Coupon Accepted Successfully!


Inner Ear

--> Otic capsule develops from 14 ossifying Centres & which complete fusion by 20 wk

Intrauterine life.
External Ear

  1. Pinna
    1. Framework: Yellow elastic cartilage except lobule.
    2. Applied Aspect: Cymba concha: Beneath this lies the MacEwen’s triangle, a landmark for the mastoid antrum.
    3. Incisura terminalis: Area between the crus of the helix and tragus
    4. Is devoid of cartilage
    5. Area is used in incision of endaural approach. The other approaches are post aural and trans meatal.
  2. Auricular Cartilages:​
    1. Tragus- Myringoplasty, Rhinoplasty
    2. Perichondrium- Myringoplasty
    3. Fat (Lobule)- Myringoplasty
    4. Concha- Rhinoplasty, Alar repair
Innervation of the pinna
  1. Auricular branch of auriculotemporal (CN V)
  2. Greater Auricular
  3. Vagus (auricular branch)
  4. Lesser Occipital
  5. Auricular branch of Auricular nerve (also supplies anterior and superior wall of the meatus)
  6. Greater auricular nerve
  7. Auricular branch of the vagus (concavity of concha, posterior and inferior wall of the meatus)
  8. Facial nerve (concavity of concha, posterior superior wall of E.A.C.)
  1. External Auditory Canal (E.A.C)
    1. Length: 24-25 mm. 2 constrictions
    2. Parts: Lateral 1/3: Cartilaginous
    3. Shape: “S” shaped curve
    4. Cartilaginous part: direction, medially upwards and backwards
    5. Deficient: Postero-superiorly
    6. Has fissures: In the anterior part (2-3 deep fissures) (Fissures of santorini)
    7. Has ceruminous glands (modified apocrine sweat glands)
Nerve Supply: Nerves for EAC: C3, 7, 10,5
  1. Anterior and antero-superior wall: auriculo temporal nerve
  2. Floor and posterior wall: Auricular branch of Vagus (Arnold’s nerve)
  3. Postero - superior wall: Facial nerve. The fibres of facial nerve come here through the Arnold’s nerve.
  1. Tympanic Membrane
    Pearly white elliptical membrane
    1. Is positioned at angle of 55° to the floor; 40-50° angles with the anterior wall.
      This angle is attained at 4-5 yrs age.
    2. Layers:
      1. Epidermis: (Ectoderm) Is the outer layer and is continuous with the skin of the canal
      2. Fibrous layer: (Mesoderm) collagen fibres
        1. Radial
        2. Circular
        3. Parabolic and transverse
      3. Mucosal layer (Endoderm)
    3. ​​Two parts
      Pars Tensa and Pars flaccida (shrapnel’s membrane)

Extra Edge.

  1. Area of adult tympanic membrane is 90 mm2, of which only 55 mm2 is functional. Area of stapes footplate is 3.2 mm2. Area ratio (or hydraulic ratio) is 17:1. According to other workers, functional area is 45 mm2 and area ratio 14: 1.
  2. Tympanic membrane develops from all the three germinal layers: ectoderm (outer epithelial layer) mesoderm (middle fibrous layer) and endoderm (inner mucosal layer).


MCQ. Prussak’s space lies medial to pars flaccida, lateral to the neck of malleus and above the lateral process of malleus. Anteriorly, posteriorly and superiorly, it is bounded by lateral malleal ligament. Posteriorly, it also has a gap through which the space communicates with epitympanum
Anterior fouch of von troeltsenbetween tympanic membrane and ant. malleolar fold
Posterior pouch of
Von troeltsen between tympanic membrane and posterior malleolar fold

  1. Middle Ear:​
  1. Posterior wall:
    1. Aditus
    2. Antrum
    3. Facial nerve (vertical part)
    4. Facial recess area
  2. Anterior wall: Above to down:
    Four openings:
    1. Canal for Tensor tympani
    2. Eustachian tube
    3. Petrotympanic
    4. Opening for Chorda tympani
  3. Medial wall:
    1. Inner ear
    2. Cochlea
    3. Vestibule
    4. Lateral/superior semicircular Canal
    5. Canal
    6. Sinus tympani
  4. Lateral wall:
    1. Tympanic membrane
    2. Bony outer attic wall (Scutum)
  5. Roof: Middle cranial fossa (Tegmen tympani)
  6. Floor: Jugular bulb​
Contents of Middle Ear:
  1. Air
  2. 3 ossicles( malleus, incus, stapes)
  3. 2 muscles (stapedius, Tensor tympani)
  4. Nerves (Chorda tympani, tympanic plexus)

Middle Ear:

  1. Parts:
    1. Epitympanum: Medial to the Shrapnell’s membrane
    2. Mesotympanum: Medial to the pars tensa
    3. Hypotympanum: Below the level of pars tensa
  2. Dimensions: Vertical Diameter: = 15mm
  3. Transverse diameters:
    6 mm : Epitympanum
    4 mm : Hypotympanum
  4. Middle ear cleft: Middle ear + aditus + antrum+ mastoid air cells + Eustachian tube area.
  5. Mucosal lining:
    1. Anterior and inferior wall: ciliated columnar epithelium with goblet cells
    2. Floor: Cuboidal cells with loss of cilia
    3. Attic and antrum: pavement cells

MCQ: 2 mm: Opposite umbo, Hence is the narrowest part of the middle Ear.

Extra Edge: Middle Ear Cleft: Tympanic cavity (middle ear) + Eustachian tube + aditus + mastoid antrum + air cell system. 

MCQ. Mastoid antrum lies 12-15 mm deep from the surface of suprameatal triangle in an adult. The thickness of the bone overlying the antrum is only 2 mm at birth and then increases at the rate of 1 mm per year.
Tegmen mastoideum is the name given to the bone that covers the antrum on its lateral side.
MCQ. Mastoid tip does not develop till 2 years; hence postaural incision to open the mastoid before this age needs to be modified to avoid injury to the facial nerve.
MCQ. Solid angle is the area where three bony semicircular canals meet.
MCQ: Korner’s septum: is persisting petro - squamous suture line.

MCQ. Vertical and anteroposterior dimensions of middle ear are 15 mm each while transverse dimension is 2 mm at mesotympanum, 6 mm above at the epitympanum and 4 mm below in the hypotympanum. Thus, middle ear is the narrowest between the umbo and promontory.

MCQ. Eustachian tube is 36 mm long, one-third is bony and two thirds cartilaginous. Normally, it remains
closed. Opening of the tube is an active process due to contraction of Tensor veli palatini muscle while closure is
passive due to recoil of the cartilage. 
MCQ. Frenzel manoeuvre. It is used to open the eustachian tube and ventilate the middle ear by contracting
muscles of the floor of mouth and pharynx while nose, mouth and glottis are closed. It is a little more difficult to
learn than Valsalva manoeuvre. 
MCQ. Patients with cleft palate have eustachian tube dysfunction and develop persistent otitis media with effusion and recurrent acute otitis media.

Mastoid Antrum:

  1. Anterior wall: Aditus to antrum,: Lateral semicircular canal
  2. Posterior wall: Sigmoid sinus
  3. Roof: Tegmen antri
  4. Medial wall: Posterior semicircular canal
  5. Lateral wall: Bony plate
    1. 2mm in thickness: At birth
    2. Grows at the rate of 1 mm / year)
    3. Final thickness in adults: 12-15 mm)
      This the thickness one has to

      negotiate during mastoidectomy.
Deep to McEwen’s Triangle,
Suprameatal angle: bounded by
Suprameatal crest (superiorly), P-Sup canal wall (anteromedially), tangent to post canal wall posteriorly


Fig. MacEwen’s (suprameatal) triangle. It is bounded by temporal line (a), dashed posterosuperior segment of  bony external auditory canal (b) and The line drawn tangent to the external canal (c). It is an important landmark to locate the mastoid antrum in mastoid surgery.

P.S: Korner's Septum (Wall of Schwartze and eye shell)
  1. Is a bony plate separating the superficial squamosal cells from the deep petrosal cells
  2. Is a persistent petrosquamosal suture-
  3. It has significance during surgery of mastoid. (Difficulty identification of antrum) 

Types of mastoid cavities:

  1. Cellular/pneumatic (80%)
  2. Diploic/small celled
  3. Acellular/sclerotic

Eustachian Tube:

  1. Direction: Upwards, outwards and backwards
  2. Length: 36mm l 2 mm : Bony (Proximal)
    24 mm : Fibrocartilaginous
  3. Pharyngeal opening: 1-1.25 cm behind and little below the posterior end of the inferior turbinate --> This is land mark of Eusta chain tube.
  4. Tympanic plexus:
    1. Formed by
    • Tympanic branch of IX nerve
    • Caroticotympanic nerves from the sympathetic plexus

Tests for ET

  1. Valsalva
  2. Frenzel
  3. Seglisation
  4. Politzerization
  5. ET cannulation
  6. Tympanometry
  7. Sonotubometry
  8. Radiological
  1. Inner Ear:​
2 parts (bony labyrinth and membranous labyrinth)
  1. Bony labyrinth
    1. Cochlea
    2. Vestibule​
      Fissula (ante fenestrum)
      Fossula (post fenestrum)
      Semicircular ducts
  2. Membranous labyrinth:
    Cochlear ducts  3 semicircular ducts
    Saccule endolymphatic duct and sac
  1. Bony Labyrinth


  1. Has approx. two and one half turns
  2. Coils turn about a central cone called Modiolus
  3. Modiolus: Arises from the cochlear nerve portion of the fundus of the internal auditory canal
  4. Arising from the modiolus is a mm shelf of bone which spirals upwards within the lumen of the
  5. cochlea as the bony Spiral Lamina.
  6. To this Spiral Lamina is attached the membranous spiral lamina which divides each coil into scala vestibule and Scale tympani
  7. Helicotrema: Communication on each side of the spiral lamina between the two perilymphatic
  8. Spaces (scala vestibuli and scala tympani)
  9. Site: at the apex of the cochlea
  10. Base of the cochlea
  11. Scala vestibule: Opens into the vestibule
  12. Scala tympani: ends blindly
  13. Floor has the fenestra cochlea, which is covered by the round window membrane.
  14. Cochlear aqueduct: Communication with the subarachnoid space of the posterior cranial fossa.

MCQ. In Fitzgerald-Hallpike (bithermal caloric) test, thermal stimulation occurs in the horizontal semicircular
canal Cold water (30°C) causes nystagmus to the opposite side while warm water (44°C) to the same side.
Remember COWS (Cold-Opposite- Warm-Same).

Extra Edge. Modiolus is the central bony axis of cochlea and measures 5 mm in length.

  1. Vestibule:
    1. Central portion of the bony labyrinth
    2. Anterior wall: has the opening of scala vestibuli
    3. Posterior wall: has the “5” opening of the semicircular canals.
  1. ​​Part of Semicircular canals: Horizontal/lateral, superior, posterior
    1. Ampulla:
      One end of each canal dilates 10 form the Ampulla which contains the vestibular sensory epithelium
    2. Crus commune:
      Formed by the non-ampullated ends of the superior and posterior semicircular canal
    3. Arcuate eminence:
      Bulge on the roof due to superior semicircular canal.
  1. ​​Membranous Inner Ear:
    1. Cochlear duct: (scala media)
      1. Basilar membrane, supports the organ of Corti
      2. Reissner’s membrane: separates it from the scala vestibuli Stria vascularis
      3. Cochlear duct is connected to the saccule by ductus reuniens
      4. Hair cells: Inner -3,500 (afferent primarily); outer- 12000 (more sensitive to damage; efferent primarily)
      5. Space of Nuel: between inner hair cells

i. Basal coil of the cochlear   :   High Frequency Sounds
ii. Apex Of The Cochlear        :   Low Frequency Sounds

  1. Utricle and Saccule:
    1. The two are connected by utriculosaccular duct
    2. Sensory epithelium: macula
    3. Responds to linear acceleration and deceleration
    4. Sensory epithelium contain otoconia
  2. Inner Ear Fluids- Endolymph. Perilymph, Cortilymph




Endolymph Perilymph
A. Production From C.S.F fluid through the cochlear aqueduct, loose connective tissue around the cochlear nerve at the internal auditory meatus
Stria vascularis From stria vascularis adjacent to scala vestibuli
Planum semilunatum  
Dark vestibular cells  

B. Table: Composition of inner ear fluids
  Endolymph Perilymph CSF
Na+ (mEq/L) 5 140 152
K+ (mEq/L) 144 10 4
Protein (mg/dL) 126 200-400 20-50
Glucose 10-40 85 70


Extra Edge

Hennebert’s phenomenon. Dysequilibrium following nose blowing or lifting a heavy object. Seen in perilymph fistula (do not confuse with Hennebert’s sign).


Blood supply to the labyrinth:

Labyrinth artery (Branch of) anterior inferior cerebellar artery (AICA)

(which is a branch of basilar artery)

Some time the labyrinth artery arises directly from basilar artery.

Fig: Blood supply of labyrinth: 

 Internal Auditory Meatus:
  1. Length= 1 cm
  2. Vertical dia= 2-8 mm (difference b/w the “2” sides should not be more than 1 mm) (on radiological investigation ) If the difference is more than 2 mm, it is sign of acoustic neuroma.
  3. Av. length of the posterior wall= 8mm (difference should not be> 2 mm)

Physiology of Hearing
Intensity of sounds at a distance of 1 m Audible range- 16-20,000Hz; Threshold for N hearing - OdB

  1. 1.Whisper                          =  30dB
  2. 2.Normal conversation        =  60dB
  3. 3.Shout                             =  90dB
  4. 4.Discomfort                      =  120dB
  5. 5.Painful                           = 130dB

Extra Edge

  1. Cochlea is a coiled tube making 2.5 to 2.75 turns. When straightened it measures 32 mm.
  2. Donaldson’s line passes through horizontal canal and bisects the posterior canal. It is landmark for   endolymphatic sac which lies anterior and inferior to it
  3. Endolymph is produced by cells of stria vascularis of the cochlea and dark cells of the vestibular labyrinth.  It is absorbed by endolymphatic sac.


Fig: Auditory pathways from the right cochlea. Note bilateral route through brainstem and bilateral cortical representation.

Peripheral Receptor Auditory Pathway

  1. Organ of Corti
    1. Sensory hair cells- Gives rise to auto acoustic emissions, With age hair cells at base are more than at the apex
    2. Two types of Sensory hair cells– Inner and Outer
      Primarily afferent

      Susceptible to ototoxic drugs and noise
  2. Supporting cells
    1. Pillar cells
    2. Dieters cells
    3. Hensen’s cells

Table: Differences between inner and outer hair cells:


Inner hair cells

Outer hair cells

Total no.




One row

Three or four rows




Nerve supply

Primarily afferent fibres afferent

Mainly efferent fibres and very few defferent


Develop earlier

Develop late


Transmit auditory stimuli

Modulate function of inner hair cells


More resistant

Easily damaged by ototoxic drugs and
high intensity noise

  1. Peripheral receptors of the vestibular system
    1. Cristae: à Angular acceleration
    2. Deviation of the kinocilium towards the stereocilia: Depolarization of the afferent neurons
    3. Gelatinous layer of crista: Cupula
    4. Macula: Linear acceleration & deceleration
    5. Gelatinous layer of the macula: Otolithic membrane
Table: Ototoxic drugs

A. Aminoglycoside antibiotics

             ·    Streptomycin          · Gentamicin             ·   Tobramycin          · Neomycin

             ·    Kanamycin             · Amikacin                 ·   Sisomicin     

B. Diuretics

             ·    Furosemide            · Ethacrynic acid

C. Antimalarials

             ·    Quinine                  · Chloroquine

D. Cytotoxic drugs

             ·    Nitrogen mustard    · Cisplatin

             ·    Carboplatin

E. Analgesics

             ·    Salicylates              · Indomethacin

             ·    Phenylbutazone      · Ibuprofen

F. Chemicals

             ·     Alcohol                  · Tobacco

             ·    Marijuana               · Carbon monoxide poisoning

G. Miscellaneous

             ·    Erythromycin          · Ampicillin

             ·    Propranolol             · Propyl thiouracil

Test Your Skills Now!
Take a Quiz now
Reviewer Name