otorhinolaryngology

10. ANATOMY OF MIDDLE EAR
 Development of middle ear
 Middle Ear Cleft
 Boundaries and Contents
 Epithelium
 Blood Supply
 Lymphatic Supply
 Nerves

11. DEVELOPMENT OF MIDDLE
EAR:
 During early stages of fetal
development a series of six visceral
arches appears on the lateral aspect
of head.
 The mesenchymal arches form
ridges in the overlying ectoderm
and corresponding projections in
the endoderm of the pharynx.
 The ridges become separated
from one another by a series of
furrows.
 The ectodermal furrows form
visceral clefts
 The endodermal furrows form
pharyngeal pouches.

12. TYMPANIC
MEMBRANE:
This has three layers:
a. An outer epithelial layer
from the ectoderm of the
cleft.
b. Middle fibrous layer from
the mesoderm between the
first visceral cleft and the
tubo tympanic recess.
c. An inner mucosal layer from
a part of the recess.

13. EUSTACHIAN TUBE AND TYMPANIC
CAVITY:
These are
developed from the
endoderm of the
tubotympanic recess
formed by the dorsal
part of the first
pouch receiving a
contribution from the
dorsal part of the
second pouch.

14.  First Arch(Mandibular Arch) –,
Malleus and Incus, Tensor Tympani
Muscle
 Second Arch(Hyoid Arch) –Stapes,
Stapedius Muscle
 Otic Capsule – Foot Plate of Stapes
and Annular Ligament
 Starts at third week ends at thirtieth
week
 Otic capsule mesenchyme
surrounding the derivatives of the
otocyst becomes dense and
chondrified to form otic capsule.
OSSCICLES AND MUSCLES:

15. TEMPORAL
BONE:
There are four
distinct elements which
become fused together.
1. Tympanic Ring
2. Squama
3. Styloid Process
4. Petromastoid

16. MASTOID
PROCESS:
The mastoid portion of the temporal bone is at
birth flat and stylomastoid foramen, lies immediately
behind the tympanic ring. As air cells develop, the
lateral part of the mastoid portion grows downwards
and forwards to form the mastoid process. Hence the
stylomastoid foramen comes to lie on the under
surface of the bone.

17. MIDDLE EAR
CLEFT: Tympanic Cavity
Compartments
Epitympanum:
Part lying above the level of short process of malleus
medial to the bone formed by horizontal part of the squama.
Mesotympanum:
Lying medial to the tympanic membrane.
Hypotympanum:
Below the drum head, medial to the tympanic plate.
 Aditus Ad Antrum
 Antrum
 Mastoid air cells
 Eustachian Tube

18. COMPARTMENTS OF MIDDLE
EAR

19. BOUNDARIES OF TYMPANIC
CAVITY:
 Irregular air filled
space within Temporal
Bone
 For descriptive
purpose may be thought
of as a box with four
walls, a roof and a floor

20. LATERAL
WALL:
 Partly bony and partly membranous
 Tympanic membrane forms central portion of lateral wall while above
and below there is bone forming outer lateral walls of Epitympanum and
Hypotympanum
 Thin and semi transparent
 Pearly Grey
 Obliquity of 55 degrees to the floor of meatus
 Longest diameter is 9 – 10 mm from postero superior to anterio inferior
while perpendicular shortest of 8 – 9 mm
 Has 3 layers – outer epithelial
- middle fibrous
- inner mucosal
 Pars Tensa
 Pars Flaccida
 Scutum

22. Three openings are present in the bone of the
medial surface of the lateral wall of tympanic cavity.
Posterior Canaliculus – for chorda tympani and
stylomastoid artery.
Petrotympanic(glaserian fissure) – opens anteriorly
receives anterior malleolar ligament and transmits
anterior tympanic branch of maxillary artery.
Anterior Canaliculus(canal of Huguier) placed at
medial end of petro tympanic fissure, chorda tympani
enters it.

23. MEDIAL WALL:
 It seperates Tympanic
Cavity from the inner ear
 Promontary rounded
elevation occupying much of
central portion of medial wall
formed by first turn of
Cochlea
 Fenestra vestibuli (oval
window) a kidney shaped
opening behind and above the
promontary closed by base of
Stapes and its surrounding
annular ligament. Size 3.25
mm long and 1.75 mm wide.


24. MEDIAL WALL:
 Just above the oval
window is horizontal
portion of facial nerve
lying in its bony
fallopian canal.
The ampullary end of
the horizontal semi
circular canal lies
above the facial canal.

25. FENESTRA COCHLEAE (ROUND
WINDOW):
Is closed by secondary tympanic membrane lies
below and behind fenestra vestibuli from
which it is seperated by a posterior extension
of the promontary called the Subiculum.
MEDIAL WALL

26. MEDIAL WALL
 PONTICULUS
A spicule of bone leaves the promontary above the
subiculum and turns to pyramids on posterior wall of
the cavity.
 PROCESSUS COCHLEARIFORMIS
The septum between the tubal orifice and canal for tensor
tympani is prolonged backwards along the medial wall
of the cavity as a shell of bone called Processus
Cochleariformis.

27. ANTERIOR WALL:
 Narrow as medial and lateral
wall converge.
 Lower portion is larger and
consist of a thin plate of bone
covering the carotid artery .
 The upper smaller part has
two parallel tunnels.
 The lower tunnel leads into
the bony portion of Eustachian
tube.
 Upper tunnel contains
tensor tympani muscle.

28. POSTERIOR WALL:
 Is wider above than below
and has in its upper part the
aditus which opens into
mastoid antrum
 Below is Fossa Incudis
which houses short process
of incus
 Below Fossa Incudis and
medial to the opening of
chorda tympani nerve is the
pyramid containing stapedius
muscle

29. FACIAL RECESS:
 Bounded medially by facial
nerve
 Laterally by tympanic annulus
but running through the wall
between the two is chorda tympani
nerve.
SINUS TYMPANI OR PYRAMIDAL
RECESS
Is a triangular recessed area that it
starts above at the oval window niche, it
occupies a groove deep to the
descending portion of the facial nerve
and to the pyramid and passes behind
the round window niche to the hypo
tympanum.

30. FLOOR:
Consists of thin plate of bone that seperates
the tympanic cavity from the dome of jugular
bulb.
ROOF
:
The tegmen tympani is the bony roof of the
tympanic cavity that separates it from the dura
of middle cranial fossa formed in by part of
petrous and part by squamous bone.

31. CONTENTS:
 Ossicles: Malleus
Incus
Stapes
 Muscles: Stapedius
Tensor tympani
 Nerves: Chorda tympani
Tympanic plexus

32. ADITUS AD
ANTRUM:
Leads backwards from
the upper attic space of
Epitympanum into the
mastoid antrum
 Medial Wall and Floor –
bony prominance of
lateral semi – circular canal
 Floor – Short process of
Incus
 Inferiorly – facial nerve

33. ANTRUM:
 Air filled sinus within the petrous
part of the temporal bone
 Roof – Tegmen Antri
 Lateral Wall corresponds to
Macewen’s triangle defined by Supra
mastoid crest a posterior
prolongation of upper border of the
root of Zygoma.
Vertical tangent through the
posterior margin of external meatus
and finally by the postero superior
margin of the external meatus itself.
 Floor – related to digastric muscle
laterally and sigmoid sinus medially.

34. MASTOID AIR
CELLS:
 May be classified as:
1. Cellular
2. Diploic
3. Sclerotic
80% of mastoids are pnuematized
20% diploic or Sclerotic
The following groups of cells may be
present:
1. Tip cells
2. Perisinus
3. Sino dural angle or petrosal
4. Perilabyrinthine
5. Superficial to dura
6. Zygomatic
7. Perifacial

35. EPITHELIUM:
 Eustachian tube
- Pseudo stratified ciliated epithelium in
cartilaginous part
- columnar in bony part
 Tympanic Cavity:
- ciliated columnar in anterior and inferior part
- cuboidal in posterior part
- Epitympanum and mastiod air cells flat non -ciliated

36. EUSTACHIAN TUBE:
- 36mm long
- Passes downwards forwards and medially
- Bony portion - lateral part
- 12 mm
- Narrowest part is isthmus
related medially to carotid artery and
superiorly to tensor tympani muscle
Cartilaginous portion:
- 24 mm
- Postero medial wall – cartilage fully
- Antero lateral wall partly cartilage and partly fibrous tissue
Muscles related:
- Tensor palati
- Levator palati
- Salphingo pharyngeus

37. EUSTACHIAN TUBE

38. BLOOD SUPPLY OF MIDDLE EAR:
BRANCH
Anterior tympanic
Stylomastoid
Mastoid
Petrosal
Superior tympanic
Inferior tympanic
PARENT ARTERY
Maxillary artery
Posterior auricular
Stylomastoid
Middle meningeal
Middle meningeal
Ascending pharyngeal
Branch from artery of
Pterygoid canal
Tympanic branches of
internal carotid
Lymphatics drain to
Retropharyngeal and
Parotid nodes.

39. FACIAL NERVE:

41. TYMPANIC PLEXUS:

43.  Branchial arches start to develop during 4th week.
 1st arch – MECKEL’S cartilage.
 2nd arch – REICHERT’S cartilage.
 Completion by 25th week.
1ST arch
derivative
2nd arch
derivative
Malleus , Incus ,
Mandible ,
Anterior malleolar
ligament
Stapes super
structure
Cartilage Post trematic
nerve
Mandibular
nerve V
Facial nerve
VII
Pre trematic
nerve
Chorda
tympani nerve
VII
Tympanic
branch IX

45.  4th week - Condensation in mesenchyme.
 Stapedial artery , Interhyale
 Foot plate develops from otic capsule.
 25th week - ossification completed and adult
size attained.
 Muscles develop from 1st & 2nd arch
mesenchyme.

47.  Mammalian ossicles – atrophied vestigial
remnants of reptilian
jawbone (mandible).
 Reptiles – only stapes present.
 Fossil records , Embryological studies
 Quadrate & Articular bones of developing reptile form
adult reptile jaw.
 In mammals they develop into anvil & hammer.
 Both proved to be 1st arch derivatives.

50. MALLEUS (HAMMER)
 Largest & most lateral ossicle
 Weight – 23 mg , Total length – 7.5 to 9.0 mm
• Head (caput)
• Neck
• Anterior process
• Lateral process
• Manubrium
Parts :

51. INCUS (ANVIL)
 Weight 25 – 30 mg ,
length of short process –
5mm , long process – 7
mm
•Body
•Short process
•Long process
•Lenticular
process – 4TH
OSSICLE
Parts :

52. STAPES (STIRRUP)
Parts : -
•Head
•Neck
•Crura
•Foot plate
Weight – 2.86 mg
Height – 3.26 mm
Length of foot plate
– 2.64 to 3.36 mm
Width of foot plate
– 1.14 mm
Area of foot plate -
1,65 to 3.76 sq. mm

54. MUSCLES ATTACHED TO
THE OSSICLES
STAPEDIUS: Origin : Pyramid.
Insertion: Neck of stapes.
Nerve supply: Facial nerve
TENSOR TYMPANI: Origin:Eustachian tube and sphenoid
Insertion: Handle of malleus
Nerve supply: Mandibular nerve
Actions

55. Ligaments attached to Ossicles :
MALLEUS  Anterior ligament
 Superior ligament
 Lateral ligament
INCUS  Posterior ligament
 Superior ligament
STAPES  Annular ligament

57. JOINTS OF THE MIDDLE EAR
 Incudomalleal joint – synovial saddle joint.
 Di arthrodial joint
 Concavo convex surfaces
 MOVEMENTS : Gliding motion
 The joint cavity is divided into
two incompletely by a wedge
shaped articular disk / meniscus

58. Incudostapedial joint –
 Synovial , ball & socket joint.
 MOVEMENTS : Stapes capable of
motion around an indefinite number of
axis with a common centre.
Stapes with oval window.

59. MUCOUS MEMBRANE
 Respi mucosa with cilia.Over ossicles flattened non-ciliated
It invests the ossicles , muscles , nerves , medial layer of TM
, reflected onto antrum & mastoid
POUCHES
 Pouch of Prussak
 Anterior recess
ofVon Troltsch
 Posterior recess
ofVon Troltsch

60.  Mainly by anterior tympanic & stylomastoid artery.
 Malleus & Incus – Ramus Nutricia Incudomallei artery.
 Incus by Incudal branch of anterior tympanic artery.
 Long & lentiform process and incudostapedial joint –
anastamosis around IS joint.
 Foot plate & crura – anterior tympanic artery.

61. FUNCTIONS OF THE MIDDLE EAR
 For normal hearing via the ossicles.
 Couples sound energy from ear canal to cochlea via TM
& ossicular chain.
 Physical protection for cochlea , Matches the impedance
of air to the higher impedance of cochlea
Applies sound preferentially to one window of cochlea
3 Roles : 1. Acoustic transformer
2. Impedance matching
3. Phase protection

63. INFLUENCE OF MIDDLE EAR
MUSCLES AND JOINTS
 Increase in stiffness of ossicular chain
 Change in direction of vibration of ossicles –
movement is less effectively coupled to cochlea
 Damp out unwanted resonance at high
frequencies

65. BONE CONDUCTION
Three routes contribute to bone conduction
hearing:
OUTER EAR- bone vibration is coupled to
the walls of the ear canal and the air within
it,also owing to the lag between vibration of
skull and mandible.
MIDDLE EAR- Lag of conductive apparatus and skull
vibrations,creating relative movement of stapes in oval
window.most important between 500 and 2000Hz. (Inertial
component)
 INNER EAR – due to movement of bony cochlea.The basilar
membrane is set in motion and perceived as sound.Mainly due
to relative motion of the inner ear fluids.

66. Middle ear mucosal folds & spaces

72. Prussak ‘s space

73. Embryology of EAR
Dr. Nanmullai.MS.ENT.

84. Thank you