ANATOMY AND EMBROLOGY OF EAR

1. EAR
ANATOMY AND EMBRYOLOGY
1

2. DEVELOPMENT OF EAR
2

3. Auricle deveopement
• 1st branchial cleft
• Around 6th week- 6 tubercle appear around 1st brachial cleft coalesce form auricle
• Tragus - 1st arch rest from the 2nd arch
• Faulty fusion both arch lead to sinus and cyst seen b/w tragus and crux of helix
• 20th week pinna adult shape initially present low on the side of neck then moves up
more lateral and cranial
3

4. External auditory meatus
• 1st brachial cleft
• 16th week cells proliferate from bottom of ectodermal cleft and form metal plug
recanalizaation of this plug forms epithelial lining of the bony canal
• Recanalization begin near TM and proceed outwards hence Patricia common in outer
part
• 28th week external ear fully formed
4

5. Tympanic membrane
• All three germ layer
• Outer epithelial layer - ectoderm
• Middle fibrous layer -mesoderm
• Inner mucosal layer - endoderm
5

6. Middle ear cleft
• Endoderm of tubotympanic recess which intern arises from the 1st and partly from
2nd pharyngeal pouch
• Malleus and incus from mesoderm of 1st arch
• Stapes from 2nd arch except footplate and annular ligament derived from otic capsule
6

8. Membraneous Inner ear
• Starts at 3rd week
• Complete by 16th week
• Ectoderm tickens to form auditory palacode——->invaginate ——->otocyst
• This latter differentiate to form end-lymphatic duct and sac;utricle, the semicircular
ducted saccule and the cochlea
• Pars superior (semicircular canal and utricle) develop first then pars inferior (saccule
and cochlea)
• By 20 weeks cochlea developed sufficiently feats can hear in the womb of mother
8

11. Development of ear
11

12. ANATOMY OF EAR

13. ANATOMY OF EAR
• EXTERNAL EAR ( PINNA ,
EAC AND TM)
• MIDDLE EAR
• INTERNAL EAR
13

14. 14

17. PINNA OR AURICLE
• Single yellow elastic cartilage (except lobule/outer
ear).
• Elevation and Depression are seen on the lateral
surface.
• ANATOMICAL IMPORTANCE:
1. Incisura terminalis- cartilage deficiency between trigs
and crus of the helix- incision during surgery endured
approach.
2. Reconstructive surgery depression of nasal bridge
and defects of nasal ala.
17

18. PINNA OR AURICLE NERVE SUPPLY

19. PINNA OR AURICLE NERVE SUPPLY
19

20. EXTERNAL ACOUSTIC (AUDITORY) CANAL
• Bottom of concha to TM
• Size: 24mm posterior wall
• Two parts: (not straight tube)
1.Outer cartilaginous part ( upwards,
forwards, medially)- 1/3rd
2.Inner bony part (downward, forward,
medially)- 2/3rd
•To align the canal pinna is pulled
upwards, backwards and laterally.
20

21. OUTER CARTILAGINOUS PART OF EAC
• Outer 8mm
• Skin - thick and contain hair follicle,
ceruminous and pilosebaceous gland.
• FISSURE OF SANTORINI - deficit
through which paroti/superficial mastoid
infections transmit and vice versa.
• FURUNCLES (staphylococcus infection)
are seen only in the outer one-third of the
canal.
21

22. INNER BONY PART OF EAC
• Size: 16mm
• Skin lining is thin, devoid of haired ceruminous gland and
continuous over TM.
• ISTHMUS- narrowing at the bony meatus. ( foreign object
medial to isthmus is difficult to remove)
• ANTERIOR RECESS- a part of the bony auditory meatus
beyond the isthmus acts as a cesspool for discharge and debris
for external and middle ear infection
• FORAMEN OF HUSCHKE- deficiency at anteroinferior part in
children permitting infection to and from parotid.
22

23. EXTERNAL ACOUSTIC CANAL NERVE SUPPLY
• Anterior wall and roof : auriculotemporal N.
• Posterior wall and floor: auricular branch of
vagus
• Posterior wall of the auditory canal also
receives sensory fibres of VII through
auricular branch of vagus (CLINICAL
IMPORTANCE HERPES ZOSTER OTICUS
LESION ARE SEEN IN DISTRIBUTION OF
FACIAL NERVE- CONCHA , POSTERIOR
PART OF TM AND POST AURICULAR
REGION)
23

24. TYMPANIC MEMBRANE OR THE DRUMHEAD
• Forms partition between External auditory canal and Middle ear.
• Obliquely set
• Size : 9-10mm tall
8-9mm wide
0.1mm thick
• Parts of TM
1.Pars tensa
2.Pars flaccida
24

25. PARS TENSA
• Larger part
• ANNULUS TYMPANICUS: periphery
thickened fibrocartilaginous ring fits the
tympanic sulcus.
• UMBO: centre part tented inwards at the level
of tip of malleus.
• CONE OF LIGHT: radiating from the tip of
malleus to the periphery in anteroinferior
quadrant.
25

26. PARS FLACCIDA/SHRAPNELL’S MEMBRANE
• Situated above the lateral process
of malleus between the notch of
ravines and the anterior and
posterior malleal fold.
26

27. LAYERS OF TYMPANIC MEMBRANE
• Three layers,
1.OUTER epithelial layer- continuous with skin of meatus
2.INNER mucosal layer- continuous with mucosa of middle ear
3.MIDDLE fibrous layer (radial, circular and parabolic fibres)- encloses handle of
malleus - it is not well organised to various layers and thin in pars flaccida.
27

28. TYMPANIC MEMBRANE NERVE SUPPLY
• Medial surface: tympanic branch of glossopharyngeal nerve
• Lateral surface given in the diagram
28

29. LYMPHATIC DRINAGE OF EAR
29

30. MIDDLE EAR CLEFT
30

32. MIDDLE EAR CLEFT
• Middle ear cleft contains
1.Eustachian tube
2.Adieus and attic
3.Middle ear
4.Antrum
5.Mastoid air cells
• Lined by mucous membrane and filled with air.
• Middle ear is divided into three parts based
opposition of pars tensa as in the diagram.
32

33. THE MIDDLE EAR - WALLS
33

34. THE MIDDLE EAR
ROOF:
• Tegmen tympani, middle cranial fossa.
FLOOR:
• Jugular bulb seperated by thin plate of bone ( sometimes
congenitally deficient of this bone plate leading to jugular bulb
projecting into the middle ear separated only by mucosa)
ANTERIOR WALL:
• Internal carotid artery
• Two openings
1.Upper- canal for tensor tympani muscle
2.Lower- eustachian tube
34

35. THE MIDDLE EAR
POSTERIOR WALL:
• Mastoid air cell
• Pyramid - bony projection at summit tendon of the stapedius arises
• Aditus (lies above pyramid) - attic opens into antrum
• Facial nerve (just behind pyramid)
• Facial recess/posterior sinus (surgical importance intact canal wall
technique)
• Chords tympani
• Fossa incudes
• Sinus tympani present medial to pyramid
35

36. THE MIDDLE EAR - Posterior wall
36

37. THE MIDDLE EAR
MEDIAL WALL:
• Labyrinth
• Promontory (basal coil of cochlea) over which tympanic plexus present
• Oval window - footplate stapes fixed
• Round window/fenestra cochleae- secondary tympanic membrane
• Canal for facial nerve ( congenital absence of this canal leads to increased risk
for facial nerve injuries and infection )
• Prominence of lateral semicircular canal.
• Processus cochleariformis (marks the level of the first gene of facial n.)
• Sinus tympani lies medial to pyramid and it is bounded by subiculum below
and ponticulus above
37

38. THE MIDDLE EAR - medial wall
38

39. THE MIDDLE EAR
LATERAL WALL:
• Tympanic membrane
•Scutum
39

40. MASTOID ANTRUM
•Large, air-containing space at upper part of mastoid
•Roof - tegmen tympani
•Lateral wall - bone plate of 1.5cm thick this area is marked externally on the surface
of mastoid by suprameatal triangle (MacEwen’s triangle)
ADITUS AD ANTRUM:
•Aditus is an opening through which the attic communicates with the antrum
40

41. MACEWEN’S TRIANGLE:
41

42. THE MASTOID AND ITS AIR CELL SYSTEM
•Consist of bony cortex with a honeycomb of air cells underneath
•Three types of air cells ,
1.Well-pneumatized or cellular
2.Diplomatic
3.Sclerotic or acellular
•Antrum is always present irrespective of type of air cells present
42

43. THE MASTOID AND ITS AIR CELL SYSTEM
43

44. KORNER’S SEPTUM
•Persistence of the peterosquamosal suture as a bony plate.
•Separating superficial squamosal cells from the deep petrosal cells.
•Surgical importance : difficulty in locating the antrum and deeper cells.
44

45. OSSICLES OF THE MIDDLE EAR
•Three ossicles
1.Malleus (head, neck, handle/manubrium, a lateral and an anterior process)
2.Incus (body and a short process)
3.Stapes (head, neck anterior, and posterior crura, and a footplate)
•Conduct sound energy from the tympanic membrane to the oval window and then to
the inner ear fluid.
45

47. OSSICLES OF THE MIDDLE EAR
47

48. OSSICLES OF THE MIDDLE EAR
48

50. OSSICLES OF THE MIDDLE EAR
51

51. INTRATYMPANIC MUSCLES
•TWO MUSCLES
1.Tensor tympani (attaches to neck of malleus and tenses the tympanic
membrane)- mandibular nerve - 1st arch
2.The stapedius (attaches to the neck of stapes and helps to dampen very loud
sound also the smallest skeletal muscle)- 7th nerve - 2nd arch
52

53. TYMPANIC PLEXUS
•Lies on the promontory
•Formed by,
1.Tympanic branch of glossopharyngeal
2.Sympathetic fibres from the plexus round the internal carotid artery
•Supplies ,
1.Medical surface of TM
2.Tympanic cavity
3.Mastoid air cells
4.Bony part of eustachian tube
5.Also secretory function of parotid gland
54

54. TYMPANIC PLEXUS
55

55. MIDDLE EAR BLOOD SUPPLY
MAIN artery
•Anterior tympanic branch of maxillary artery which supplies tympanic membrane
•Stylomastoid branch of posterior auricular artery which supplies middle ear and
mastoid air cells
MINOR artery
•Petrosal branch of middle meningeal artery
•Superior tympanic branch of middle meningeal artery
•Branch of artery of pterygoid canal
•Tympanic branch of internal carotid
Veins drain into pterygoid venous plexus and superior petrosal sinus
56

58. THE INTERNAL EAR
59

61. THE INTERNAL EAR
•Organ of balance and hearing
•It consist of
1.Bony labyrinth
2.Membraneous labyrinth with clear fluid called endolymph
•The space between membraneous and bony labyrinth is filled with perilymph
62

62. THE INTERNAL EAR
BONY LABYRINTH
Consist of three parts vestibule, the semicircular canal and the cochlea
1.Vestibule:
•Central chamber
•Lateral wall has oval window
•Two recess spherical recess lodges the saccule and elliptical recess the
opening of aqueduct of vestibule
•In posteriosuperior part - 5 opening of semicircular canal
63

63. THE INTERNAL EAR
2.Semicircular canals:
•Three - lateral, posterior and superior
•Lies right angle to each other
•Two ends ampullated end and nonampullated end
•Crus commune - nonampullated end of posterior and superior canal
jointoformcommon channel
•Three canals open into the vestibule by five opening
64

64. THE INTERNAL EAR
3.Cochlea:
•Coiled tube making 2.5 to 2.75 turns round a central pyramid of bone- modiolus.
•Its base is directed towards internal acoustic meatus and transmit vessels and
nerve to cochlea
•Osseous spiral lamina divides the bony cochlea incompletely and gives
attachment to basal membrane
•Bony cochlea contains three parts Scala vestibule, Scala tympani and Scala
media
•Helicoterma the apex at which Scala vestibule and tympani communicate
•Scala tympani- secondary tympanic membrane(also connects with arachnoid
space by acqueduct of cochlea) ; scala vestiboli closed by footplate of stapes
65

65. THE INTERNAL EAR- bony labyrinth
66

66. THE INTERNAL EAR
MEMBRANOUS LABYRINTH:
It consist of the cochlear duct, the utricle and saccule, the semicircular ducts and the
endolymphatic duct and sac
1.COCHLEAR DUCT: (membraneous cochlea/scala media)
•Blind coiled tube
•Triangular on cross-section and its three walls of basilar membrane, the
Reissner’s membrane and the stria vascular
•Ductus reunions -connects cochlear duct and saccule
•The length of the basilar membrane increases as to the apical coil hence high
frequencies are heard at the basely at the apical
67

67. THE INTERNAL EAR
2.UTRICLE AND SACCULE:
•Utricle Posterior in bony labyrinth
•Receive 5 opening from 3 semicircular canals
•Uticulosaccular duct
•Macula -the sensory epithelium of the utricle- linear acceleration and
deceleration
•The saccule lies in the bony vestibule opposite to stapes footplate
•Saccule sensory epithelium is called macula its function not known
•In Ménière’s disease the distended saccule is surgically decompressed by
perforating the footplate
68

68. THE INTERNAL EAR
3.Semicircular ducts:
•Three in number opens into auricle
•Crista ampullaris -ampullated end of each duct contains a thickened ridge of
neuroepithelium
4.Endolymphatic duct and sac:
• End-lymphatic duct is formed by union of two ducts - saccule and utricle
• Passes through vestibular aqueduct
• Terminal part - endolymphatic sac (surgical importance for drainage or
shunt operation in Ménière’s disease )
69

69. THE INTERNAL EAR- membraneous labyrinth
70

70. THE INTERNAL EAR-
perilymphatic system where CSF passes into Scala tympani t
71

71. THE INTERNAL EAR
FLUIDS AND CIRCULATION:
1.PERILYMPH
•Resembles extracellular fluid rich in Na+
•Between bony and membraneous labyrinth
•Communicates with CSF via aqueduct of cochlea
•Formed by filtrate of blood serum and formed by capillaries of the spiral ligament
or a Direct continuation of CSF
72

72. THE INTERNAL EAR
FLUIDS AND CIRCULATION:
2.ENDOLYMPH:
•Fills entire membraneous labyrinth
•Resembles intracellular fluid rich in k+
•Secreted by secretory cells of stria vascular of the cochlea and by the dark cells
(present at utricle and semicircular canal)
•Flow is described in two views longitudinal floor radial flow
73

73. THE INTERNAL EAR - ORGAN OF CORTI
•The end organ for hearing
•Movement of the hair follicle cell in organ of
corti due to pressure changes produced by
ossicle on the perilymph and the
endolymph action potential is produced
74

74. THE INTERNAL EAR- blood supply of labyrinth
75

75. THE INTERNAL EAR- blood supply of labyrinth
• Venous drainage through 3 veins internal auditory vein, vein of cholera aqueduct
and vein of vestibular aqueduct which ultimately drains into inferior petrosal sinus
• And lateral venous sinus
76

76. LYMPHATIC DRAINAGE OF EAR
77

77. 78