4. AURICLE (PINNA)
Projects at a variable
angle from the side of the
Functions in collecting the
The lateral surface of the
pinna is dominated by
concavities, in particular
5. Triangular fossa.
The scaphoid fossa
Cymba conchae - smaller superior
portion, is the direct lateral relation
to the suprameatal triangle.
Cavum concae-Larger inferior
Lobule– fibrous and
Medial (cranial) surface –
corresponding to the
depressions on the lateral
names, eg. Eminentia
8. Site of endaural incision – will not damage
cartilage or its perichondrium, allows wide
exposure of deeper parts.
Cartilage extends around 8 mm to form lateral
1/3rd of EAC.
Cartilage is covered by perichondrium, from which
it derives its blood supply, cartilage itself is
Cartilage of auricle is connected to the temporal bone
by two extrinsic ligaments.
Anterior ligament – runs from tragus and crus of helix
to the root of zygomatic arch.
Posterior ligament – runs from medial surface of the
concha to the lateral surface of the mastoid prominence.
Intrinsic ligaments connect various parts of the
cartilaginous auricle, between helix and tragus and
another from the antihelix to the posteroinferior portion
of the helix
Extrinsic muscles :- functionally unimportant.
• Anterior auricular muscle
•Superior auricular muscle
•Posterior auricular muscle
Insert into the epicranial aponeurosis.
Temporal and posterior auricular branches of the facial nerve
supply the extrinsic muscles.
11. Intrinsic muscles :- Six in number – are small, inconsistent
and without useful function
12. ARTERIAL SUPPLY
External carotid artery
Posterior auricular artery (dominant artery)
Anterior auricular branches of the superficial temporal
Superior auricular artery
A small auricular branch from the occipital artery
14. NERVE SUPPLY
Both cranial branchial nerves and somatic cervical nerves
supply the auricle. Their distribution is heterogeneous with
Greater auricular nerve ( C2-3 )
Auriculotemporal nerve (branch of V3)
Lesser occipital nerve ( C2 )
Auricular branch of vagus nerve (Arnold nerve)
Facial N. - Probably supplies small region in the root of
17. EXTERNAL AUDITORY CANAL
Approximately 2.4 cm long.
Cartilage in the lateral one-third and bone in the medial two-thirds.
The diameter of the canal varies greatly between individuals and
between different races.
In adults, the cartilaginous portion runs inwards, upwards and
lateral cartilaginous portion is about 8 mm long and is continuous
with the auricular cartilage.
It has two deficiencies – the "fissures of Santorini" in this part of
the cartilage and through them the parotid or superficial mastoid
infections can appear in the canal, or vice versa.
19. The bony canal wall, about 16 mm long, and is narrower than the
Anteroinferior part of the bony canal may present a deficiency
(foramen of Huschke) in children up to the age of four or
sometimes in adults, permitting infections to and from the
The medial end of the bony canal is marked by a groove, the
tympanic sulcus, which is absent superiorly.
The tympanic bone forms the greater part of the canal, and also
carries the tympanic sulcus. The squamous bone forms the roof.
20. There are two suture lines–
the tympanosquamous anteriorly and
There are two constrictions in the canal:
At the junction of the cartilaginous and bony
The isthmus, 5 mm from the tympanic membrane
where a prominence of the anterior canal wall
reduces the diameter.
21. Deep to the isthmus, the anteroinferior portion of
the canal dips forward forming a wedge-shaped
anterior recess between the tympanic membrane
and the canal.
The external canal is lined with skin.
Instead of skin maturation taking place directly
towards the surface, there is outward, oblique
growth of the epidermis of the canal skin and pars
flaccida so that the surface layers effectively
migrate towards the external opening of the canal.
The normal rate of migration is about 0.1 mm/day
22. The absence of hair serves to distinguish the bony and
At the outer limits of the ear canal are some short
hairs that project towards the opening of the canal.
In this region are clusters of ceruminous and
sebaceous glands. The ceruminous glands produce a
watery, white secretion that slowly darkens, turning
semi-solid and sticky as it dries.
The sebaceous glands produce an oily material
(sebum) from the breakdown of their fat-containing
cells which is usually excreted into the root canals of
the hair follicles.
The mixture of desquamated cells, cerumen and sebum
23. Blood Supply
Derived from branches of the external carotid artery.
Auricular branches of the superficial temporal artery
Deep auricular branch of the first part of the maxillary A.
Auricular branches of the posterior auricular artery
The veins drain into
External jugular vein,
The pterygoid plexus
25. NERVE SUPPLY
Auriculotemporal nerve (branch of V3)
Auricular branch of vagus nerve (Arnold nerve)
Facial nerve ( VII )
28. TYMPANIC MEMBRANE
Medial end of the EAC and forms majority of lateral wall of the
Separates EAC from tympanic cavity of middle ear
29. It is slightly oval in shape
Forming an angle of about 55° with the floor.
9-10 mm tall ,8-9 mm wide & thickness 0.1 mm
Most of the circumference is thickened to form a
fibrocartilaginous ring, the tympanic annulus,
which sits in a groove tympanic sulcus.
The sulcus does not extend into the notch of
Rivinus at the roof of the canal, which is formed by
part of the squama of the temporal bone.
30. From the superior limits of the sulcus, the annulus becomes
a fibrous band which runs centrally as anterior & posterior
malleolar folds to the lateral process of the malleus
The handle of malleus is clearly visible within the tympanic
This leaves a small, triangular region of tympanic
membrane above the malleolar folds within the notch of
Rivinus, called the pars flaccida, which does not have a
tympanic annulus at its margins.
The pars tensa forms the rest of the tympanic membrane
32. LAYERS OF TYMPANIC
Outer epithelial layer
Middle, mainly fibrous layer, the
lamina propria; has radially
oriented fibres in the outer layers
and circular, parabolic and
transverse fibres in the deeper layer.
Inner mucosal layer
In the pars flaccida, the lamina
propria is less marked and the
orientation of the collagen fibres
34. ARTERIAL SUPPLY OF THE TYMPANIC MEMBRANE
Arises from branches supplying
both the EAC and the middle ear.
These two sources interconnect
through extensive anastomoses
The epidermal vessels from the
deep auricular branch of the
The mucosal vessels arise from
Anterior tympanic branches of
the Maxillary A.
Stylomastoid branch of the post.
Middle meningeal artery.
35. NERVE SUPPLY
- Auriculotemporal branch
of trigeminal nerve
- Auricular branch of vagus
Tympanic branch of CN IX
( Jacobson’s nerve )
37. THE MIDDLE EAR CLEFT
The middle ear cleft consists of the
Eustachian tube and
mastoid air cell system.
38. THE TYMPANIC CAVITY
Divided into three compartments
the epitympanum (upper)
the mesotympanum (middle)
The epitympanum or attic, lies above the level of the
The mesotympanum lies opposite the tympanic
The hypotympanum lies below the level of the inferior
part of the tympanic sulcus
40. Walls of the Tympanic Cavity
Middle ear is shaped like a narrow box with concave sides
It has 6 walls, which include;
I. Membranous wall (lateral wall)
II. Tegmental wall (roof)
III. Jugular wall (floor)
IV. Carotid wall (anterior wall)
V. Labyrinthine wall (medial wall)
VI. Mastoid wall (posterior wall)
42. THE LATERAL WALL
The lateral wall of the tympanic cavity is formed by the
bony lateral wall of the epitympanum superiorly,
tympanic membrane centrally and
bony lateral wall of the hypotympanum inferiorly.
The lateral epitympanic wall is wedge-shaped in section
and its sharp inferior portion is also called the outer attic
wall or scutum (Latin: 'shield').
It is thin and easily eroded by cholesteatoma, leaving a
telltale sign on a high resolution coronal CT scan.
45. Three holes in the bone of the medial surface of
the lateral wall of the tympanic cavity
The petrotympanic fissure is 2 mm long receives the
anterior malleolar ligament and transmits the anterior
tympanic branch of the maxillary artery to the
The chorda tympani nerve enters through anterior
canaliculus (canal of Huguier)
Posterior canaliculus at the junction of lateral and
46. THE ROOF
The roof of the epitympanum is the tegmen tympani
It is a thin bony plate that separates the middle ear space
from the middle cranial fossa.
It is formed by both the petrous and squamous portions of
the temporal bone .
The petrosquamous suture line, which does not close
until adult life, can provide a route of access for infection
into the extradural space in children.
Veins from the tympanic cavity running to the superior
petrosal sinus pass through this suture line.
47. THE FLOOR
The floor of the tympanic cavity separates the
hypotympanum from the dome of the jugular bulb.
Its thickness varies according to the height of the jugular
Occasionally, the floor is deficient and the jugular bulb is
then covered only by fibrous tissue and a mucous
At the junction of the floor and the medial wall of the
cavity there is a small opening that allows the entry of the
tympanic branch of the glossopharyngeal nerve into
the middle ear.
48. THE ANTERIOR WALL
Narrow as the medial and lateral walls converge.
The lower-third thin plate of bone covering the carotid
This plate is perforated by the
– superior and inferior caroticotympanic nerves
– tympanic branches of the internal carotid artery.
The middle-third-tympanic orifice of the Eustachian tube.
Just above this is a canal containing the tensor tympani
Upper-third is usually pneumatized and may house the
anterior epitympanic sinus, a small niche anterior to the
ossicular heads, which can hide residual cholesteatoma in
canal wall up surgery.
49. THE MEDIAL WALL
Separates the tympanic cavity from the inner ear.
The promontory is a rounded elevation in central
portion of the medial wall.
Covers basal coil of the cochlea and usually has
small grooves on its surface containing the nerves
which form the tympanic plexus.
The promontory gently inclines forwards to merge
with the anterior wall of the tympanic cavity.
51. Behind and above the promontory is the oval window
– kidney shaped opening that connects the tympanic
cavity with the vestibule, which is closed by the
footplate of the stapes and its surrounding annular
Its size 3.25 mm long and 1.75 mm wide.
The oval window niche can be of varying width
depending on the position of the facial nerve
superiorly, and the prominence of the promontory
53. The round window niche lies below and a little
behind the oval window niche from which it is
separated by a posterior extension of the
promontory called the subiculum.
Another ridge of bone, the ponticulus, leaves the
promontory above the subiculum and runs to the
pyramid on the posterior wall of the cavity.
Triangular in shape, with anterior, posterosuperior
and posteroinferior walls.
The latter two meet posteriorly and lead to the
54. The round window membrane
Oval in shape, about 2.3 x 1.9 mm in dimension and
lies in a plane at right angles to the plane of the
Curve towards the scala tympani of the basal coil of
the cochlea, concave when viewed from the middle
Landmark for singular nerve [use full in
neuractomy done for interactable vertigo]
56. The facial nerve canal (or Fallopian canal) runs above the promontory
and oval window in an anteroposterior direction.
It has a smooth rounded lateral surface that often has microdehiscences
When the bone is thin or the nerve exposed by disease, there are two or
three straight blood vessels clearly visible along this line of nerve.
These are the only straight blood vessels in the middle ear and indicate
that the facial nerve is very close by.
The facial nerve canal is marked anteriorly by the processus
cochleariformis, a curved projection of bone, concave anteriorly, which
houses the tendon of the tensor tympani muscle.
Behind the oval window, the facial canal starts to turn inferiorly as it
begins its descent in the posterior wall of the tympanic cavity.
57. THE POSTERIOR WALL
Upper part a large irregular opening - the aditus
Fossa incudis, below the aditus is a small
depression, houses short process of incus & its
Pyramid, a small hollow conical projection with
its apex pointing anteriorly houses the stapedius
muscle and tendon.
59. The facial recess is a groove lies b/w pyramid with facial
nerve, and the annulus of the tympanic membrane .
The facial recess is, therefore, bounded
– medially by the facial nerve and
– laterally by the tympanic annulus,
– with the chorda tympani nerve running obliquely
through the wall between the two.
The chorda always runs medial to the tympanic membrane.
Angle between the facial nerve and the chorda allows a
posterior tympanotomy, allowing access to the middle ear
from the mastoid without disruptiong the tympanic
63. The Sinus tympani
located at the junction of the lateral and posterior
walls of the tympanic cavity.
lies between ponticulus superiorly and subiculum
bounded by pyramidal ridge externally and
64. Posterior extension of the mesotympanum
deep to both the promontory and the facial nerve.
The sinus can extend as far into the mastoid bone
The medial wall ; continuous with the posterior portion of
the medial wall of the tympanic cavity.
where it is related to the oval and round window niches and
the subiculum of the promontory.
Most inaccessible site
66. THE CONTENTS OF THE TYMPANIC CAVITY
The tympanic cavity contains the
– two muscles,
– the chorda tympani and
– the tympanic plexus.
The ossicles malleus, incus and stapes
The Muscles tensor tympani & stapedius
68. THE MALLEUS (the hammer)
Largest, 9 mm in length.
Head, neck and handle or manubrium.
The head lies in the epitympanum
The head of the malleus articulate with the body of
the incus by a synovial joint.
Below the neck lateral process, the anterior
process and the handle.
The lateral process prominent landmark on the
tympanic membrane and receives the anterior and
posterior malleolar folds from the tympanic
69. The chorda tympani crosses the upper part of the
malleus handle on its medial surface above the
insertion of the tendon of tensor tympani, but below
the neck of the malleus itself.
The neck of the malleus connects the handle with
the head and amputation of the head by cutting
through the neck leaves both chorda tympani and
tensor tympani intact.
A slender anterior ligament arises from the
anterior process to insert into the petrotympanic
70. THE INCUS (the anvil)
Articulates with the malleus
Has a body and two processes.
The body lies in the epitympanum and suspended by the
superior incudal ligament
The short process lie in the fossa incudis attached by a
short suspensory ligament.
The long process descends into the mesotympanum and
at its tip is a lentiular process called the fourth ossicle.
Lenticular process articulates with the head of the stapes.
71. THE STAPES (the stirrup)
Shaped like a stirrup
Consists of a head, neck, the anterior and posterior crura
and a footplate.
The head has synovial articulation with the lenticular
process of the incus.
The stapedius tendon inserts into neck and upper portion
of the posterior crus.
The two crura arise from lower part of the neck .
Footplate are 3 mm long-and 1.4 mm wide, and it lies in the
oval window where it is attached to the bony margins by
the annular ligament
72. THE STAPEDIUS MUSCLE
- Arises from wall of conical
cavity within pyramid
- Attaches to neck of stapes
- Helps to dampen loud sound,
preventing noise trauma
- supplied by branch of Facial N
73. TENSOR TYMPANI MUSCLE
● Arises from
a)bony canal above ET
b)cartilagenous part of ET
c) greater wing of sphenoid
● Attaches to neck of malleus
● Tenses tympanic membrane
● Supplied by branch of
74. THE CHORDA TYMPANI NERVE
It enters the tympanic cavity from the posterior
canaliculus at the junction of the lateral and posterior
It runs across the medial surface of the tympanic membrane
between the mucosal and fibrous layers.
Then passes medial to the upper portion of the handle of the
malleus above the tendon of tensor tympani.
Continues forwards and leaves by way of the anterior
canaliculus, which subsequently joins the petrotympanic
75. THE TYMPANIC PLEXUS
– tympanic branch of the glossopharyngeal nerve
– caroticotympanic nerves, arise from the
sympathetic plexus around the internal carotid
The nerves form a plexus on the promontory
Branches -mucous membrane lining the tympanic
cavity, Eustachian tube and mastoid antrum & air cells.
Branches to join the greater superficial petrosal nerve
and the lesser superficial petrosal nerve .
76. THE MUCOSA OF THE TYMPANIC CAVITY
Mucus-secreting respiratory mucosa bearing cilia.
Three distinct mucocilary pathways can be identified
– promontorial and
– hypotympanic, (largest).
Each of these pathways coalesces at the tympanic orifice of
the Eustachian tube.
The mucous membrane lines the bony walls of the tympanic
cavity, and extends to cover the ossicles and their supporting
77. It also covers the tendons of the two middle ear muscles
and carry their blood supply.
These folds separate the middle ear space into
The only route for ventilation of the epitympanic space
from the mesotympanum is via two small openings
between the various mucosal folds - the anterior and
posterior isthmus tympani.
Prussak's space ;between the pars flaccida and the neck
of the malleus, bounded by the lateral malleolar fold
This space can play an important role in the retention of
keratin and subsequent development of cholesteatoma.
94. THE BLOOD SUPPLY OF THE TYMPANIC CAVITY
Arise from both the internal and external carotid system.
The overlap is extensive and great variability is present.
Artery of pterygoid canal and internal carotid arteries.
The anterior tympanic and stylomastoid arteries are
96. THE EUSTACHIAN TUBE
Links the middle ear with the nasopharynx.
Length = 36 mm (reached by the age of 7).
It runs downwards from the middle ear at 45° and is turned
forwards and medially.
The lateral third is bony and arises from the anterior wall of
the tympanic cavity.
Medial two-thirds cartilaginous part.
Its narrowest portion is called the isthmus, where the
diameter is only 0.5 mm or less.
97. It is lined with respiratory mucosa containing goblet cells
and mucous glands, having ciliated epithelium on its floor.
A thin plate of bone forms the roof, separating the tube from
the tensor tympani muscle above.
The carotid canal lies medially and can impinge on the bony
In the nasopharynx, the tube opens 1-1.25 cm behind and
below the posterior end of the interior turbinate.
The opening is triangular in shape and is surrounded above
and behind by the torus.
98. The salpingopharyngeal fold stretches from the lower
part of the torus downwards to the wall of the pharynx.
The levator palati, as it enters the soft palate, results in a
small swelling immediately below the opening of the tube.
Behind the torus is the pharyngeal recess or fossa of
Lymphoid tissue is present around the tubal orifice and in
the fossa of Rosenmuller, and may be prominent in
99. MUSCLES ATTACHED TO THE EUSTACHIAN TUBE
Tensor palati ; arises from the bony wall and the upper
portion of the front wall of the cartilaginous tube.
The muscle converges to a short tendon that turns medially
around the pterygoid hamulus and then spreads out within
the soft palate to meet fibres from the other side in a midline
Separates the tube from the otic ganglion, the mandibular
nerve and its branches, the chorda tympani nerve and the
middle meningeal artery.
It is supplied by the Mandibular Nerve.
100. Salpingopharyngeus is attached to the inferior part of the
cartilage of the tube near its pharyngeal opening, and it
descends to blend with the palatopharyngeus.
Levator palati arises from the lower surface of the
cartilaginous tube and from the lower surface of the petrous
bone, and from fascia forming the upper part of the carotid
It first lies inferior to the tube, then crosses to the medial
side and spreads out into the soft palate.
Salpingopharyngeus and the levator palati are supplied from
the pharyngeal plexus.
101. The ascending pharyngeal and middle meningeal
arteries supply the Eustachian tube.
The veins drain into the pharyngeal plexus and the
lymphatics pass to the retropharyngeal nodes.
The nerve supply arises from the pharyngeal branch of
the sphenopalatine ganglion (Vb) for the ostium,
the nervus spinosus (Vc) for the cartilaginous
portion and from the tympanic plexus (IX) for the
104. There are five recognized regions of pneumatization: the
middle ear, mastoid, perilabyrinthine, petrous apex,
The middle ear :- epitympanic, hypotympanic,
mesotympanic, protympanic & posterior tympanic area
The mastoid region :- mastoid antrum, central mastoid, and
Perilabyrinthine :- supralabyrinthine and infralabyrinthine
Petrous apex region :- The apical area and the peritubal area
Accessory region :- zygomatic, squamous, occipital, and
105. There are five recognized air cell tracts.
The posterosuperior tract runs at the juncture of the
posterior and middle fossa aspects of the temporal bone.
The posteromedial cell tract parallels and runs inferior to
the posterosuperior tract.
The subarcuate tract passes through the arch of the
superior semicircular canal.
The perilabyrinthine tracts run superior and inferior to
the bony labyrinth.
The anterior petrous apex is pneumatized in only 10 to 15%
of specimens. Most often, it is diploic; in a small percentage
of cases, it is sclerotic.
106. The mastoid antrum air-filled sinus in the petrous part of
It communicates with the middle ear by the aditus.
Antrum is well developed at birth.
Volume = 2 ml (adult).
The medial wall relates to the posterior semicircular canal.
More deeply and inferiorly is the dura of the posterior cranial
fossa and the endolymphatic sac.
The roof of the mastoid antrum and mastoid air cell space
form the floor of the middle cranial fossa.
108. SIGMOID SINUS
posterior limit of mastiod cavity.
passes deep part of mastoid process under facial nerve
Angle between middle fossa and posterior fossa dura
plate and superior part of the sigmoid sinus
Laterally in angle with in mastoid cortex –emissarium
mastoidum –bleeding during drilling of corticle bone
109. MacEwen's triangle
– Temporal line
– Posterosuperior segment of bony EAC
– a tangent through the posterior border of EAC
Normally lining of the mastoid is a flattened, nonciliated
epithelium without goblet cells or mucus glands.
111. The inner ear is called as
labyrinth, from the complexity of
It consists of two parts:
1. The osseous labyrinth: A
series of cavities within the
petrous part of the temporal
2. The membranous labyrinth:
A series of communicating
membranous sacs and ducts,
contained within the bony
112. The Osseous Labyrinth (labyrinthus osseous)
Consists of three parts:
canals and cochlea.
These are cavities hollowed
out of the substance of the
bone, and lined by periosteum.
Contain a clear fluid,
perilymph, in which the
membranous labyrinth is
113. The Vestibule (vestibulum)
Central part of the osseous
labyrinth, medial to tympanic
cavity, behind cochlea, and in
front of semicircular canals.
Ovoid in shape, but flattened
About 5 mm. from before
backward, the same from above
downward, and about 3 mm.
In its lateral or tympanic wall is
the fenestra vestibuli, closed by
the base of the stapes and
114. On medial wall, forepart, small circular depression,
the recessus sphaericus, which is perforated, at its anterior
and inferior part, by several minute holes (macula cribrosa
media) for the passage of filaments of the acoustic nerve to the
Behind this depression is an oblique ridge, the crista
vestibuli, the anterior end of which is named the pyramid of the
This ridge bifurcates below to enclose a small depression,
the fossa cochlearis, which is perforated by a number of holes
for the passage of filaments of the acoustic nerve which supply
the vestibular end of the ductus cochlearis.
116. Hinder part of the medial wall is the orifice of the aqueductus
vestibuli, which extends to the posterior surface of the petrous
portion of the temporal bone.
On the upper wall or roof is a transversely oval depression,
the recessus ellipticus, separated from the recessus sphaericus
by the crista vestibuli.
The pyramid and adjoining part of the recessus ellipticus are
perforated by a number of holes (macula cribrosa superior).
The apertures in the pyramid transmit the nerves to the utricle.
117. The Bony Semicircular Canals
3 in number
superior, posterior, and lateral,
Above and behind the vestibule.
Unequal in length
Each measures about 0.8 mm. in
diameter, and presents a dilatation
at one end, called the ampulla
They open into the vestibule by five
orifices, one of the apertures being
common to two of the canals
118. The superior semicircular canal
15 to 20 mm. in length.
vertical in direction, and
placed transversely to long
axis of petrous portion of
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
119. The posterior semicircular canal
Vertical, is directed backward,
nearly parallel to the
posterior surface of the
Longest 18 to 22 mm.
It’s lower or ampullated end
opens into the lower and back
part of the vestibule, its upper
into the crus commune.
120. The lateral or horizontal canal
12 to 15 mm.
Its ampullated end corresponds
to the upper and lateral angle of
the vestibule, just above the
It’s opposite end opens at the
upper and back part of the
121. THE COCHLEA
Resemblance to a common snail-shell
Anterior part of the labyrinth.
It is conical in form, and placed almost horizontally in front of the vestibule.
Apex (cupula) is directed forwards and lateral toward the upper and front part
of the labyrinthic wall of the tympanic cavity.
Base bottom of the internal acoustic meatus, and is perforated by numerous
apertures for the passage of the cochlear division of the acoustic nerve. It
measures about 5 mm. from base to apex, and its breadt is about 9 mm
122. The modiolus
Conical central axis of the cochlea.
Base is broad at the bottom of the
Perforated by numerous orifices,
transmit filaments of the cochlear
division of acoustic nerve.
The nerves for the first turn and a
half, pass through the foramina of
the tractus spiralis foraminosus.
Those for the apical turn,pass
through the foramen centrale.
123. The bony canal of the cochlea
takes two turns and three-
quarters around the modiolus.
It is about 30 mm. in length,
and diminishes gradually in
diameter from the base to the
summit, where it terminates in
The beginning of this canal is
about 3 mm. in diameter
124. 1st the fenestra
cochlea, communicates with the
tympanic cavity closed by
the secondary tympanic
2nd of an elliptical form, opens into
3rd is the aperture of the
aquaeductus cochleae, opens on
the inferior surface of the petrous
part of the temporal bone and
forms a communication between
the subarachnoid cavity and the
125. The osseous spiral lamina
Bony shelf projects from
modiolus into interior of canal,
like canal takes two and three-
quarter turns around
It reaches about half-way
toward the outer wall of the
tube, and partially divides its
cavity into two passages or
scalae, upper scala vestibuli,
lower scala tympani.
the two scalae communicate
with each other.
126. The osseous labyrinth is lined
by an exceedingly thin fibro-
It’s attached surface is rough
and fibrous, and closely
adherent to the bone.
It’s free surface is smooth and
pale, covered with a layer of
epithelium, and secretes a thin,
limpid fluid, the perilymph.
127. The Membranous Labyrinth
The membranous labyrinth is
lodged within the bony cavity,
separated from the bony walls by a
quantity of fluid, perilymph.
In certain places it is fixed to the
walls of the cavity.
The membranous labyrinth
contains fluid, the endolymph, and
on it’s walls the ramifications of
the acoustic nerve are
Rich in Na+ ions.
1)filtrate of blood serum
from capillaries of spiral
2)CSF reaching labyrinth
via aqueduct of cochlea.
Rich in K+ ions.
1) Stria vascularis
2) Dark cells of utricle &
ampullated ends of
131. Cochlear duct
Also called membranous cochlea/scala
Blind coiled tube
Triangular on cross section
3 walls are formed by
Basilar membrane which support organ
Reissner membrane which separates it
from scala vestibuli
Stria vascularis – secretion of
Cochlear duct connected to saccule by
132. The stria vascularis is composed of 3 cell types:
1.Marginal cells, which line the endolymphatic
canal and have an essential role in ion exchange
2. Intermediate cells, which are rich in the
3. Basal cells.
133. THE UTRICLE
Larger of the two, is of an oblong
form, and occupies the upper and
back part of vestibule.
The portion which is lodged in the
recess forms a sort of pouch or cul-
de-sac, the floor and anterior wall of
which are thickened, and form
the macula, which receives the
utricular filaments of the acoustic
The cavity of it communicates with
the semicircular ducts orifices.
134. The Saccule
Globular in form and lies in the recessus sphaericus.
Its anterior part exhibits an oval thickening, macula, to which
are distributed the saccular filaments of the acoustic nerve.
Its cavity does not directly communicate with that of the
Posterior wall a canal, the ductus endolymphaticus, is given off;
this duct is joined by the ductus utriculosaccularis, and then
passes along the aquaeductus vestibuli and ends in a blind
pouch (saccus endolymphaticus) on the posterior surface of the
petrous portion of the temporal bone, where it is in contact with
the dura mater
From the lower part of the saccule a short tube, the canalis
reuniens of Hensen, passes downward and opens into the
ductus cochlearis near its vestibular extremity9/29/2015 134
135. SEMICIRCULAR DUCTS
3 in no.
Correspond exactly to bony canals
Open in utricle
Ampullated end of each duct contains neuroepithelium
called crista ampullaris.
136. The walls of the utricle, saccule, and semicircular ducts consist of
The outer layer is a loose composed of ordinary fibrous tissue
containing blood vessels and some pigment-cells.
The middle layer, thicker more transparent, forms a
homogeneous membrana propria, and presents on its internal
surface, especially in the semicircular ducts, numerous
The inner layer is formed of polygonal nucleated epithelial cells.
In the maculae of the utricle and saccule, and in the transverse
septa of the ampullae of the semicircular ducts, the middle coat is
thickened and the epithelium is columnar, and consists
of supporting cells and hair cells.
137. There are two types of hair
cells in the semicircular
canals and the vestibule.
Type I hair cells are flask-
shaped cells while type II hair
cells are cylinder-shaped cells.
Type I and type II hair cells
are very similar in their
structure and innervation to
the inner hair cells and the
outer hair cells of the organ of
138. The organ of Corti converts the mechanical vibrations into
The fibers of the auditory nerves travel from the organ of Corti
through a system of small perforations in the spiral lamina
collectively called habenula perforata.
From habenula perforata, nerve fibers travel through a channel
in the center of the modiolus (Rosenthal's canal), exit the base
of the cochlea, and join vestibular nerve fibers to form the
139. There are two types of hair cells in the organ of
Corti: the inner hair cells (IHCs) and the outer
hair cells (OHCs).
• The groups of IHCs and OHCs are separated by
two rods (pillars) of Corti, which structurally
support the organ of Corti.
140. The rods are attached at their
tips and more widely
separated at the base,
forming a triangular shape
called the tunnel of Corti.
The tunnel is filled with the
cortilymph fluid that has
similar properties to the
perilymph fluid found in the
141. The tops of the hair cells and
supporting cells of the organ
of Corti are tightly connected
together at their tips to form a
continuous layer called the
The reticular lamina isolates
all of the organ of Corti from
the endolymph of the scala
media except for stereocilia
which project through the
reticular lamina into the
142. The OHCs are held in position
by the outer rod of Corti on one
side and by Deiters cells on
the other side.
Each Deiters cell holds an
OHC at the bottom and
through long projections called
phalangeal processes from
The middle part of an OHC is
not firmly supported and is
surrounded by a perilymph-
filled space called the space of
143. Next to the Deiters cells,
towards outer end of cochlea,
there are several groups of
supporting cells, called Hensen
cells, Claudius cells, outer spiral
sulcus cells, and Boettcher cells.
Lateral to these support cells is
Stria vascularis, highly vascular
organ attached to the outer
surface of the scala media.
Stria vascularis recycles K+ and
produces endolymph for scala
media, thus maintaining
endocochlear potential of inner
144. ENDOLYMPHATIC DUCT & SAC
Duct formed by union of 2
ducts each from utricle &
Passes through vestibular
Terminal part dilated to
form sac lies b/w 2 layers
of dura posterior surface
of tympanic bone
145. Nerve supply
The vestibular nerve supplies utricle, saccule and ampullae of
the semicircular ducts.
On the trunk of the nerve, within the IAM, is a ganglion,
the vestibular ganglion (ganglion of Scarpa); the fibers of the
nerve arise from the cells of this ganglion.
On distal side of ganglion nerve splits into a superior, an
inferior and a posterior branch.
The filaments of the superior branchmacula of the utricle and
in the ampullae of the superior and lateral semicircular ducts
inferior branchmacula of the saccule.
The posterior branch runs through the foramen singulare at the
postero-inferior part of the bottom of the meatus and divides
into filaments for the supply of the ampulla of the posterior
semicircular duct.9/29/2015 145