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Embryology of the Human Ear. Ashley Balaker, M.D. March 17, 2010. Outline. Inner Ear Middle Ear External Ear. Inner Ear. Ectoderm = membranous labyrinth Mesoderm = bony labyrinth 3rd week Surface ectoderm = otic placode Invaginates --> otic pit 4th week

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embryology of the human ear

Embryology of the Human Ear

Ashley Balaker, M.D.

March 17, 2010

outline
Outline
  • Inner Ear
  • Middle Ear
  • External Ear
inner ear
Inner Ear
  • Ectoderm = membranous labyrinth
  • Mesoderm = bony labyrinth
  • 3rd week
  • Surface ectoderm = otic placode
  • Invaginates --> otic pit
  • 4th week
  • Pit edges fuse to become otocyst
inner ear4
Inner Ear
  • Dorsal utricular portion, ventral saccular portion
  • Utricular portion
    • 3 diverticula for semicircular canals
  • Saccular portion
    • Tubular diverticulum (cochlear duct) grows in spiral fashion to become membranous cochlea
    • The organ of Corti differentiates from cells along the wall of the cochlear duct.
inner ear5
Inner Ear
  • 6th week
  • neuroectoderm --> spinal and vestibular ganglia and corresponding sensory nerves
  • Mesoderm around otocyst soon forms a cartilaginous otic capsule.
  • Ossifies by 25 weeks
inner ear6
Inner Ear
  • Vacuoles containing the perilymph develop within the otic capsule.
  • The vacuoles enlarge and unite to form the perilymphatic space
  • Divides into the scala tympani and the scala vestibuli.
  • The cartilaginous otic capsule ossifies to form the bonylabyrinth of the inner ear (mesoderm).
middle ear
Middle Ear
  • 1st pharyngeal pouch endoderm
    • Lining of middle ear (tympanic cavity)
    • Connection to pharynx elongates and forms eustachian tube
middle ear8
Middle Ear
  • 1st and 2nd pharyngeal arch cartilage (mesoderm) --> ossicles
  • 1st (Meckel’s): epitypanum ossicles
    • Head of malleus, body and short process of incus
  • 2nd (Reichert’s): mesotympanum ossicles
    • Long process malleus, long process incus, stapes superstructure
  • Stapes footplate: otic capsule
middle ear9
Middle Ear
  • Ossicles full sized by 15 weeks
  • Ossify by 25 weeks
external ear
External Ear
  • EAC develops from the surface ectoderm that covers the dorsal end of the first pharyngeal grove.
  • A solid epithelial plate meatal plug develops at the bottom of the funnel-shaped pharyngeal groove.
external ear12
External Ear
  • TM
    • Inner layer endoderm
    • Middle layer mesoderm
    • Outer layer ectoderm
auricle
Auricle
  • 6 Hillocks of His (mesoderm)
  • 1st pharyngeal arch
    • 1: Tragus
    • 2: Helical crus
    • 3: Helix
  • 2nd pharyngeal arch
    • 4: antihelix
    • 5: antihelix
    • 6: antitragus