BASICS OF INNER EAR ANATOMY

1. Anatomy of Inner ear
DR YATISH KUMAR B L
MS ENT
PG/JR 1

2. Inner Ear
Consists of an irregular
system of canals
and cavities:
 Bony labyrinth
 Membranous
labyrinth

3. Bony labyrinth: Hard, bony
outer shell.
Membranous labyrinth: Fully
contained inside the bony
labyrinth.

4. Bony labyrinth
 Vestibule – central
chamber of labyrinth.
In its lateral wall lies
the oval window.
 Semicircular canals.
 Cochlea.

5. Membraneous labrynth
 Cochlear duct
 Utricle
 Saccule
 Three semicircular
canals
 Endolymphatic duct and
sac

6. Utricle
 Posterior part of
vestibule.
 5 openings of
semicirular ducts.
 Macula
 Utricosaccular duct.

7. Saccule
 lies anterior to utricle
opposite the stapes
footplate in the bony
vestibule.
 Saccule is connected
to the cochlea via a
thin reunion duct.

8. Semicircular ducts
 3 in number.
 Open into utricle
 Crista ampularis

9. Crista ampullaris

13.  Macula is a gelatinous matrix into which hair cells project
and which is studded with tiny calcium carbonate
granules called otoconia.

15. Arrangement of stereocilia
 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.

16. Hair cells
type 1 type ll

17. Types of Hair cells
 Type 1 Hair cells = flask
shaped cells with a rounded
base, narrow neck.
 Nucleus is basal, surrounded
by mitochondria
 With supranuclear Golgi
complex, occasional cisternae
of RER & small vesicles.
 With 50-100 sterocilia on free
surface. Tallest hair is 10um
near kinocilium & shortest is
1um on the opposite side.
 Type ll Hair cells = more
columnar, kinocilium, sterocilia,
cytoplasmic roganelles are
similar to type 1.
 Golgi complex is larger, small
vesicles found in great
numbers in cytoplasm.
 Synaptic ribbons are found in
the peripheral cytoplasm
opposite the plasmalemma of
terminal boutons.
 Some endings contain clear
synaptic vesicles (non
granulated vesicles) carry
afferent nerves info to brain.

18. Semicircular Canals
 Three semicircular
canals-
 Lateral (Horizontal)
 Superior ( Anterior
vertical)
 Posterior ( Posterior
vertical)

19. Horizontal semicircular canal
 The lateral or horizont
al canal (external
semicircular canal) .
 shortest of the three
canals.
 Movement of fluid
within this canal
corresponds to
rotation of the head
around a vertical axis
(i.e. the neck).

20.  Projects as rounded bulge in middle ear, aditus &
antrum
 Makes an angle of 30 with horizontal plane.
 It measures from 12 to 15 mm., and its arch is
directed horizontally backward and laterally; thus
each semicircular canal stands at right angles to
the other two.

21. Superior semicircular canal
> detects rotation of the
head around a rostral-
caudal (anterior-
posterior) axis, or in
other words rotation in
the coronal plane.
> example, when you
move your head to
touch your shoulders.
>15 to 20 mm in length,
is vertical in direction.

22.  Its lateral extremity is
ampullated, and
opens into the upper
part of the vestibule;
the opposite end joins
with the upper part of
the posterior canal to
form the crus
commune, which
opens into the upper
and medial part of the
vestibule.

23. Posterior semicircular canal
 The posterior
semicircular
canal detects
rotations of the head
in around the lateral
axis. This occurs, for
example, when
nodding your head.

24.  It detects rotations of
the head in
the sagittal plane.
 Nodding of head.
 18 to 22 mm.

25. Semicircular Canals
 The angle formed by three semicircular canals is the Solid angle.

26. Trautmann’s triangle.
 The triangle bounded by the bony labyrinth, sigmoid
sinus, and superior petrosal sinus is known as
Trautmann’s triangle.

27. Cochlea
 Snail shaped coiled tube.
 2.5 to 2.75 turns round a
central pyramid of bone
called modiolus.
 30 mm long
 5 mm from base to apex & 9
mm around its base Anterio
medial to vestibule.

28. Modiolus
 Central pyramid of
bone around which
cochlea forms
 The base of modiolus
directed towards
internal acoustic
meatus
 Transmits vessels and
nerves to cochlea

29. Promontary
A bony bulge in
the medial wall of
middle ear ,
represents the
basal coil of
cochlea.

30. Vestibule
 Central chamber
 Spherical recess-
saccule
 Ellipticle recess-utricle

31. Osseous spiral lamina
 A thin plate of bone
winds spirally around
modiolus .
 This bony lamina gives
attachment to the
basilar membrane and
divides the bony
cochlea tube into three
compartments.

32.  Basilar membrane =
thin sheet extending
from spiral lamina to
spiral ligament of
cochlea. Movement of
the the basilar
membrane by pressure
changes induced by
stapes footplate motion
at the oval window

33.  Vestibular membrane
= 2nd partition from soft
tissue ridge of spiral
lamina to the spiral
ligament.
• Reissner’s membrane
= outer surface of
vestibular membrane,
lined by thin squamous
perilymphatic cells.

34.  Lumen of cochlear
canal is partitioned into
3 spiral chambers:
1. scala vestibuli
(above)
2. scala media
(between)
3. scala tympani (below)

35. Rosenthal’s canal
 Spiral ganglions are
situated in this canal
which runs along the
osseous spiral lamina.

36. Scala vestibuli
 This uppermost
channel is
continuous with
vestibule and closed
at oval window by
stapes footplate

37. Scala tympani
 This lowermost channel is
closed by secondary TM
of round window

38. Scala media
 Bind coiled tube,
connected to the
saccule via ductus
reunions.

39. Helicotrema

40. Aqueduct of cochlea
 Scala tympani is
connected with
subarachnoid
space via
aqueduct of
cochlea.
 It is thought to
regulate perilymph
& pressure in
bony labrynth

41. Basilar membrane
>Has 2 zones:
Zona arcuata = thin,
extends from
medial attachment
to base of outer
most cells of organ
of Corti. Supports
the organ of Corti.
Zona pectinata=
thicker from organ of
Corti to spiral
ligament.

42. Tectorial membrane
 Secreted at the
upper surface of
interdental cells,
forms a cuticular
layer over these
cells
 Composed of fine
filaments embedded
in gelatinous matrix
rich in
mucopolysaccharide
s.

44. Organ Of Corti
 The end organ of
hearing
 Inner hair cells -
broad base, resting
on the basilar
membrane, slender
and conical, nucleus
is basal.
 Outer hair cells -
longer and more
oblique, leaning to the
inner pillars.with
broad thin base.

45.  Tunnel of corti-
wide triangular
intercellular space
continuous through
cochlear length.
Bounded above
converging inner
and outer pillar cells.

46.  Deiters cells -the
supporting cells for
the 3 -4 rows of
outer hair cells.
Base is columnar
with cup shaped
upper end. The apex
does not reach the
free surface of the
organ of Corti.

47.  Inner phalangeal cells - arranged in a row on the inner side of the
inner pillar cells. Contiguous with slender Border cells marking the
inner boundary of the organ of corti. Lining epithelium is low cuboidal
or squamous cells.
 Cells of Hensen - delimit the outer border of the organ of Corti
arrange in rows decreasing in height continuous with the cells of
Claudius.

48. A closer look at the organ of Corti

49. Reticular lamina
 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.

50. Deiter’s cells

51. Arrangement of hair cells

52. The spiral ganglion
The cell bodies of the neurons
that form the auditory nerve are
located within the cochlear
modiolus. The collection of cell
bodies is called the spiral
ganglion.

53. Blood supply of labrynth

54. Venous drainage
 Internal auditory vein
 Vein of cochlear aquaduct
 Vein of vestibular aquaduct
Drain into inferior
petrosal and
sigmoid sinuses

55. Internal auditory canal
 About 1 cm long
 Passes into petrous
part of temporal
bone in a lateral
direction
 Lined by dura

58.  At its lateral end (fundus) IAC is
closed by a vertical cribriform
plate of bone that seperates it
from labrynth
 A transverse crest divides this
plate into smaller upper and
larger lower part
 Upper part is again divided into
ant & post part by a vertical
crest called BILL’S BAR.

59. IAC - Contents
 Vestibulocochlear Nerve
 Facial nerve including nervus intermedius
 Internal auditory artery and vein

60. Inner ear fluids
perilymph endolymph
Resembles ECF Resembles ICF
Rich in sodium ions Rich in pottasium ions

62. Endolymph Perilymph CSF
Na+ 5 140 152
K+ 144 10 4
Protien 126 200-400 20-50
Glucose 10-40 85 70

63. THANK YOU