Anatomy Of The Ear

Prof. Dr. Mohamed Talaat EL.Ghonemy

ANATOMY OF EXTERNAL EAR
 1- AURICLE

 2- External
Auditory Canal

 3- Tympanic
 membrane
The auricle

Is a framework of a single piece

of yellow elastic cartilage
covered with skin which is
closely adherent to the
perichondrium except ; The
lobule .
 The external auditory canal
* LENGTH = 24 mm.
1- Cartilagenous portion ;
* Outer 1/ 3 = 8 mm: Directed
upwards & backwards .
Skin is thick , contains
hair& ceruminous glands.
2 – Bony portion ;
* Inner 2 / 3 = 16 mm:
Directed downwards &
forwards . Skin is thin
,sensetive,hairless &
closely adherent to bone.
Functions Of The External Auditory Canal
1- Conduction of sound waves .
2- Amplification of sound .
3- Protection of the middle & inner ear :
- The Angle between bony & cartilagenous parts.
- Highly sensitive skin of the inner part .
- Hair of the outer part .
- Wax : --Has a bactericidal activities .
-- Filtrates fine particles of dust & pollens .
•Relations of the external auditory canal ;
# Anteriorly : T.M.J
# Posteriorly : Mastoid air cells
# Superiorly : Middle cranial fossa
# Inferiorly : Parotid gland
Tympanic membrane (drum)

 It is an oval, concave,
glistening, mobile membrane
and is approximately 8 -10 mm
in diameter.
 The tympanic membrane is
divided into two parts:
(a) Pars Tensa
 Most of the tympanic membrane

 fibrous annulus.

 Handle of malleus: umbo.

 A bright cone of light

(b) Pars Flaccida (Shrapnel's

Membrane)
 Above the anterior and posterior
malleal folds.
 The middle fibrous layer of the
pars flaccida is weaker than that
of the pars tensa with an
incomplete annulus.
Layers of the tympanic membrane:
Three layers:

(i) Outer epithelial layer, which is

continuous with the skin lining the
external meatus.

(ii) Inner mucosal layer, which is

continuous with the mucosa of the
middle ear.

(iii) Middle fibrous layer, which

encloses the handle of malleus.
The Middle Ear Cleft ;
It Consists Of ;
1- The Tympanic Cavity .
2- The Eustachian Tube.
3- The Mastoid Air Cells .
The Tympanic Cavity ; 6 side box
1- Roof ; Tegmen tympani
A thin plate of bone separates
tympanic cavity from the middle
cranial fossa .

2- Floor ;
- A thin plate of bone separates
it from the jugular bulb .
- It may be congenitally dehiscent .
3- Anterior Wall ;
- Canal for chorda tympani nerve.
- Canal for tensor tympani muscle.
- Eustachian Tube .
- Carotid artery.

4- Posterior Wall ;
- Aditus ad antrum .
- Bony pyramid ( stapeduis)
- Vertical part of facial nerve
5- Medial Wall ;

a- The promontory
( basal turn of cochlea)
b- Round window
(secondary TM).
c- Oval window
( stapes footplate).
d- Tympanic part of facial
nerve .
6- Lateral Wall ;

a- Tympanic membrane .
b- Outer attic wall (above).
c- Hypotympanium (below).
Relations of the middle ear cleft:

 Laterally, the tympanic

membrane.
 -Medially, the inner ear.
 -Superiorly, the middle cranial
fossa.
 -Inferiorly, the jugular bulb.
 -Anteriorly, Eustachian tube.
 -Posteriorly, the mastoid
antrum and cells by the aditus
and antrum.
Contents Of The Middle Ear ;

-- 3 Ossicles.
-- 2 Muscles.
-- 2 Nerves.
3 Ossicles
Yellow: malleus
Green : incus
Red : stapes
Malleus
Incus
Stapes
1.Malleus. 2.Malleus ligament. 3.Incus .4.Incus ligament.
5.Stapedius muscle. 6.Stapes footplate. 7.Drum.
8.Eustachian tube. 9.Tensor tympani. 10.Chorda tympani.
 Two muscles:
 -Tensor tympani muscle arises from
a tunnel above the osseous part of
Eustachian tube and is inserted into
the neck of malleus. It tenses the
tympanic membrane. It is supplied
by a branch of the mandibular
nerve.
 -Stapedius muscle arises from the
pyramid and is inserted into the
neck of stapes. It helps to dampen
very loud sounds thus preventing
noise trauma to the inner ear. It is
supplied by a branch from the facial
nerve.
 Two nerves:
-The chorda tympani nerve is a branch
of the vertical part of the facial nerve.
It runs on the medial surface of the
tympanic membrane between the
handle of malleus and long process of
incus. It carries taste from the anterior
two thirds of tongue and supplies
secretomotor fibres to the
submaxillary and sublingual salivary
glands.

-The tympanic plexus lies on the

promontory under the mucosa and is
formed by (i) tympanic branch of
glossopharyngeal nerve and (ii)
sympathetic fibres from the plexus
round the internal carotid artery. It
contains sensory fibers to the
tympanic cavity and the drum.
 The middle ear is divided into
mesotympanum opposite the
drum, attic (epitympanum) above
the drum and hypotympanum
below the drum.
The Eustachian Tube
3.6 cm in length - Its lateral 1/3 is bony & lower2/3 is cartilagenous
It is closed at rest & opens by the action of tensor palati muscle
during swallowing and yawning to equalize air pressure on both
sides of the T.M.
Wider, shorter & more horizontal in children (Rec O M).
 Mastoid antrum and cells

3 types of mastoid bone have been

described; (i) Well-pneumatised or
cellular. (ii) Diploetic. (iii) Sclerotic or
acellular

-- Mastoid Antrum.
-- Subdural.
-- Sinu-dural.
-- Peri-sinus.
-- Peri-facial.
-- Peri-labyrinthine.
-- Zygomatic.
-- Tip cells.
Anatomy of the inner ear ;
* It lies in the petrous part of the temporal bone .
* Called the labyrinth .
* It consists of the bony & the membranous labyrinth .
The Bony labyrinth ;
1- The bony cochlea anteriorly .
2- The vestibule posteriorly .
3- The bony semicircular canals ( 3 ) .

* It contains perilymph in which the

Memberanous labyrinth is situated .
Bony Labyrinth
It consists of three parts: the vestibule,
the 3 semicircular canals and the cochlea.
1. Vestibule is the central
chamber of the labyrinth. In
its lateral wall lies the oval
window. The inside of its
medial wall presents two
recesses for the saccule
and the utricle. In the
posterosuperior part of the
vestibule are the five
openings of semicircular
canals.
 2. Semicircular canals are
three in number: the
lateral, posterior and
superior, which lie in
planes at right angles to
one another. The three
canals open into the
vestibule by five openings
(the superior and the
posterior canals open into
a common opening).
3. Bony cochlea is a coiled tube making
2.5 turns. The bony cochlea contains
three compartments:
(a) Scala vestibuli, above and is closed
by the footplate of stapes.
(b) Scala tympani, below and is closed
by secondary tympanic membrane
(c) Scala media or the cochlear duct.
The membraneous labyrinth , consists of ;
the cochlear duct, the utricle and saccule, the
three semicircular ducts, and the endolymphatic
duct and sac.
N.B. it contains endolymph =similar to intracellular
fluid =high k - low Na .
1. Cochlear duct (scala media):
-The organ of corti lies on the basilar
membrane. It is the neuroepithilium
of hearing
-3 rows of outer hair cells at the basal
coil & one row of inner hair cells at
the apical coil.
-higher frequencies of sound are heard
at the basal coil while lower ones are
heard at the apical coil.
-The cochlear duct is separated by the
scala vestibuli from above with the
Reissner' membrane and by the
scala tympani with the basilar
membrane from below.
-The cochlear duct contains the stria
 2. Utricle and saccule:

 The utricle lies in the posterior part

of bony vestibule. It receives the five
openings of the three semicircular
ducts. The saccule anterior to the
utricle and opposite the stapes
footplate. The sensory epithelium of
the utricle and saccule is called the
macula and is concerned with linear
acceleration and deceleration.
 3. Semicircular ducts:

 They are three in number and

correspond exactly to the three bony
canals. They open in the utricle. The
ampulated end of each duct
contains the sensory epithelium
called crista ampullaris which is
concerned with angular
acceleration.
 4. Endolymphatic duct and sac:

 Endolymphatic duct is formed

by the union of two ducts from
the saccule and the utricle. Its
terminal part is dilated to form
endolymphatic sac which lies
between the two layers of the
dura on the posterior surface of
the petrous bone.
 Nerve supply of the ear
-Sensory
Auricle:
Medial aspect: lesser
occipital C 2 and great
auricular C 2&3.
Lateral aspect: great
auricular C2&3 and
auriculotemporal of
trigemenal nerve.
External auditory canal:
Anteriorly: auriculotemporal of trigemenal nerve.
Posteriorly: auricular branch of vagus nerve.
Tympanic membrane:
Medial aspect: tympanic plexus of glossophryngeal
nerve.
Lateral aspect: auriculotemporal of trigeminal nerve
and auricular branch of vagus nerve.
Tympanic cavity: tympanic plexus of
glossophryngeal nerve.
-Motor
Tensor tympani muscle: mandibular branch of
trigeminal nerve.
Stapedius muscle from facial nerve.
Physiology of the ear

1. Hearing
2. Equilibrium
 Mechaincal conduction
Sound --- drum ---- ossicles--- pressure changes in
labyrinthine fluids ---- basilar membrane ---- hair cells of
organ of Corti
 Transformation of mechanical energy to
electrical impulses by hair cells ( sensory )

Conduction of electrical impulses to the brain ( neural

pathway)
 I. Conduction of sound is
mediated by:
A) Lever action of the ossicles. The handle of
malleus is 1.3 times longer than long process
of the incus, providing a mechanical
advantage of 1.3.
b)Hydraulic action of tympanic membrane.
The area of tympanic membrane is much
larger than the area of stapes footplate, the
average ratio between the two being 21:1. As
the effective vibratory area of tympanic
membrane is only two-thirds, the effective
areal ratio is reduced to 14: 1 and this is the
mechanical advantage provided by the
tympanic membrane. The product of the areal
ratio and lever action of ossicles is
18: l.
 II. Transduction of mechanical energy to
electrical impulses:
 Movements of the stapes footplate, transmitted to
the cochlear fluids, move the basilar membrane,
setting up shearing force between the tectorial
membrane and the hair cells. The distortion of hair
cells gives rise to cochlear micro-phonics which,
trigger the nerve impulse. Higher frequencies are
represented in the basal turn of the cochlea and
the progressively lower ones towards the apex.
 III. Conduction of
electrical impulses to the
brain (neural pathways):
The produced electrical
impulses pass through the
auditory nerve and central
connections to the hearing
centre in the brain
(Temporal lobe).
 The vestibular system

(a) Peripheral; (semicircular ducts, utricle and

saccule) and the vestibular nerve.
 1. Cristae of the three semicircular ducts, their

receptors respond to angular acceleration.

 2. Maculae in utricle and saccule sense the position
of the head in response to gravity and linear
acceleration.
 3. Vestibular nerve which is made of the terminal

fibres from cristae and maculae.

 (b) Central; which is made up of the vestibular
nuclei and fiber tracts in the central nervous
system to integrate vestibular impulses with
other systems (eyes, joints and muscles) to
maintain body balance.
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