DR MANPREET SINGH NANDA PROFESSOR ENT

1. EXTERNAL EAR
MIDDLE EAR
INNER EAR

2.  PINNA/ EAC/ TM

3.  Yellow elastic cartilage covered with skin
 Except Lobule (fat) and Incisura terminalis
(endaural incision)
 Lateral surface – folds and hollows
 Helix/ anti helix
 Tragus/ anti tragus
 Crus of helix
 Scaphoid fossa
 Triangular fossa
 Cavum concha
 Cymba concha

4.  Cartilage provides shape to auricle
 Skin of lateral side adherent to cartilage with
minimal subcutaneous tissue – FROST BITE
 Cartilage extends medially to form EAC
 Epithelium – stratified squamous, hair follicles,
sebaceous glands
 Medial surface/ cranial
 More sc tissue
 Skin loosely attached to cartilage – sebaceous
cyst/ abscess
 USED AS GRAFT IN RHINOPLASTY (CONCHAL) AND
TYMPANOPLASTY (TRAGUS/ CONCHA/ FAT
LOBULE

5.  Pinna connected to surrounding structures by
ligaments and muscles
 Ligaments – extrinsic/ intrinsic
 Muscles –
 Extrinsic – ant, post and sup auricularis
 Intrinsic – tragicus, anti tragicus, helicus major,
minor
 Facial N
 Blood supply
 ECA branches – post auricular artery, superficial
temporal and occipital
 Venous drainage - EJV, common facial vein

6.  Nerve supply of pinna
 Lateral surface
 Ant sup part, tragus, crus of helix – Auriculo
temporal nerve (V3)
 Lat concha, anti helix – facial nerve (VII)
 Concha – arnold’s nerve (X)
 Post part of lateral surface, lower part, lobule –
greater auricular nerve (C2,C3)
 Medial surface
 Upper 1/3 rd – lesser occipital nerve (C2)
 Lower 2/3 rd – greater auricular nerve (C2,C3)

8.  Only Cul – de – sac in the body lined by skin
 Extends from concha to TM
 S shaped, 24 mm, 8 mm (outer 1/3rd)
cartilaginous, 16 mm (inner 2/3rd ) bony
 Infants – cartilage part remains collapsed as bony
part not developed
 Cartilage part - Directed backwards, upwards,
medially, bony part – forwards, downwards,
medially
 Isthmus – narrowest part medial to junction, 5
mm from TM – FB impaction
 Bony part formed by temporal bone (tympanic
and squamous part)

10.  Carilage and bony part attached by fibrous tissue
 Skin – cartilaginous part – thick (both epidermis
and dermis), firmly adherent to cartilage,
contains hair follicles, ceruminous,
pilosebaceous glands
 Bony – skin thin, only epidermis no dermis, no
glands, hair follicles
 4 walls – roof, floor, anterior and posterior
 Floor and anterior wall are longer
 Ant wall proximal to TM joint, near TM forms a
blind pouch called Anterior Recess (FB,
discharge, debris)

11.  Bony canal – Anterio inferior area deficient –
Foramen of Huschke (till 4 years age) – parotid
infection
 Floor/ ant wall cartilage part – deficiencies –
Fissures of Santorini (two in number) – infection
from parotid and mastoid
 Relations
 Ant – TM joint, Parotid
 Post – Mastoid, Facial N
 Sup – Middle cranial fossa
 Inf – Parotid
 Medial – TM (oblique)
 Lateral - Concha

12.  Epithelial migration – self cleansing mechanism –
medial to lateral
 Lymphatic drainage
 Pre auricular LN (ant wall)
 Post auricular LN (post wall)
 Retro auricular/ Infra auricular LN (floor and
lobule)
 Nerve Supply
 Anterio superior part – Auriculo temporal nerve
(V3)
 Posterio inferior part – Arnold’s nerve (X) – cough
reflex

14.  Thin, semi transparent, pearly white, lying
obliquely medial to EAC, 55 degree to floor
 Forms lateral wall of middle ear
 Separates external and middle ear
 Vertical diameter 9-10mm, AP diameter 8-9 mm,
thickness 0.1-0.15 mm
 Parts
 Pars tensa – pearly white, below malleolar folds
 Contains 3 layers – outer epithelial continous
with skin of EAC, Middle fibrous contains inner
circular, outer radial and parabolic fibres and
inner mucosal continous with middle ear mucosa

15.  Peripheral part thickened and made of
fibrocartilaginous ring called annulus tympanicus
 Deepest part in middle – umbo attached to
handle of malleus
 Can be divided into 4 quadrants – ant sup, ant
inf, post sup and post inf
 Ant inf part illuminated when light reflected on
TM – light reflex (cone of light)
 Pars flaccida/ Shrapnell’s membrane
 Pinkish triangular area fits in notch of rivinus
above malleolar folds, no middle fibrous layer –
thin No annulus tympanicus
 Short/lateral process of malleus

18.  Blood supply
 Outer (lateral surface) – Manubrial artery,
Maxillary artery – deep auricular branch
 Inner (Medial surface – Maxillary artery –
anterior tympanic branch, stylomastoid
artery – posterior tympanic branch,
ascending pharyngeal artery – inferior
tympanic branch, middle meningeal artery
 Venous drainage
 Outer surface – EJV
 Inner surface – Transverse sinus, venous
plexus around ET

19.  Nerve Supply
 Outer surface – Auriculo temporal nerve
supplies the anterior ½
 Arnold’s nerve – posterior 1/2
 Inner surface – Tympanic plexus – Jacobson’s
N (IX)

20.  MIDDLE EAR CLEFT
 Tympanic cavity along with Eustachian tube,
aditus ad antrum, mastoid antrum and
mastoid air cells
 Filled with air

21.  Pharyngo tympanic tube
 Connects Tympanic cavity to Nasopharynx
 Equals/maintains pressure in tympanic cavity
 36 mm long
 2 parts – upper 1/3rd bony – tympanic part(12
mm)
 Lower 2/3rd cartilage – nasopharyngeal part ( 24
mm)
 The two parts meet at isthmus (narrowest part) –
160 degree angle at junction
 Nasopharyngeal part – closed at rest/collapsed ,
opens on yawning, present behind the post end
of inferior turbinate, narrowest at this end
 Torus tubaris, Fossa of rosenmuller

22.  Ostmann’s pad of fat – fibrofatty tissue in
relation to nasopharyngeal part, keeps ET
closed, protects from nasopharyngeal reflux and
secretions
 Tubal tonsils – hypertrophy causes ET obstruction
 Infants
 ET wider, shorter, more horizontal
 Tubal cartilage is flaccid
 Less ostmann’s fat
 Length 13-18 mm, bony part longer than 1/3rd –
milk can enter during feed – head up position

23.  Muscles – Tensor palati (V3), Levator palati,
Salpingopharyngeus (Pharyngeal plexus)
 Epithelium – pseudostratified ciliated columnar
 Nerve supply – Tympanic plexus
 Blood supply – ascending pharyngeal artery,
middle meningeal artery, artery of pterygoid
canal
 Venous drainage – Pterygoid plexus
 Functions
 Ventilation of middle ear cleft, equalises middle
ear pressure with atmospheric pressure
 Prevents reflux of nasopharyngeal secretions into
middle ear
 Drainage of middle ear secretions

25.  Biconcave irregular space in petrous part of
temporal bone filled with air
 Vertical diameter and AP diameter – 15 mm
 Transverse diameter – 6 mm at upper part,
2mm at center and 4 mm at lower part
 Six sided – roof, floor, ant wall, post wall,
medial wall, lateral wall
 Three parts – epitympanum, mesotympanum,
hypotympanum
 Three ossicles (tiny bones) – malleus, incus,
stapes
 Two muscles – tensor tympani, stapedius

27.  Epitympanum – attic – above malleolar folds of TM,
medial to pars flaccida
 Contains head of malleus, body and short process of
incus, incudo malleolar joint
 Connects with mastoid antrum via aditus – posteriorly
 Connects with mesotympanum via isthmus tympanic
anticus and posticus
 Lined by pavement epithelium (cuboidal)
 Mesotympanum – medial to pars tensa
 Anterior mesotympanum – connects with nasopharynx
via ET – respiratory epithelium
 Protympanum – around ET
 Hypotympanum – below level of TM, resp epithel

28.  Ventilatory anatomy
 Nasopharynx ---air-- ET ------ Anterior
mesotympanum ----Isthmus tympanic
anticus ---- Anterior epitympanum -----
 1 Posterior epitympanum ----- Isthmus
tympanic posticus ----- Posterior
Mesotympanum ----- Hypotympanum
 2 Posterior epitympanum - Aditus --
Mastoid antrum and air cells ----Posterior
wall ---- Hypotympanum

29.  Walls
 Roof – tegmen wall separates from middle
cranial fossa, thin plate of bone – tegmen
tympani
 Floor – Thin plate of bone separates from IJV
bulb located in jugular fossa, can be
deficient
 Lateral wall
 TM – separates from external ear
 Scutum or outer attic wall – made up of
squamous part of temporal bone, upper part
of lateral wall

30.  Medial wall/labyrinthine wall
 Separates middle ear from inner ear
 Promontory – bony round bulge of medial wall by
basal turn (coil) of cochlea, most prominent part
 Tympanic plexus lies on promontory
 Bony lateral semicircular canal – post sup to
promontory, above oval window
 Fenestra vestibuli (oval window) – between
middle ear and scala vestibuli of cochlea, post
sup to promontory, foot plate of stapes is placed
in the window, fixed by annular ligament
 Size 3.25*1.75 mm
 Ponticulus and Subiculum – bony ridges in medial
wall

31.  Fenestra cochlea (round window) – post inf
to promontory, separates middle ear from
scala tympani of cochlea, closed ny
secondary membrane, size 1.5*1.3mm
 Processus cochleariformis – hook like
projection ant to oval window, tendon of
tensor tympani related to it, genu of facial
nerve lies here – denotes the start of
horizontal part of facial nerve
 Facial nerve – lies in bony fallopian canal
below oval window – horizontal part of facial
nerve

33.  Anterior wall
 Separate middle ear cavity from ICA
 Thin plate of bone
 Openings
 Upper – canal for tensor tympani muscle
 Lower – ET
 Canal for chorda tympani nerve – canal of
Huguier
 Opening of carotid canal – glasserian fissure
 Anterior malleolar ligament
 Anterior tympanic artery

34.  Posterior wall/ Mastoid wall
 Opening of aditus – upper part
 Pyramidal eminence/ processus pyramidalis –
triangular bony projection, stapedius muscle
tendon related to it
 Vertical portion of facial nerve – courses along
post wall to exit in stylomastoid foramen
 Facial recess – suprapyramidal recess – direct
assess can be made through it via post
tympanotomy approach via mastoid without
disturbing the post meatal wall
 Collection of air cells lying lateral to facial nerve
 Bounded by chorda tympani n, pyramid, post
wall, fossa incudis

36.  Sinus tympani/ infra pyramidal recess
 Medial to pyramid
 Mc location for cholesteatoma persistance
even after surgery
 Separated from facial recess by pyramid
 Fossa incudis – contains short process of incus
 Opening for exit of chorda tympani nerve
present in post wall

37.  Relations of middle ear cleft
 Laterally – External ear
 Medially – Inner ear
 Anteriorly – ICA
 Floor – jugular bulb
 Roof – tegmen plate
 Posteriorly – lateral sinus
 Nerves related to middle ear cleft
 V, VI CN – close to apex of petrous pyramid
 VII CN – horizontal part (medial wall),
vertical part (posterior wall)

38.  OSSICLES
 3 tiny bones, conduct sound energy from TM to
oval window
 Malleus (Hammer)
 Largest and lateral most ossicle
 8-9 mm long, 23-25 mg weight
 Contains head, neck, handle, lateral process
 Head lies in epitympanum
 Lateral process – knob like pojectionon outer
surface of TM providing attachment to anterior
and posterior malleolar folds, projects laterally
from neck of malleus

40.  Incus (Anvil)
 25-30 mg
 Contains body, short process and long process
 Body – lies in epitympanum, articulates with
head of malleus
 Short process – projects into epitympanum
 Long process – projects downwards behind
handle of malleus, articulates with head of
stapes via lenticular process and forms
incudo stapedial joint

41.  Stapes (Stirrup)
 Smallest ossicle
 3.5 mm
 Contains head, neck, foot plate, ant crura
and post crura
 Foot plate attached to oval window by
annular ligament
 ALL OSSICLES ARE SUPPLIED BY ANTERIOR,
INFERIOR AND POSTERIOR TYMPANIC ARTERIES

42.  MUSCLES OF MIDDLE EAR
 Tensor tympani
 Tenses the TM, decreases the movement of
ossicles so dampens loud sound before it enters
inner ear
 Muscle for malleus, 1st arch muscle, supplied by
mandibular nerve (V3), inserted into neck of
malleus
 Stapedius
 Dampens loud sound
 Muscle for stapes, 2nd arch muscle, supplied by
nerve to stapedius (VII), inserted into neck of
stapes

44.  NERVES OF MIDDLE EAR
 Chorda tympani
 Branch of facial nerve, enters tympanic
cavity from posterior wall --- runs forwards
medial to malleus and lateral to incus, runs
on medial surface of TM ---escapes through
anterior wall
 Carries taste fibres from ant 2/3rd of tongue
 Carries p.s secretomotor fibres to
submaxillary and sublingual salivary glands

45.  Tympanic plexus
 Lies on promontory
 Innervates the medial surface of TM, mastoid air
cells, tympanic cavity, bony ET
 Carries secretomotor fibres to parotid gland
 Formed by
 - Jacobson’s nerve (IX) – sensory supply
 Plexus around ICA
 Motor supply – tensor tympani (V3), Stapedius
(VII)
 Mastoid antrum – Meningeal branch of
mandibular nerve (V3)

46.  Blood supply
 ECA – maxillary artery, stylomastoid artery,
ascending pharyngeal artery and middle
meningeal artery
 ICA – carotico tympanic artery
 Venous drainage
 Ptreygoid venous plexus, sup petrosal sinus,
sigmoid sinus
 Lymphatic drainage
 Pre auricular ln, retropharyngeal ln, upper
deep cervical ln

47.  Greek word “resemblance to breast”
 Air containing space in petrous part of
temporal bone
 9mm height, 14 mm width, 7 mm depth
 Not at birth, develop at 1 yr age, adult size
at puberty (Facial N directly exposed)
 Aditus ad antrum
 Short canal connecting epitympanum to
mastoid antrum
 Facial nerve, short process of incus lie on
floor

48.  Mastoid antrum
 Largest air cell of mastoid bone
 Ant – Aditus ad antrum
 Post inf- communicates with mastoid air cells
 Medially – post scc
 Lateral wall – cortex of mastoid bone, 1.5 cm
thick
 Roof – Tegmen antrum, separates from
middle cranial fossa
 Floor – formed by mastoid bone

49.  Antrum lies 15 mm deep
 Clinically palpable at Cymba concha
 Mac Ewen’s triangle/ Suprameatal triangle
 Bony surface landmark of antrum
 Spine of henle lies in the triangle
 Bounded by
 Temporal line of suprameatal crest – linea
temporalis – ridge extends from zygomatic
process
 Post sup meatal wall
 Line connecting the two tangent to post margin
of EAC

51.  Mastoid air cells
 Types of mastoid
 - Cellular – well pneumatized – numerous
large air cells – honey comb appearance -
80%
 - Sclerotic – acellular – absent air cells – due
to ET blockage – 20%
 - Mixed – diploeic – small and less numerous
air cells – narrow spaces
 Pneumatization begins in 1st year of life and
is completed by 4-6 years of age

53.  Classification of mastoid air cells
 A) Peripheral – dural, sinodural, perisinus, tip,
retrofacial
 B) Central – periantral
 C) Accessory – peritubal, styloid, zygomatic,
squamous, occipital
 Korner’s septum
 Persistant petrosquamous suture line/ bony plate
between petrous and squamus part of temporal
bone which separates squamous cells and
petrosal cells
 Causes difficulty in locating the antrum and
deeper cells

56.  Articulates with 5 cranial bones – parietal,
sphenoid, occipital, zygomatic, mandibular
 Forms base and lateral side of skull
 Pyramidal shaped
 Parts – squamous, petrous, tympanic and mastoid
 Petrous part separates middle and posterior
cranial fossa
 Contents
 Bony part of external, middle eear including
ossicles, inner ear
 Bony covering for sigmoid sinus and jugular bulb

57.  Fallopian canal containing facial nerve
 Osseous canal containing ICA

58.  Mixed nerve – sensory, motor, secretomotor
fibers
 From pons to parotid
 Sensory – nerve of wrisberg (nervus intermedius)
– solitary tract nucleus in medulla – carries taste
sensation from ant 2/3rd of tongue (afferent
fibers) / general sensation from skin of concha,
EAC, TM
 Secretomotor – sup salivary nucleus in pons –
secretomotor to lacrimal, submandibular,
sublingual, nasal and palate glands (efferent
fibers)
 Motor – motor facial nucleus in pons – supplies
muscles of facial expression

59.  Parts
 Supranuclear
 Infranuclear
 SUPRANUCLEAR/ INTRACRANIAL (15-17 mm)
 Motor fibers from Pons nucleus – hook around VI
CN nucleus – travel through CP angle along with
sensory fibers and VI and VIII CN – leave brain
stem at ponto medullary junction
 Upper part of nucleus – innervate forehead
muscles – receive fibers from both cerebral
cortex (tracts both crossed and uncrossed)
 Lower part of nucleus – innervate lower face –
receives fibers from opposite cerebral cortex (
crossed fibers)

61.  Infranuclear
 Intratemporal
 Extratemporal
 INTRATEMPORAL
 IAM – stylomastoid foramen
 Parts
 Intrameatal
 Labyrintine
 Tympanic
 Mastoid

62.  Intrameatal part
 Within IAC 8-10mm
 Passes along with VIII CN and internal auditory
artery
 At fundus of IAC – sensory and motor fibers
combine and enter fallopian canal
 Labyrinthine part
 From fundus of IAC – geniculate ganglion 3-5mm
 Narrowest part at entry of labyrinthine part (0.6
mm)
 Geniculate ganglion – 1st genu – here facial nerve
takes a posterior turn
 Intrameatal part and labyrinthine part together
form the petrous portion of facial nerve

64.  Tympanic part
 Enters middle ear at geniculate ganglion
(processus cochleariformis)
 Geniculate ganglion – oval window
 Horizontal part 10-12 mm
 At oval window (pyramid) nerve turns inferiorly
– 2nd genu
 Mastoid part
 Vertical part 10-14 mm
 Oval window – stylomastoid foramen
 Intracranial – from nucleus to stylomastoid
foramen

65.  Extratemporal/ Extracranial
 From stylomastoid foramen to parotid
 Crosses the styloid process and divided into
terminal branches in face
 BRANCHES
 Greater superficial petrosal nerve – arises at
geniculate ganglion – carries secretomotor fibers
to lacrimal glands and glands of nasal mucosa
and palate, also brings taste fibers from hard
and soft palate – 1st branch
 Nerve to stapedius – arises at 2nd genu(
pyramidal eminence)- carries motor fibers to
stapedius muscle

67.  Chorda tympani – arises from middle of mastoid
segment near stylomastoid foramen – carries
secretomotor fibers to submandibular and
sublingual gands. Also brings taste fibers from
anterior 2/3rd of tongue
 Muscular branches after exiting stylomastoid
foramen
 Posterior auricular nerve – supplies muscles of
pinna, occipital belly of occipito frontalis muscle
 Digastric branch – to post belly of digastric
 Stylohyoid branch – to stylohyoid muscle

68.  Terminal branches
 After crossing styloid process
 Upper temporofacial branch
 Temporal branch – supplies muscles of
auricle, upper orbicularis oculi, frontalis,
procerus – raises the eyebrow
 Zygomatic branch – supplies lower
orbicularis oculi – tight shutting of eyes
 Buccal branch – middle part of face, muscles
of nose, upper orbicularis oris, buccinator –
showing of teeth

70.  Lower cervicofacial
 Mandibular branch – lower orbicularis oris,
muscles of lips and chin – whistling
 Cervical branch – supplies platysma –
contraction of platysma
 BLOOD SUPPLY
 At CP angle – Ant inf cerebellar artery
 IAC – labyrinthine artery
 Geniculate ganglion – sup petrosal artery
 Tympanic and mastoid segment –
stylomastoid artery

71.  Communications
 IAC – VIII CN
 Geniculate ganglion – X CN (auricular branch)
 Outside stylomastoid foramen – IX, X, greater
auricular nerve (C2,C3), Auriculotemporal
nerve (V3)
 Lesser occipital nerve (C2)
 Neck – cervical cutaneus nerve

72.  In petrous part of temporal bone b/w middle
ear and IAC
 Parts
 Bony labyrinth
 Membranous labyrinth
 Perilymph – fluid b/w bony and membranous
 Endolymph – fills membranous labyrinth
 Has organs of both hearing and equilibrium

74.  3 parts
 Bony Vestibule
 Bony Semicircular canals (SCC)
 Bony Cochlea
 Bony Vestibule
 Ovoid central part of bony labyrinth
 5mm X 3mm
 Lateral wall – related to middle ear, has bean
shaped opening – fenestra vestibuli (oval
window) closed by foot plate of stapes and
surrounded by annular ligament

75.  Medial wall – related to IAC
 Anteriorly or front ½ - marked depression called
Spherical recess (lodges the saccule)
 Posteriorly or behind – another depression called
Elliptical recess (lodges the utricle)
 Below elliptical recess – diverticulum called
Vestibular aqueduct – through it passes the
endolymphatic duct
 Spherical and Elliptical recess are separated by
Vestibular crest – splits inferiorly to enclose
Cochlear recess (for cochlear nerve filaments)
 Post part of vestibule – 5 openings of SCC
 Anteriorly – lies cochlea

77.  Medial wall is perforated by minute holes
called Macula cribrosa – for passage of
vestibular nerve

78.  BONY SEMICIRCULAR CANALS
 Posterior part of bony labyrinth
 3 canals – superior(anterior), posterior
(vertical), lateral (horizontal)
 Each canal 2/3rd of a circle
 Diameter 0.8 mm
 Lie at right angle to each other
 Contain membranous semicircular ducts
 Contain 2 ends – ampullated (dilated) and
non ampullated. Both open into vestibule
 Ampulla contains sensory epithelium

80.  Superior or anterior SCC
 Length 15-20 mm
 Ampullated ends opens into lateral part of vestibule
 Non ampullated end fuses with non ampullated end
of posterior scc to form a common opening called
crus commune – opens into medial part of vestibule (
so total 5 openings into vestibule)
 Forms arcuate eminence on petrous part of temporal
bone
 Posterior or vertical SCC
 18-22 mm
 Ampullated end (lower end) – opens into lower part
of vestibule
 Non ampullated (upper end) – forms crus commune

81.  Lateral/horizontal SCC
 Forms a round bulge into aditus and antrum
of middle ear
 Length 12-15 mm
 Ampullated/anterior end – opens into upper
part of vestibule
 Non ampullated/ posterior end – opens into
lower part of vestibule (below opening of
crus commune)
 Solid angle – angle formed by all 3 SCC

82.  BONY COCHLEA
 Anterior part of labyrinth
 Coiled tube like a snail
 30-35 mm long, 5 mm from base to apex, 9 mm
across its base
 Has 2 3/4 turns around a conical central
pyramid of bone called Modiolus (has
perforations for cochlear nerve)
 Basal turn of cochlea – promontory in medial
wall of middle ear
 Within it lies membranous cochlea
 Osseous spiral lamina – thin plate of bone
projects into modiolus, divides cochlea into 3
compartments (longitudinal channels)

83.  Scala Vestibuli – above – communicates with
middle ear through oval window, closed by
foot plate of stapes
 Scala Tympani – below – communicates with
middle ear through round window, closed by
secondary tympanic membrane
 Both of these communicate with each other
at apex of cochlea through helicotrema
 Filled with perilymph
 Scale Media – Cochlear duct – in between –
part of membranous cochlea

86.  Membranous vestibular labyrinth
 Membranous semicircular ducts
 Membranous cochlear duct
 Contains endolymph
 Lies within bony labyrinth floating on
perilymph
 Membranous Vestibule
 Contains
 Saccule
 Utricle
 Endolymphatic duct and sac

88.  Saccule – globular in shape
 Lies in anterio inferior part, occupies spherical
recess
 Connected to cochlear duct by membranous
ductus reuniens
 Connected to utricle by utriculo saccular duct
which forms endolymphatic duct and ends up in
endolymphatic sac
 Utricle – oblong and irregular in shspe
 Lies in posterio sup part, occupies elliptical
recess
 Connected to 3 semi circular ducts by 5 openings
 Bigger than saccule

89.  Macula
 Vestibular receptor organ
 Neuroepithelial organ of saccule and utricle
 For static balance, responds to gravitational
changes and linear acceleration and deceleration
 Composed of hair cells (saccule – 18000, utricle –
33000) and supporting cells
 Hair cells – type I – centre part (flask shaped)
type II – peripheral part (cylindrical shaped)
 Also contains a gelatinous mass composed of
muco ps and calcium carbonate secreted by
supporting cells – otolith/ statoconia/ otoconia

91.  Semicircular ducts
 Within scc
 Ampullated end contains neuroepithelium
called cristae (saddle shaped)
 Contains hair cells and supporting cells
 Gelatinous mass is called cupula
 Hair cells contain one large kinocilium and
65-110 small steriocilia
 Responds to angular acceleration and
deceleration
 Organ for kinetic balance

92.  MEMBRANOUS COCHLEA/ COCHLEAR DUCT/ SCALA
MEDIA
 Occupies mid portion of cochlear canal
 Connected to saccule through ductus reuniens
 Anterior most part
 Triangular shape
 Boundaries
 Floor – Basilar Membrane – supports Organ of Corti
 Roof – Reissner’s Membrana – separates it from Scala
Vestibuli
 Lateral wall – Stria Vascularis – secretes endolymph,
contains vascular epithelium, maintains ionic
composition and electronic potential of endolymph

93.  Organ of Corti
 Neuroepithelium situated on the basilar
membrane
 Sensory organ of hearing
 Spread like a ribbon along entire length of
basilar membrane
 Contains 2 rows of rods of inner and outer hair
cells
 Inner hairs cells – one row – 3500, flask shaped
 Outer hair cells – 3-4 rows – 12000, cylindrical
 Hair cells are receptor cells of hearing, convert
sound energy -> electrical energy

94.  Terminal fibres of cochlear nerve are in contact
with hair cells
 Hair cells are separated by supporting cells and
dieter cells
 Tectorial Membrane – overlies organ of corti,
contain gelatinous material
 Sheering force between organ of corti and
tectorial membrane – cxause hair cell
stimulation
 Organ of corti contains cortilymph( resembles
perilymph)
 No blood supply. Depends on stria vascularis for
oxygen

97.  Inner ear fluids
 Perilymph – fills the space between bony and
membranous labyrinth, resembles ECF and
CSF, plasma
 Rich in sodium ions, proteins, glucose
 CSF reach labyrinth via cochlear aqueduct
 Endolymph – fills membranous labyrinth,
resembles ICF
 Rich in potassium ions
 Secreted and absorbed by stria vascularis and
endolymphatic sac

98.  ENDOLYMPHATIC DUCT AND SAC
 Ducts from utricle and saccule form utriculo
saccular duct -> this continues as
endolymphatic duct (passes through
vestibular aqueduct) -> terminal part dilated
to form endolymphatic sac
 Regulates pressure of membranous labyrinth
 Role in reabsorption and regulation of
endolymph

100.  ARTERIAL SUPPLY
 Basilar artery -> Ant inf cerebellar artery ->
Internal Auditory Artery
 3 branches
 Ant vestibular artery – supplies utricle,
superior and lateral scc
 Vestibulo cochlear artery –
 1. posterior vestibular artery – supplies
saccule, post scc
 2. cochlear branch – supplies cochlea (10%)
 Main cochlear artery – supplies cochlea (90%)

102.  VENOUS DRAINAGE
 Internal auditory vein, vein of cochlear
aqueduct, vein of vestibular aqueduct ->
labyrinthine vein -> inferior petrosal sinus,
sigmoid sinus, lateral venous sinus

103.  Lined by dura
 Length – 1 cm
 In petrous part of temporal bone
 Medial end – related to inner ear
 Lateral end – has numerous apertures for
 - VII CN
 - VIII CN
 - Internal auditory artery
 - Internal auditory vein

105.  In IAC – divides into
 Anerior – Cochlear N
 Posterior – Vestibular N
 COCHLEAR NERVE
 Fibres of cochlear nerve from IAC reach the
modiolus to form spiral ganglion
 Bipolar cells of spiral ganglion of cochlear
nerve innervate the hair cells of organ of
corti (95% IHC, 5% OHC) to form the auditory
pathway

106.  Vibration of stapes footplate -> movement of
inner ear fluids -> displaces basement membrane
-> stimulates organ of corti
 1st order neurons – spiral ganglion of cochlear
nerve
 Gives 2 processes
 Peripheral process – innervates hair cells of
organ of corti
 Central process – terminates in dorsal and
ventral i/l cochlear nuclei (2nd order neurons)
 Terminate into lateral lemniscus on both sides
(u/l and c/l)

107.  Terminates into sup olivary nucleus (c/l or
i/l) – 3rd order neurons
 Terminates into inf colliculus (c/l or i/l) – 4th
order neurons
 Terminates into medial geniculate body of
thalamus – 5th order neurons
 From here axons pass into auditory cortex in
cerebrum
 Area of cortex associated with hearing –
Brodmann’s area - 41

109.  Emerges in post part of IAC where it forms
scarpa’s ganglion containing bipolar cells of
vestibular nerve which form the vestibular
pathway
 Vestibular nerve divides into
 Superior vestibular nerve – innervates macula
of utricle and anterior part of saccule and
cristae of anterior and lateral semicircular
ducts
 Inferior vestibular nerve – innervates macula
of posterior part of saccule and cristae of
posterior semicircular ducts

110.  Scarpa’s ganglion form 1st order neurons
 Terminate into vestibular nuclei in floor of
IVth ventricle which forms the 2nd order
neurons
 Vestibular nuclei – superior (receives fibres
from semicircular ducts), inferior, medial and
lateral nuclei (receives fibres from utricle
and saccule)
 Vestibular nuclei terminate into Oculomotor
nuclei (3rd order neurons)
 Terminate into effector organs (ocular and
postural)

111.  Efferent from vestibular nuclei into
 ANS – responsible for nausea, vomiting,
sweating
 Motor part of spinal cord – coordination
movements of head, neck and body
 Cerebellum – maintain body balance
 External ocular muscles

113.  Branchial apparatus (4th and 5th week)
 Consists of
 Branchial arches (pharyngeal)
 Clefts or groove on outer aspect
 Pouches on inner aspect
 Cervical and occipital myotomes

114.  Development of sound conducting apparatus
(External Ear and Middle Ear) and sound
perceiving apparatus (Inner Ear) is from
different structures and independent of each
other
 EXTERNAL EAR AND MIDDLE EAR
 PINNA
 From six tubercles/hillocks of His around 1st
branchial cleft
 1st tubercle of His from 1st branchial arch
leads to formation of tragus
 2nd to 6th from 2nd branchial arch

115.  Starts at 6th week of IUL completed at 20th
week
 Defective fusion of 1st and 2nd arch –
preauricular sinus
 Failure deveopment of tubercles – anotia
 Failed development of 4th tubercle – anti
helix defect – bat ear deformity
 EAC
 Develops around 1st branchial cleft between
8th and 10th week of IUL

117.  TYMPANIC MEMBRANE
 Develops from membrane separating 1st
branchial cleft and 1st pharyngeal pouch
 From all 3 germinal layers
 Outer epithelial layer – from ectoderm
 Middle fibrous layer – from mesoderm
 Inner mucosal layer – from endoderm
 TYMPANO MASTOID CAVITY
 From tubotympanic recess (1st pharyngeal pouch)
 Eustachian tube – from proximal narrow part
 Middle ear – from distal dilated part

118.  Ossicles
 Malleus and Incus – from mesoderm of 1st
arch
 Stapes suprastructure – from 2nd arch
 Stapes footplate and annular ligament – from
otic capsule

119.  Starts in 3rd week of IUL and completed by 16th
week
 Develops from otic capsule
 Thickening of ectoderm of hind brain ->
 Formation of Otic Placode ->
 Invaginates into otocyst (otic cyst or capsule)
 Differentiates to form Membranous labyrinth
 Mesoderm around otic capsule -> leads to
formation of bony labyrinth
 Development of pars superior – utricle and SCC
much earlier than pars inferior – saccule and
cochlea