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Clinical anatomy & physiology
of the ear
YANG Jun, MD, Ph.D.
09/18/09
Otology & neurotology
 Surgical management on hearing loss
 Conductive hearing loss: tympanoplasty, ossicular chain
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reconstruction, stapes surgery
 Sensorineural hearing loss : implantable hearing-aids,
cochlear implatation
Tumor in the lateral skull base,such as acoustic neuroma
Facial nerve: facial paralysis, facial spasm
Surgical management on vertigo
Trigeminal neuralgia
Repaire of CSF leakage
 Temporal bone
 Location : lateral skull
 Neighbour : parietal bone, sphenoid bone, occipital bone
 Composition: squamous part, tympanic part, pars mastoidea,
petrosal part
Anatomy of the external ear
 auricle
 anterior notch of ear-an incision can be made
 less subcutaneous tissue
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difficult absorption of hematoma
prone to cold injury
Anatomy of the auricle
Anatomy of the external ear
 external auditory canal
2.5-3.5cm
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outer1/3：cartilage
inner2/3：bone
Stenosis: juncture of bone and cartilage, bony part (0.5cm from the
tympanic anulus)
Anatomy of the middle ear
 Tympanic cavity
 Eustachian tube
 Tympanic sinus
 Mastoid cavity
Tympanic cavity
 Attic, mesotympanum, hypotympanum
 Six walls: interior, exterior, anterior, posterior, superior, inferior
Tympanic cavity
面神经管凸 镫骨底板
外半规管凸
匙突
鼓窦入口
大脑颞叶
锥隆起
鼓索神经孔
鼓岬
面神经
砧骨
锤骨
鼓膜张肌
鼓膜张肌
半管
附着处
咽鼓管鼓口
鼓索神经
鼓膜
颈内动脉
蜗窗小窝
颈静脉球
Exterior wall-tympanic membrane
 Tympanic membrane
 Semi-transparent film, 1cm2, 1mm
 Upper is pars flaccid, lower is pars tensa
 Three layer construction: epithelial lamina, fibrous lamina,
mucous layer
tympanic membrane
Interior wall
 Namely exterior wall of the inner ear
 Center-promontorium tympani
 Post-superior : vestibular window-vestibule
 Post-inferior : cochlear window-scala tympani
 horizontal part of facial nerve canal
 prominence of lateral semicircular canal
 cochleariform process
Anterior wall
 Namely carotid wall
 Inferior part is separated with the
carotid artery
 Two openings at the superior part:
semicanal for tensor tympani (upper),
semicanal for auditory tube (lower)
Posterior wall
 Minipore at the posterior wall- aditus
ad antrum tympanicum
 incudal fossa- juncture of horizontal
part and perpendicular part
 pyramidal eminence-about at height
of vestibular window
 facial recess-posterior tympanotomy
Superior wall
 Namely tegmen tympani
 Be separated with the temporal lobe of
the cerebrum in the middle fossa
 The petrosquamous fissure in infant is
not closed-one of the route by which
infection from the middle ear could get
into
Inferior wall
 Namely jugular wall
 Be separated with the
jugular bulb
 blue drum
Content in the tympanic cavity
 ossicles（smallest bone in the human body）: malleus, incus,
stapes- ossicular chain
 ligamenta ossiculorum auditus: ligament of the malleus, incus
and stapes
 muscle in the tympanic cavity: tensor tympani muscle, stapedial
muscle
 chorda tympani nerve
Ossicular chain
Eustachian tube
 Passageway
between tympanic
cavity and nasopharynx, outer 1/3bony part, inner 2/3- cartilaginous
part. Isthmic portion-junction of
bony part and cartilaginous part.
 The opening at the nasopharynx
is open when muscle contraction
in order to adjust air pressure in
the tympanic cavity.
 Infection is prone to enter the
tympanic cavity because of
Horizontal, short and wide
Eustachian tube in child.
Tympanic sinus and mastoid cavity
 Tympanic sinus: pneumatic space and passage between the attic and
mastoid cavity
 Mastoid cavity: cells in the temporal bone-pneumatic type, diploetic
type, constrictive type and mixed type
CT scan of temporal bone
Anatomy of the inner ear
 Also labyrinth, containing apparatus responsible for hearing and
balance
 The inner ear is divided into bony labyrinth and membranous
labyrinth
 Perilymph is full of the space between bony labyrinth and
membranous labyrinth, endolymph is full of the membranous
labyrinth
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bony labyrinth
 Compact bone
 Vestibule, semicircular canal, cochlea
Vestibule
 Between the cochlea and the semicircular canal
 Five openings from three bony semicircular canals
 saccular recess, utricular recess
 Exterior wall- vestibular window: sealed by footplate of the
stapes
Bony semicircular canals
 Three curved bony ducts that form right angle mutually-
lateral, superior and posterior semicircular canal
 A common crus is formed by the superior and posterior
semicircular canal, therefore, five openings from three
semicircular canals enter the vestibule
Membranous labyrinth
 Composed of membranous duct and membranous sac
 fixation at bony labyrinth by fiber bundle
 dividing into utricle, saccule, membranous semicircular canal and
membranous cochlea (scala media)
 cross-connection each other
Membranous labyrinth
 Utricle
 Utricular recess
 Macula utriculi-sense of balance
 Five openings in the posterior wall connect with three semicircular canals
 Connection with the utriculosaccular duct and endolymphatic duct in the
anterior wall. Vestibular aqueduct. Endolymphytic sac (within dura behind
the petrosal part of the temporal bone)
Membranous labyrinth
 Saccule
 Saccular recess
 Macula sacculi-sense of balance
 Connection with utriculosaccular duct and endolymphatic duct
Membranous labyrinth
 Membranous semicircular canal
Connection with the utricle
Membranous labyrinth
 Membranous cochlea (scala media)
 Between the osseous spiral lamina and the lateral wall of the osseous
cochlear canal, also between scala vestibuli and scala tympani, containing
endolymph
 Basilar membrane: from free edge of the osseous spiral lamina
 Organ of Corti : hearing receptor composed of outer hair cells and inner hair
cells
Physiology of the ear
 Hearing
 Balance
Route of sound conducting
 Air conduction
Sound wave auricle external auditory canal vestibular
window perilymph/endolymph organ of Corti auditory
nerve nucleus auditory cortex
Route of sound conducting
 Bone conduction
 Sound wave makes the perilymph vibrate through skull route, then
stimulates the organ of Corti by which hearing generate.
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Translatory mode of bone conduction
Compressional mode of bone conduction
Physiological functions of the external ear
 Gathering sound
 Discriminating direction
 Resonance
 Protection
 Sound wave pressurizing
Physiological functions of the middle ear
 Transformation and gain
 Structure for sound transmission and transformation: tympanic
membrane and ossicular chain
Physiological functions of the tympanic membrane
 Valid area of vibration : 55 mm2
 Area of the footplate: 3.2 mm2
17times
Function Middle ear—amplification from area ratio
•Pressure = Force/area
•Area of tympanic membrane ~17 > area stapes
•Gain of area ratio ~24 dB
Physiological functions of the ossicular chain
 Lever
manubrium of malleus
long crus of incus
 1.3×17=22.1
27dB
1.3:1
Function of Middle ear—pressure amplification-ossicles
Energy loss at air-fluid interface-99.9% loss (-30 dB)
•Malleus longer than incus-amplify pressure ~1.7X (+2 dB)
Physiological functions of muscles in the tympanic cavity
 stapedial muscle: decreasing pressure of perilymph
Physiological functions of muscles in the Eustachian tube
 Keeping balance of pressure in the middle ear
 Drainage
 Prevention of retrograde infection
 Noise abatement
Auditory physiology
 Transmission
 Sensation
Basilar membrane displacement for a 250 Hz tone
Basilar membrane displacement for a 1 kHz tone
Basilar membrane displacement for a 4 kHz tone
Cochlear mechanical response due mass and stiffness gradient
•Mass & stiffness gradient gives rise to a so-called “traveling wave”
•Characteristic frequency—frequency which produces the largest
amplitude of response
•Apex-maximum response to low frequencies
•Base maximum response to high frequencies
Envelope of
traveling wave
Characteristic frequency
1
2
3
4
Mass-increases from base (stapes) to apex
Stiffness-increases from apex to base
Stereocilia on OHCs
attached to tectorial
membrane
Stereocilia on IHCs free
standing
Motion of basilar membrane
towards scala vestibuli
deflects stereocilia in
excitatory direction
Tectorial membrane
deflects OHC stereocilia
Viscous fluid drag of fluid
deflects IHC stereocilia
Model of organ of Corti Responds to OHC Electromotility
•Model: OHC contraction cause
organ of Corti to distort as shown
herer
•Cell motility feeds back
enhancing basilar membrane
motion thereby increasing
traveling wave amplitude and
making the “cochlea active”
OHC contracts in-phase with deflection of the hair bundle toward the tallest stereocilia.
The current through the cell increases with deflection in this direction. If the current is
modulated slowly (compared to 1 kHz), then the voltage across the lateral membrane will
be in-phase with the current. Conformational changes in many voltage sensitive molecules
situated within the lateral membrane cause the length of the cell to change. The diameter
of the cell increases slightly as the cell contracts to maintain constant cell volume.
Balance physiology
 Semicircular canal： Perception of positive or negative angular
acceleration
 Saccule and utricle : Perception of linear acceleration
 Macula sacculi: Perception of static balancing and linear
acceleration on the coronal plane
 Macula utriculi: Perception of static balancing and linear
acceleration on the vertical plane