Anatomy of inner ear

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.