Anatomy in description of internal ear

1. Dr. Ashly Alexander
RSO ENT 1st Year
Gandhi Medical College, Bhopal
ANATOMY OF INNER EAR

2. EMBRYOLOGY
Initially membranous labyrinth , followed by
encasement by bony labyrinth.
Starts within first few days( 22- 23 days)
3 main phases
1.Development (3-8thwk)
2.Growth (8-16thwk)
3.Ossification(16-24thwk)
2ANATOMY OF INNER EAR

3. Otic placode
Otic pit
Otocyst
Ventral saccular portion Dorsal uricular portion
Saccule & cochlear duct utricle,SCC &
endolymphatic duct
(forms earlier)
3ANATOMY OF INNER EAR

4. ANATOMY OF INNER EAR 4

5. ANATOMY OF INNER EAR 5

6. ANATOMY OF INNER EAR 6
!!! The organ of Corti differentiates from cells
along the wall of the cochlear duct.
6th wk
Neuroectoderm > spinal & vestibular ganglia &
corresponding sensory nerve
Mesoderm around otocyst >> otic capsule(ossifies
by 24th wk)
Bony labyrinth

7. ANATOMY OF INNER EAR 7
Vacoules containing PERILYMPH develop within otic
capsule >> perilymphatic space >>S.tympani & s.media
Last area to ossify???
FISSULA ANTE FENESTRUM
Embryology of ext & middle ear is diff from inner ear
They become interconnected by stapes footplate

8. CONGENITAL DEFORMITIES
ANATOMY OF INNER EAR 8
• Michels aplasia (CLA)- b/l absence of diff ear
structures with resultant anacusis.
• Mondini dysplasia- 1 ½ coils of cochlea
• Scheibe dysplasia- cochleosaccular dysplasia
• Alexander aplasia- aplasia of cochlear duct

9. AXIAL HRCT OF TEMPORAL BONE
ANATOMY OF INNER EAR 9
IAC
Cochlea
Vestibule
Post SCC

10. ANATOMY OF INNER EAR 10
MICHEL’S
APLASIA
MONDINI
DYSPLASIA

11. ANATOMY OF INNER EAR 11
ABIOTROPHY – degeneration of parts of auditory
apparatus
• Essentially ectoderm: of cochlear duct
(Waardenburg & Cogan syndrome)
• Essentially mesoderm: of sensory end organs
(Alport & Marfan syndrome)
• Essentially neuroectodermal: of nerve elements
(Von Recklinghausen’s syndrome)

12. INNER EAR (LABYRINTH)
ANATOMY OF INNER EAR 12
Labyrinth: a stucture
of winding passages
Location: petrous temporal bone

13. ANATOMY OF INNER EAR 13
Parts: Bony & membranous labyrinth

14. BONY LABYRINTH
ANATOMY OF INNER EAR 14
Bony Vestibule
SCC
Cochlea

15. VESTIBULE
ANATOMY OF INNER EAR 15
• Central part
• 5mm
• Situation
• Lateral wall: fenestra vestibuli(oval window)
• Medial wall: 2 recesses- Spherical R.(for saccule)
Elliptical R.(for utricle)
• Below Elliptical R- aqueduct of vestibule
• Posterosuperior part has 5 openings of SCC
• Perilymphatic cistern

16. BONY SCC
ANATOMY OF INNER EAR 16
3 in number
Superior / Anterior
Posterior
Lateral / Horizontal
Each .8mm diameter
Has dilatation at one end- ampula (containing crista)
2/3 rd circle
Lies in plane right angle to one another
Opens into vestibule by 5 orifices(d/t CRUS COMMUNE)
Involved in angular acceleration and balance

17. ANATOMY OF INNER EAR 17
SOLID ANGLE: area where 3 bony canals meet
• Superior SCC: 15-20mm, transverse to long axis of
petrous bone
• Posterior SCC: 18-22mm(longest),parallel
• Lateral SCC: 12-15mm(shortest), makes an angle of 30
with horizontal plane,
produces a bulge in the medial wall of middle ear
(SURGICAL LANDMARK FOR FACIAL N.),
FENESTRATION OPERATION

18. VESTIBULAR RECEPTORS & RELATION
TO HEAD MOVEMENT
ANATOMY OF INNER EAR 18
Superior SSC YES
Horizontal SSC NO
Posterior SSC SIDE TO SIDE

19. TRAUTMANN’S TRIANGLE
ANATOMY OF INNER EAR 19
• Bony labyrinth(ant)
• Sigmoid sinus(post)
• Dura containing sup petrosal sinus(sup)
Weakest part
Infections of temporal bone may traverse and
affect cerebellum.
Used as an approach to posterior cranial fossa lesions.

20. ANATOMY OF INNER EAR 20

21. COCHLEA
ANATOMY OF INNER EAR 21
• Snail shaped coiled tube
• Anterior part of labyrinth
• 2.5-2.75 turns round a central pyramid of bone
called MODIOLUS
• 35mm long
• PROMONTORY: d/t basal coil of cochlea
• Lined by Endosteum
• Contains perilymph & memb. labyrinth

22. MODIOLUS ?
ANATOMY OF INNER EAR 22
Central pyramid of bone around which cochlea forms
The base of modiolus directed towards internal
acoustic meatus
Transmits vessels and nerves to cochlea
Apex lies medial to tensor tympani muscle

23. OSSEOUS SPIRAL LAMINA ?
ANATOMY OF INNER EAR 23
• A thin plate of bone winds
spirally around modiolus
like the thread of a screw.
• This bony lamina gives
attachment to the basilar
membrane and divides the
bony cochlea tube into three
compartments.

24. ANATOMY OF INNER EAR 24
3 compartments of cochlea
• Scala vestibuli
• Scala tympani
• Scala media
HELICOTREMA
HELICOTREMA

25. ANATOMY OF INNER EAR 25
• AQUEDUCT OF COCHLEA- connects scala tympani
to subarachnoid space
-regulates perilymph & pressure in bony labyrinth
-contains PERIOTIC DUCT (reticular network of
connective tissue)

26. MEMBRANOUS LABYRINTH
ANATOMY OF INNER EAR 26
A continuous series of membranous sacs and ducts
within the bony labyrinth
Contains ENDOLYMPH
Parts
1. Pars superior/vestibular labyrinth- saccule, utricle
& memb SCC
2. Endolymphatic sac & duct
3. Pars inferior/ductus cochlearis- scala media

27. ANATOMY OF INNER EAR 27

28. UTRICLE
ANATOMY OF INNER EAR 28
• Bigger than saccule
• Occupies elliptical recess
• Post wall- contains openings of 3 SCC
• Ant wall-connects to saccule via endolymphatic
duct
• Receptor organ-MACULA
• Utriculoendolymphatic duct allows only inflow of
endolymph

29. SACCULE
ANATOMY OF INNER EAR 29
• Lies in front of utricle
• Occupies spherical recess
• Connected to cochlear labyrinth via DUCTUS
REUNIONS
• Receptor organ-MACULA

30. ENDOLYMPHATIC DUCT
ANATOMY OF INNER EAR 30
• Contains initial dilatation called SINUS before
entering bony vestibular aqueduct.
• Enlarges again beyond isthmus
• Proximal portion is rugose & distal smooth
• Distal smooth portion is contained within dura
• Ends close to sigmoid sinus
• Exposed for drainage or
shunt operation in
MENIERE’S DISEASE

31. LARGE VESTIBULAR AQUEDUCT
SYNDROME
ANATOMY OF INNER EAR 31
Enlarged vestibular aqueduct asso. with SNHL,
Pendred syndrome & anatomical defect of cochlear
modiolus

32. DONALDSON’S LINE
32
• Surgical landmark for ENDOLYMPHATIC SAC.
• Passes through horizantal SSC bisecting posterior
SSC. The endolymphatic sac that appears as
thickening of post cranial fossa dura is situated
INFERIOR to Donaldson’s line.

33. ANATOMY OF INNER EAR 33

34. MEMBRANOUS SEMICIRCULAR DUCTS
ANATOMY OF INNER EAR 34
• 3 in number
• Right angled to each other, hence represent 3
planes of space
• Dilates into AMPULLA at one end(2mm)
• Attached to outer wall by delicate fibrous
strands
• Receptor organ in ampulla- CRISTA

35. ANATOMY OF INNER EAR 35
Anterior and posterior canals are vertical
Lateral canals of both sides are
horizontal
Stimulation of semicircular canals produce
NYSTAGMUS
• Nystagmus is horizontal due to horizontal canals,
rotatory due to superior canals & vertical due to
posterior canals

36. VESTIBULAR RECEPTOR ORGANS
MACULA
ANATOMY OF INNER EAR 36
• Saccule(lies vertically) & utricle(lies horizontally)
• Composed of:
Hairs cells, supporting cells & gelatinous mass
(mucopolysaccharides)
• In macula- additional calcium carbonate crystals
called OTOLITH or STATOCONIA

37. ANATOMY OF INNER EAR 37

38. VESTIBULAR RECEPTOR ORGANS
CRISTA
ANATOMY OF INNER EAR 38
• In ampulla
• Contains hair cells, supporting cells & gelatinous
mass
• Dome shaped gelatinous
mass called CUPULA

39. HAIR CELLS
ANATOMY OF INNER EAR 39
Type 1 Hair cells
• flask shaped
• With nerve chalice
• Afferent N. terminal
forms a calyx
• Efferent N. terminal
end on calyx
Type ll Hair cells
 cylindrical shape
 Without nerve chalice
 Both afferent & efferent
terminate without
forming calyx on the cell
body

40. ANATOMY OF INNER EAR 40

41. ANATOMY OF INNER EAR 41
Sensory hair protrude from each hair cell
1 Kinolcilium
Many Stereocilia
Decreases in length as distance from kinocilium
increases
Stimulus : shearing motion of cupula & statoconial
memb. >> mech energy in hair cell >>action
potential in nerve fibres
Flock & Wersall(1963)
Depolarization(towards kinocilium)
Hyperpolarization (away from kinocilium)

42. ANATOMY OF INNER EAR 42
• Lindeman (1969):
In ampullary crista cells are polarised in 1
direction
ie, towards utricle (horizontal SCC)
away from it (sup & post SCC)
In macula an arbitrary
line divides 2 areas(striola)

43. ARRANGEMENT OF STEREOCILIA
ANATOMY OF INNER EAR 43
• Each row of stereocilia is taller than the next.
The tip of each stereocilium is linked to the
side of the stereocilium behind it by a tip link.

44. MEMBRANOUS COCHLEA
ANATOMY OF INNER EAR 44
• Triangular
• Floor: Basilar membrane
• Roof: Reissner’s membrane
• Laterally: stria vascularis & bony wall of cochlea
• Basilar memb-supports organ of corti
thin inner part(zona arcuata)
thick outer part(zona pectinata)
• Tectorial memb-gelatinous matrix with delicate fibers
shearing force between hair cells
produces stimuli.

45. ANATOMY OF INNER EAR 45
•

46. ORGAN OF CORTI
ANATOMY OF INNER EAR 46
• Sense organ of hearing
• Rests on basilar memb
• Contains : sensory cells, supporting cells &
overlying gelatinous tectorial membrane
• Single row of inner(4500) & 3 rows of outer
hair cells(12500)
• Tunnel of corti- cortilymph
• Inner hair cell ~ type 1 cells
• Outer hair cells ~ type 2 cells

47. ANATOMY OF INNER EAR 47

48. ANATOMY OF INNER EAR 48
Characteristics Outer hair
cells
Inner hair
cells
Number 12,000 3500
Location Farther from
Modiolus
Nearer to
Modiolus
No. of rows 3-4 1
Shape of hair cells Cylindrical Flask shape
No. of rows of cilia 6-7 per cell 2-4 rows per
cell
Steriocilia arrangement W or V shape Shallow U
shape
Length of steriocilia Long & thin Short & fat
Motility Motile Non motile

49. ANATOMY OF INNER EAR 49
Characteristics Outer hair cells Inner hair cells
Nerve supply Primarily efferent Mainly afferent
Development Develop late Develop earlier
Function Modulate
function of inner
hair cells.
Transmit auditory
stimulus
Vulnerability Easily damaged
by ototoxic drugs
& high intensity
Noise.
More resistant to
ototoxic drugs &
high intensity
Noise.
Otoacoustic
emissions
Generates
otoacoustic
emissions
No generation of
otoacoustic
emissions.

50. ANATOMY OF INNER EAR 50

51. SPECIAL TYPES OF CELLS IN ORGAN OF CORTI
ANATOMY OF INNER EAR 51
• BOETTCHER’S CELLS: Present only in the lower
turn of the cochlea Lie on the basilar membrane
beneath Claudius' cells Supporting cells for the
auditory hair cells in the organ of Corti.
• CLAUDIUS’ CELLS: Located above Boettcher's cells
Supporting cells for the auditory hair cells in the
organ of Corti Contain a variety of aquaporin water
channels involved in ion transport play a role in sealing
off endolymphatic spaces
• HENSENS CELLS: High columnar cells that are directly
adjacent to the third row of Deiters’ cells.

52. ANATOMY OF INNER EAR 52
• HENSEN’S STRIPE: Section of the tectorial
membrane above the inner hair cell.
• NUEL’S SPACE: Fluid filled spaces between the
outer pillar cells and adjacent hair cells. Also the
spaces between the outer hair cells.
• HARDESTY’S MEMBRANE: Layer of the tectoria
closest to the reticular lamina and overlying the
outer hair cell region.
• ROSENTHAL CANAL: Spiral ganglion are situated in
Rosenthal canal, which runs along osseous spiral
lamina

53. RETICULAR LAMINA
ANATOMY OF INNER EAR 53
• The reticular lamina is a solid surface at the
tops of the hair cells, so the tops of the hair
cells are in endolymph and the bottom of the
hair cells are in perilymph

54. FREQUENCY REPRESENTATION
ANATOMY OF INNER EAR 54
• length of basilar membrane increases as we
proceed from basal coil to apical coil

55. 55
PERILYMPH ENDOLYMPH
Resembles ECF Resembles ICF
Present in scala tympani and scala
vestibuli
Present in scala media
Major cation is Na Major cation is K
Has potential of 0 mV Has potential of 80mV
Also c/a Cotunnius’ liquid Also c/a Scarpa's liquid
SOURCE:2 theories
1)filtrate of blood serum from
capillaries of spiral ligament.
2)CSF reaching labyrinth via
aqueduct of cochlea.
SOURCE:2 theories
1)filtrate of blood serum from
capillaries of spiral ligament.
2)CSF reaching labyrinth via
aqueduct of cochlea.
Perilymph and endolymph participate in a unidirectional flow
that is interrupted in Ménière's disease.

56. AUDITORY NERVE
ANATOMY OF INNER EAR 56
• The dendrites contact the hair cells. The cell
bodies form the SPIRAL GANGLION, and the
axons form the auditory nerve that connects the
ear to the brainstem.
• The “contact” points between the dendrites and
the hair cells or between the axons of one
neuron and the dendrites of another are called
synapses.

57. ANATOMY OF INNER EAR 57
• The neurons are two
type
• 1)type-1 majority
spiral ganglion neuron
(95%)
• Innervated inner hair
cell in convergent
manner
• Peripheral process of
type 1 spiral ganglion
neuron form synapse
with inner hair cell base
and unmyelinated
TYPE1
TYPE 2

58. ANATOMY OF INNER EAR 58
Type- ll neurons of
spiral ganglion
innervated the outer
hair cells in a divergent
manner
Their peripheral process
and central axons are
unmyelinated
Each Peripheral process
before branching to
innervate up to ten
outer hair cell
TYPE1
TYPE 2

59. ANATOMY OF INNER EAR 59
It enter the organ of corti through a hole in
upper border of spiral lamina – FORAMEN
NERVOSUM and approach to inner hair cell by
HABENULA PERFORATA
Central process enter the modiolus, projects to
cochear nucleus ,are myelinated.
Low frequency fibers occupy the center of
auditory nerve (coming from apex of cochlea) and
fibers of higher frequency found towards the
periphery(coming from base of cochlea)

60. PATTERN OF EFFERENT INNERVATION
ANATOMY OF INNER EAR 60
• 95% of Type- I Fibres innervate Inner hair cells
and provide sensory innervation
PATTERN OF AFFERENT INNERVATION
• Majority of efferent innervate OHCs, and the
contacts on OHCs differ from those on IHCs.
Efferents form large calyx-shaped contacts on
the OHC cell body; efferents form small bouton-
like contacts on the afferent nerve fibers that
contact IHCs.

61. CENTRAL AUDITORY PATHWAY
Cochlear nerve from
cochlea to cochlear
nucleus in brain
stem
Auditory nerve splits
into two streams one
which goes to the
ventral cochlear
nucleus & the other to
the dorsal nucleus
61ANATOMY OF INNER EAR

62. CENTRAL AUDITORY PATHWAY
62

63. CENTRAL AUDITORY PATHWAY
Dorsal nucleus : Analyse the quality of sound, picking
apart the tiny frequency differences
Ventral nucleus : Analyse loudness of sound
Efferent are derived from the superior colliculus and
make direct connection with outer hair cells
63ANATOMY OF INNER EAR

64. VESTIBULAR PATHWAY
• First order neurone is bipolar in nature
• Body or soma is in the Scarpa’s ganglion
Situated in internal auditory meatus
• The dendrites of the bipolar cells reach
the receptor organs in the crista ampularis
and macula
• The axons form the vestibular division of
vestibular cochlear nerve
64ANATOMY OF INNER EAR

65. VESTIBULAR NUCLEI
• Four vestibular nuclei in the medulla oblongata
• Superior, inferior, lateral and medial
• Most of the vestibular fibres coming from crista
ampularis of semicircular canals reach superior and
medial nuclei
• Lateral vestibular nuclei receives the fibres mostly
from the maculae of otolith organs
• The inferior vestibular nuclei receives fibres from
both the crista ampularis and maculae
65ANATOMY OF INNER EAR

66. • The fibres from some bipolar cells reach
cerebellum directly and terminate in the
floculonodular lobe or the fastigial nucleus in
the cerebellum
• The efferent fibres to hair cells provide
tonic inhibition of hair cells
66ANATOMY OF INNER EAR

67. SECOND ORDER NEURON
1. Vestibulo ocular tract
This tract is concerned with movements of eyeballs in
relation to the position of the head
2. Vestibulo spinal tract
This tract is involved in reflex movements of head
and body during postural change
3. Vestibulo reticular tract
These fibres are concerned with facilitation of muscle
tone
4. Vestibulo cerebellar tract
Involved in coordination of movement acc. to body
position
67ANATOMY OF INNER EAR

68. • Acoustic neuroma also called vestibular
schwannoma
• It is arises from the schwann cells of the
vestibular division of 8 C.N with in the internal
auditory canal
68ANATOMY OF INNER EAR

69. BLOOD SUPPLY OF LABYRINTH
ANATOMY OF INNER EAR 69

70. ANATOMY OF INNER EAR 70
Remember!!!
Cochlea does not have any collateral
arterial circulation

71. VENOUS DRAINAGE OF LABYRINTH
ANATOMY OF INNER EAR 71
Mainly by:
• Internal auditory vein
• Vein of cochlear
aqueduct
• Vein of vestibular
aqueduct
These Drain into inferior
petrosal and sigmoid
sinuses.

72. INTERNAL AUDITORY CANAL
ANATOMY OF INNER EAR 72
About 1 cm long
Passes into petrous part of temporal bone in a
lateral direction
Lined by dura
At its lateral end (fundus) IAC is closed by a
vertical cribriform plate of bone that seperates
it from labrynth

73. INTERNAL AUDITORY CANAL
ANATOMY OF INNER EAR 73
Contents:
 Vestibulocochlear
Nerve
 Facial nerve including
nervus intermedius
 Internal auditory
artery and vein

74. BONY LABYRINTH
COCHLEAR IMPLANT

75. COCHLEAR IMPLANT

76. COCHLEAR IMPLANT