5. Bony labyrinth
Vestibule – central chamber of labyrinth. In its lateral wall
lies the oval window. Inside of its medial wall present two
recess, a spherical recess lodges the saccule and an
elliptical recess which lodges the utricle.
Semicircular canals -The vestibule and semicircular
canals are concerned with vestibular function (balance)
Cochlea- The cochlea is concerned with hearing.
8. Parts of the Membraneous labrynth
Cochlear duct
Utricle
Saccule
Three semicircular canals
Endolymphatic duct and sac
9. Membranous labyrinth
Within the cavity is the membranous labyrinth,
with 2 sacs:
A. Utricle
B. Saccule
C. 3 semicircular ducts from the utricle(
anterior, Posterior, lateral)
D. cochlear duct (bony spiral)
Endolymph, fluid within the membranous
labyrinth
Perilymphatic space, separates the osseous
from the membranous labyrinth
Perilymph, fluid within the perilymphatic space.
11. Semicircular Canals
Three semicircular canals-
Lateral (Horizontal)
Superior ( Anterior vertical)
Posterior ( Posterior vertical)
Each canal is 0.8 mm in diameter, has a ampullated
limb measuring 2mm in diameter & a nonampullated
limb which is 1mm in diameter.
Occupies 2/3rd of a circle
Ampulla is cribrosed for passage of nerve fibers
Ampullated & nonampullated limbs all open into the
vestibule
The non ampullated ends of posterior and superior
canals join & form Crus Commune (4 mm length) it
opens into medial part of vestibule.
So three SCC opens into vestibule by 5 openings.
14. Trautmann’s triangle.
The triangle bounded by the bony labyrinth, sigmoid
sinus, and superior petrosal sinus is known as
Trautmann’s triangle.
15. This triangle is a potential weak spot through which
infections of temporal bone may traverse and
affect cerebellum.
Extra dural abscess involving the posterior cranial
fossa is also possible when thin bone in this triangle
gets breached in infections / cholesteatoma involving
mastoid cavity.
Since bone in this area is rather thin it can be drilled
out to enter into the posterior cranial fossa. This can
be used as an approach to posterior cranial fossa
lesions.
The size of this triangle is highly variable depending
on the size of the sigmoid sinus. A large sigmoid sinus
reduces the size of this triangle and also increases
the angulation of the superior petrosal sinus with it.
This impedes the venous drainage predisposing to
the development of endolymphatic hydrops.
16. Horizontal semicircular canal
The lateral or horizontal canal (external semicircular canal) is the
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).
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.
Its ampullated end corresponds to the upper and lateral angle of
the vestibule, just above the fenestra vestibuli, where it opens
close to the ampullated end of the superior canal; its opposite
end opens at the upper and back part of the vestibule.
The lateral canal of one ear is very nearly in the same plane as
that of the other; while the superior canal of one ear is nearly
parallel to the posterior canal of the other.
17. Superior semicircular canal
The superior semicircular canal (anterior semicircular
canal) detects rotation of the head around a rostral-
caudal (anterior-posterior) axis, or in other words
rotation in the coronal plane. This occurs, for
example, when you move your head to touch your
shoulders.
It is 15 to 20 mm in length, is vertical in direction, and
is placed transversely to the long axis of the petrous
portion of the temporal bone, on the anterior surface
of which its arch forms a round projection.
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.
18. 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.
It is directed superiorly, as per its nomenclature, and
posteriorly, nearly parallel to the posterior surface of
the petrous bone.
The vestibular canaliculus is immediately medial it.
It detects rotations of the head in the sagittal plane. It
is the longest of the three canals, measuring from 18
to 22 mm. Its lower or ampullated end opens into the
lower & back part of the vestibule, and upper end into
the crus commune.
19.
20. Semicircular Canals
Each membranous semicircular canal is filled with
endolymph, a potassium-rich extracellular fluid, and
is bathed in perilymph, which has the approximate
composition of cerebrospinal fluid.
Ampulla, which contains the crista ampullaris and
cupula. The crista ampullaris is a saddle-shaped
gelatinous structure along one wall of the
membranous canal that contains hair cells, the
sensory cells of the vestibular system.
The cupula acts as a membranous diaphragm,
stretching from the crista to the opposite walls of the
canal.
• Crista and cupula in each ampulla sense angular
acceleration
21. The attachment of the cupula, which extends from the apex of the
crista to the opposite wall of the membranous ampulla. Arrowheads
indicate subcupular space.
22. Vestibule
Central chamber of labrynth (5 mm)
Lateral wall contains oval
window(fenestra vestibuli) – closed
by footplate of stapes sorrounded
by annular ligament.
23. Otolithorgans
The utricle and saccule, together called the otolithorgans,
also contain hair cells that bend in response to
acceleration of the head.
Instead of cristae, however, the sensory epithelium of
these organs is covered by flat, kidney-shaped sheets
called maculae.
24. One macula is applied horizontally to the ceiling of the
utricle, whereas the other hangs sagittally on the wall of
the saccule. Each macula is a gelatinous matrix into
which hair cells project and which is studded with tiny
calcium carbonate granules called otoconia.
25. Whereas the cristae have a specific gravity identical to
the surrounding endolymph, the otoconia increase the
density of the maculae and render them sensitive to
shearing forces parallel to their surfaces caused by
gravity or linear motions of the head.
Any time the head moves linearly, the heavy maculae lag
behind, bending the hair cells embedded in them. The
utricle primarily senses lateral tilt and translation of the
head, whereas the saccule measures front-to-back tilt
and translation as well as motion aligned with the pull of
gravity.
26. Hair cells located in the sensory
epithelia of the semicircular
canals and otolith organs are
responsible for transforming
motion into a modulation in the
discharge rate of afferent nerve
fibers innervating the vestibular
nerve.
27. Utricle
Walls are composed of:
a. outer fibrous layer
b. intermediate delicate vascular connective tissue
c. inner squamous to low cuboidal except in
specialized receptor regions that are columnar and
more complex.
28. Saccule
Endolymphatic duct = small ducts from utricle & saccule, Lined
by squamous to cuboidal epithelium up to membranous
labyrinth, near end it is transitional to tall columnar cells.
Endolymphatic sac is active site for absorption of endolymph.
Dark cells
Large irregular shaped nucleus,
smooth free surface.
Cell base has shallow
infoldings of the membrane.
Light cells free surface has
profuse long microvilli,
numerous micropinocytotic
invagination of membrane.
With clear vacoules in apical
cytoplasm
Plasma membrane at cell base
is smooth
Lateral membrane is
extensively interdigitate with
neighboring cells.
Specialized for absorption.
29. utricle
Oblong and irregular
Has anteriorly upward slope at an apparent
angle of 30
It lies in posterior part of bony vestibule &
recieves the five openings of three SCC
Utricle(4.33 mm) is bigger than saccule (2.4
mm) & lies superior to saccule
Utricle connected to saccule via
utriculosaccular duct
Its sensory organ macula is concerned with
30. Utricle ……
Dark and light cells are distinguishable in unspecialized regions
of the epithelium.
Dark cells have highly
irregular nuclei outline,
located near the apical
surface
apical cytoplasm contains
coated vesicles, larger
smooth vesicles,
occasional lipid droplets.
Basal cytoplasm with long
mitochondria.
Function =Responsible for
ionic composition of the
endolymph.
Light cells have sparse
microvilli on apical
surface, occasional
micropinocytosis vesicles.
Cytoplasm has small
numbers of ribosomes &
few mitochondria.
Function = Ion
transporting cells.
31. Macula Utriculae…
Found in the floor of the utricle, a thick special sensory epithelium,with
hair cells & supporting cells.
The kinocilium & stereocilia of the hair cells project into the underside
of the Otolithic membrane
Otoliths (otoconia) = minute 3-5um crystalline bodies of protein &
calcium carbonate embedded in Otolithic membrane.
32. Endolymphatic duct and sac
Ducts from utricle and saccule unites and form
utriculosaccular duct
Continues as endolymphatic duct that passes
via the vestibular aqueduct
33. saccule
lies anterior to utricle opposite the stapes footplate in
the bony vestibule.
its sensory organ macula is concerned with linear
acceleration & decelaration.
Saccule is connected to the cochlea via a thin reunion
duct.
34. Saccule
Macula of saccule - ovoid thickening of the
wall of the anterior globular saccule.
Found in the vertical anterior wall, hair cells
responds to movements at right angle &
activate the macula of utricle which is in
horizontal position when head is in upright
position, providing info to brain regarding
head position as to pull of gravity.
Ductus utriculosaccularis - communication
between utricle to saccule.
Ductus reuniens - short tube that runs from
the saccule to basal end of cochlear duct.
35. Saccule
Endolymphatic duct - small ducts from utricle & saccule, Lined
by squamous to cuboidal epithelium up to membranous
labyrinth, near end it is transitional to tall columnar cells.
Endolymphatic sac is active site for absorption of endolymph.
Dark cells
Large irregular shaped nucleus,
smooth free surface.
Cell base has shallow
infoldings of the membrane.
Light cells free surface has
profuse long microvilli,
numerous micropinocytotic
invagination of membrane.
With clear vacoules in apical
cytoplasm
Plasma membrane at cell base
is smooth
Lateral membrane is
extensively interdigitate with
neighboring cells.
Specialized for absorption.
37. The 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.
38. Modiolus ?
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
39. Spiral lamina = spiral ledge from modiolus to
cochlear canal.
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 is a critical step in the transduction
process.
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.
Lumen of cochlear canal is partitioned into 3 spiral
chambers:
1. scala vestibuli (above)
2. scala tympani (below)
40.
41. Osseous spiral lamina ?
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.
1. Scala vestibuli
2. Scala tympani
3. Scala media (membraneous cochlea)
42.
43. Rosenthal’s canal ?
Spiral ganglions are situated in this canal
which runs along the osseous spiral
lamina.
44. The cochlea uncoiled
Movement of the the basilar membrane by
pressure changes induced by stapes footplate
motion at the oval window is a critical step in the
transduction process
45. Scala vestibuli ?
This uppermost channel is continuous with
vestibule and closed at oval window by
stapes footplate
46. Scala tympani ?
This lowermost channel is closed by
secondary TM of round window
47. Scala media ?
Bind coiled tube, connected to the saccule
via ductus reunions.
48. Aqueduct of cochlea?
A bony bulge in the medial wall of middle
ear , represents the basal coil of cochlea.
Promontory ?
Scala tympani is connected with
subarachnoid space via aqueduct of
cochlea.
It is thought to regulate perilymph &
pressure in bony labrynth.
50. Cochlear duct-relations &
boundaries
1. Basilar membrane – base
It supports organ of corti
2. Reissners membrane
Seperates scala media from scala vestibuli
3. Stria vascularis
It contains vascular epithelium and secretes
endolymph
51. Scala media is more or less triangular, formed by
Reissner’s membrane, basilar membrane and the
structure called the stria vascularis.
The fluid that fills scala tympani and scala
vestibuli is called perilymph; the fluid that fills
scala media is called endolymph.
The organ of Corti rests on the basilar membrane
within scala media.
52. Spiral limbus
Limbus = A bulging of the osseous spiral lamina into
the scala media.
The inner angle convergence of the vestibular
membrane and basilar membrane.
Internal spinal sulcus = a tapering upper edge
projecting laterally over the recess of internal spinal
sulcus( tunnel).
Auditory teeth = vertically oriented collagen fiber
bundles within the limbus.
Interdental teeth = uniformly spaced along the upper
surface of the limbus between auditory teeth, secretes
the Tectorial membrane.
53. 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 mucopolysaccharides.
Fibers consists of a protein similar to epidermal
keratin.
54. Basilar membrane
Extends across the cochlear canal from spiral lamina to
the spiral ligament.
Separates the scala media from the scala tympani
Supports the Organ of Corti
0.25 mm across x 35 m long from base of cochlea to apex.
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, with radially oriented 10 nm collagen like
fibrils.
Zona pectinata= thicker from organ of Corti to spiral
ligament. Trilaminar in structure. Upper layer is meshwork
of transverse fibers. Lower layer is of longitudinal fibers.
In between is structureless intermediate layer of few
fibroblasts like cells.
* The width of fibers vary from 0.20 mm to 0.36 mm at the
apex, the diameter of component fibers gradually
decreases vibrate at higher frequency near base and
lower frequency near the Helicotrema, thereby
55.
56. Notice the stria vascularis
(also area vascularis) –
The s.v. secretes
endolymph.
Notice also the spiral
ligament, which
attaches the b.m. to
the bony wall of the
cochlea, and the
limbus (or limbus
spiralis), a fibrous
covering of the spiral
lamina.
modiolus spiral ligament
58. Inner ear fluids
perilymph – between bony and membraneous labrynth
Endolymph fills the entire membraneous labrynth
perilymph endolymph
Resembles ECF Resembles ICF
Rich in sodium ions Rich in pottasium ions
59.
60. The terminal part of the endolymphatic duct is dilated and
forms endolymphatic sac , which is situated between two
layers of dura on the posterior surface of petrous bone.
61. Organ Of Corti
The end organ of hearing
Inner pillar cells - broad base, resting on the basilar membrane,
slender and conical, nucleus is basal.
Inner tunnel - wide triangular intercellular space continuous thru
cochlear length. Bounded above converging inner and outer pillar
cells,
Outer pillar cells -longer and more oblique, leaning to the inner
pillars.with broad thin base.
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.
62. 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.
2 types of hair cells in cochlea:
A. inner hair cells - like type 1 hair cells, single row along the entire
length of the cochlea.
B. Outer hair cells - 3 rows between pillar cells and outer phalangeal
cells
63. Two types of cells in the organ of Corti are support cells
and hair cells.
The hair cells are the “receptor” cells-- the ones that
transduce sound.
Support cells such as the Deiter’s cells support hair cells.
The tops of the hair cells and pillar cells form the reticular
lamina, which isolates the hair cells’ stereocilia from their
cell bodies. The tectorial membrane is loosely coupled to
the reticular lamina.
There are 4 rows of hair cells,
One row on the inner (modiolar) side of the tunnel formed by
the pillar cells-- these are the inner hair cells
3 row on the outer side of the Tunnel of Corti, these are the
outer hair cells.
Deiter’s cells support the Outer hair cells at their base, but
71. Cochlea
The cochlea contains an array of highly
specialized cells arranged in a highly specialized
manner.
There are structural differences between IHCs
and OHCs that suggest that they differ in function
The cochlea not only sends a message to the
brain, but it may also receive messages from the
brain via efferent innervation.
73. 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.
74. Pattern of afferent innervation
•Different types of
nerve fibers
innervate IHCs and
OHCs.
•Type I fibers
innervate IHCs
• Type II neurons
innervate OHCs.
75. Pattern of afferent innervation
•Nearly all of the nerve fibers
that carry messages from the
ear to the brain innervate inner
hair cells.
• Each IHC has its own “private”
set of fibers.
•The Type II nerve fibers
innervate many OHCs. and the
OHCs they innervate are basal
to the point at which the nerve
fiber enters the cochlea.
77. Pattern of efferent innervation
Neurons from the brainstem also contact hair
cells.
These neurons carry information from the brain to
the ear and are called efferent neurons.
The vast majority of efferents 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.
81. Venous drainage
Internal auditory vein
Vein of cochlear aquaduct
Vein of vestibular aquaduct
Drain into inferior
petrosal and
sigmoid sinuses
82. Internal auditory canal
About 1 cm long
Passes into petrous part of temporal bone in a lateral
direction
Lined by dura
83. Internal auditory canal
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.
84. IAC - Contents
Vestibulocochlear Nerve
Facial nerve including nervus intermedius
Internal auditory artery and vein
85. Development of inner ear
Initially membraneous labrynth , followed by
encasement by bony labrynth.
Starts within first few days( 22- 23 days)
Ectodermal thickening in hind brain
Otic placode
Otic pit
Oticyst
Membraneous labrynth
(by 25 th week of GA)
87. Development of inner ear
BONY LABRYNTH
Mesenchyme enclosing the otocyst becomes
chondrified to form otic capsule
Ossification begins in around 16 th week
Certain channels remain within otic capsule like
oval window where part of the otic capsule becomes
the stapes footplate and the annular ligament.
93. Mondini Aplasia
AD
Most common cochlear abnormality
Progressive or fluctuating HL
risk of perilymphatic gusher and meningitis
from dilated cochlear aqueduct
Dx: CT reveals single turned cochlea, no
interscalar septum
Tx: HA, cochlear implant
96. Noise Damage
Temporary Threshold Shift (TTS)
Permanent Threshold Shift (PTS)
Duration, Timing and Intensity influence
Typical “Noise Notch” often seen between
____________ first.
Notch widens and deepens over time, with
hearing loss spreading to adjacent frequencies,
and increasing in degree.
98. 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.
Each kinocilium is limited by
plasma membrane & with
several bundles of Actin
filaments spaced 10 nm apart &
crosslinked by Fimbrin minute
proteins.
Nerves penetrate between
Supporting cells.
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.
The base do not form a calyx
but end in small terminal
boutons.
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.
Others end as dense
(granulated vesicles) carry
efferent nerve impulses
modulating the sensitivity of
100. Perilymphatic labyrinth
The space surrounding the membranous labyrinth.
Includes the narrow space between the utricle and
saccule.
Contains cells, fibers and perilymph fluid rich in K+ and
low in Na+.
Nerves of the Labyrinth.= Vestibular and Cochlear
nerves.
Internal auditory meatus of the Temporal bone = where
Cell bodies of the afferent fibers are bipolar cells found in
the spiral ganglion (Cochlear ganglion) in the Modiolus
and Vestibular ganglion
( Scarpa’s ganglion).
102. Blood vessels = labyrinthine artery from the inferior cerebellar artery
vestibular artery common cochlear artery vestibulochlear
artery ( utricle / saccule) cochlear artery proper spiral
modiolar artery.
Venous drainage
A. spiral prominence to periostium of scala tympani to spiral
vein.
B. small vein of spiral lamina to plexus in modiolus into the
internal auditory vein or cochlear aqueduct to jugular veins.
C. vestibular veins into vestibular and cochlear aqueducts.
True lymphatics is absent in the labyrinth. Fluid drain into
perilymphatic space to subarachnoid space, to the perivascular
and perineural connective tissue sheath
