Clinical anatomy

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• Clinical anatomy physiology of the ear
• YANG
  Jun, MD, Ph.D.
• 
  09/18/09

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Otology neurotology

• Surgical 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 spasm
• Surgical management on vertigo
• Trigeminal neuralgia
• Repaire of CSF leakage

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• Temporal bone
• Location  lateral skull
• Neighbour  parietal bone, sphenoid bone,
  occipital bone
• Composition squamous part, tympanic part, pars
  mastoidea, petrosal part

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Anatomy of the external ear

• auricle
• anterior notch of ear-an incision can be made
• less subcutaneous tissue
• difficult absorption of hematoma
• prone to cold injury

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Anatomy of the auricle
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Anatomy of the external ear

• external auditory canal
• 2.5-3.5cm
• outer1/3cartilage
• inner2/3bone
• Stenosis juncture of bone and cartilage, bony
  part (0.5cm from the tympanic anulus)

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Anatomy of the middle ear

• Tympanic cavity
• Eustachian tube
• Tympanic sinus
• Mastoid cavity

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Tympanic cavity

• Attic, mesotympanum, hypotympanum
• Six walls interior, exterior, anterior,
  posterior, superior, inferior

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Tympanic cavity
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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

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tympanic membrane
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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

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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)

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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

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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

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Inferior wall

• Namely jugular wall
• Be separated with the jugular bulb
• blue drum

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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

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Ossicular chain
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Eustachian tube

• Passageway 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.

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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

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CT scan of temporal bone
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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

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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

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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

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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

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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)

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Membranous labyrinth

• Saccule
• Saccular recess
• Macula sacculi-sense of balance
• Connection with utriculosaccular duct and
  endolymphatic duct

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Membranous labyrinth

• Membranous semicircular canal
• Connection with the utricle

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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

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Physiology of the ear

• Hearing
• Balance

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Route of sound conducting

• Air conduction
• Sound wave auricle external auditory
  canal vestibular window perilymph/endolymph
  organ of Corti auditory nerve nucleus
  auditory cortex

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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.
• Translatory mode of bone conduction
• Compressional mode of bone conduction

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Physiological functions of the external ear

• Gathering sound
• Discriminating direction
• Resonance
• Protection
• Sound wave pressurizing

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Physiological functions of the middle ear

• Transformation and gain
• Structure for sound transmission and
  transformation tympanic membrane and ossicular
  chain

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Physiological functions of the tympanic membrane

• Valid area of vibration  55 mm2
• Area of the footplate 3.2 mm2
  17times

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Physiological functions of the ossicular chain

• Lever manubrium of malleus
• long crus of incus
  1.31
• 1.31722.1 27dB

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• Function of Middle earpressure
  amplification-ossicles
• Energy loss at air-fluid interface-99.9 loss
  (-30 dB)
• Malleus longer than incus-amplify pressure 1.7X
  (2 dB)

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Physiological functions of muscles in the
tympanic cavity

• stapedial muscle decreasing pressure of perilymph

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Physiological functions of muscles in the
Eustachian tube

• Keeping balance of pressure in the middle ear
• Drainage
• Prevention of retrograde infection
• Noise abatement

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Auditory physiology

• Transmission
• Sensation

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Basilar membrane displacement for a 250 Hz tone
Basilar membrane displacement for a 1 kHz tone
Basilar membrane displacement for a 4 kHz tone
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Model of organ of Corti Responds to OHC
Electromotility
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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.
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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