clinical anatomy & physiology of the ear yang jun, md, ph.d. 09/18/09
TRANSCRIPT
Clinical anatomy & physiology of the ear
YANG Jun, MD, Ph.D.
09/18/09
Otology & neurotologySurgical management on hearing loss
Conductive hearing loss: tympanoplasty, ossicular chain 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 spasmSurgical management on vertigoTrigeminal neuralgiaRepaire of CSF leakage
Temporal boneLocation : lateral skullNeighbour : parietal bone, sphenoid bone, occipital boneComposition: squamous part, tympanic part, pars
mastoidea, petrosal part
Anatomy of the external earauricle
anterior notch of ear-an incision can be made less subcutaneous tissue
difficult absorption of hematoma prone to cold injury
Anatomy of the auricle
Anatomy of the external earexternal auditory canal
2.5-3.5cm2.5-3.5cm outerouter1/31/3 :: cartilage innerinner2/32/3 :: bonebone Stenosis: juncture of bone and cartilage, bony part (0.5cm
from the tympanic anulus)
Anatomy of the middle ear
Tympanic cavityEustachian tubeTympanic sinusMastoid cavity
Tympanic cavity
Attic, mesotympanum, hypotympanum Six walls: interior, exterior, anterior, posterior,
superior, inferior
Tympanic cavity
颈静脉球颈静脉球
颈内动脉颈内动脉蜗窗小窝蜗窗小窝
鼓膜鼓膜鼓索神经鼓索神经
砧骨砧骨锤骨锤骨
鼓膜张肌鼓膜张肌附着处附着处 咽鼓管鼓口咽鼓管鼓口
鼓膜张肌鼓膜张肌半管半管
鼓岬鼓岬大脑颞叶大脑颞叶
匙突匙突
鼓索神经孔鼓索神经孔面神经面神经锥隆起锥隆起鼓窦入口鼓窦入口外半规管凸外半规管凸面神经管凸面神经管凸 镫骨底板镫骨底板
Exterior wall-tympanic membraneTympanic membrane
Semi-transparent film, 1cm2, 1mmUpper is pars flaccid, lower is pars tensaThree layer construction: epithelial lamina, fibrous
lamina, mucous layer
tympanic membrane
Interior wallNamely exterior wall of the inner earCenter-promontorium tympaniPost-superior : vestibular window-vestibulePost-inferior : cochlear window-scala tympani horizontal part of facial nerve canalprominence of lateral semicircular canalcochleariform process
Anterior wall
Namely carotid wallInferior part is separated with
the carotid arteryTwo openings at the superior
part: semicanal for tensor tympani (upper), semicanal for auditory tube (lower)
Posterior wallMinipore at the posterior wall-
aditus ad antrum tympanicumincudal fossa- juncture of
horizontal part and perpendicular part
pyramidal eminence-about at height of vestibular window
facial recess-posterior tympanotomy
Superior wallNamely tegmen tympaniBe 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 wallNamely jugular wallBe separated with the
jugular bulbblue drum
Content in the tympanic cavityossicles ( smallest bone in the human body ) :
malleus, incus, stapes- ossicular chainligamenta ossiculorum auditus: ligament of the
malleus, incus and stapesmuscle in the tympanic cavity: tensor tympani muscle,
stapedial musclechorda tympani nerve
Ossicular chain
Eustachian tubePassageway between tympanic
cavity and nasopharynx, outer 1/3-bony 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 cavityTympanic sinus: pneumatic space and passage between
the attic and mastoid cavityMastoid 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 labyrinthPerilymph is full of the space between bony labyrinth
and membranous labyrinth, endolymph is full of the membranous labyrinth
bony labyrinth
Compact boneVestibule, semicircular canal,
cochlea
VestibuleBetween the cochlea and the semicircular canalFive openings from three bony semicircular canalssaccular recess, utricular recessExterior wall- vestibular window: sealed by footplate
of the stapes
Bony semicircular canalsThree 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 labyrinthComposed of membranous duct and membranous sacfixation at bony labyrinth by fiber bundledividing into utricle, saccule, membranous semicircular
canal and membranous cochlea (scala media)cross-connection each other
Membranous labyrinth Utricle
Utricular recessMacula utriculi-sense of balanceFive openings in the posterior wall connect with three
semicircular canalsConnection 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 labyrinthSaccule
Saccular recessMacula sacculi-sense of balanceConnection with utriculosaccular duct and endolymphatic duct
Membranous labyrinthMembranous semicircular canal Connection with the utricle
Membranous labyrinthMembranous 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 laminaOrgan of Corti : hearing receptor composed of outer hair cells
and inner hair cells
Physiology of the earHearing Balance
Route of sound conductingAir conduction
Sound wave auricle external auditory canal
vestibular window perilymph/endolymph organ of
Corti auditory nerve nucleus auditory cortex
Route of sound conductingBone conduction
Sound wave makes the perilymph vibrate through skull route, then stimulates the organ of Corti by which hearing generate. Translatory mode of bone conduction Compressional mode of bone conduction
Physiological functions of the external ear
Gathering sound Discriminating direction ResonanceProtectionSound wave pressurizing
Physiological functions of the middle ear
Transformation and gainStructure 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 1.3:1
1.3×17=22.1 27dB
Function of Middle ear—pressure amplification-Function of Middle ear—pressure amplification-ossiclesossicles
Energy loss at air-fluid interface-99.9% loss (-30 dB)Energy loss at air-fluid interface-99.9% loss (-30 dB)
•Malleus longer than incus-amplify pressure ~1.7X (+2 Malleus longer than incus-amplify pressure ~1.7X (+2 dB)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 DrainagePrevention of retrograde infectionNoise abatement
Auditory physiology
TransmissionSensation
Basilar membrane displacement for a 1 kHz tone
Basilar membrane displacement for a 250 Hz tone
Basilar membrane displacement for a 4 kHz tone
Cochlear mechanical response due mass and stiffness Cochlear mechanical response due mass and stiffness gradientgradient
•Mass & stiffness gradient gives rise to a so-called “traveling Mass & stiffness gradient gives rise to a so-called “traveling wave”wave”
•Characteristic frequency—frequency which produces the Characteristic frequency—frequency which produces the largest amplitude of responselargest amplitude of response
•Apex-maximum response to low frequenciesApex-maximum response to low frequencies
•Base maximum response to high frequenciesBase maximum response to high frequencies
Mass-increases from base (stapes) to apex
Stiffness-increases from apex to base
1
23
4
Envelope of traveling wave
Characteristic frequency
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: 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”
Model of organ of Corti Responds to OHC Electromotility
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