-causes vasoconstriction of small vessels of cochlea and
stria vascularis.
o NSAIDs-Piroxicam,Ketorolac
Meniere’s disease(Endolymphatic Hydrops)
o Endolymphatic distention mainly in scala media,saccule,Utricle
o Leads to bulging of Reissner’s Membrane and saccule and
utricle.