Development of the Ear

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Development of the Ear
Jittipan Chavadej, Ph.D.
Anatomy Dept., Fac. of Science Mahidol University
yr.,2000
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Mature components of the ears
The ear is composed of inner, middle and outer
ear portions

• outer ear -auricle
• -ext. auditory meatus
• -tympanic membrane

• middle ear - malleus, incus stapes
• - auditory tube

• inner ear - cochlear duct
• - semicircular canal

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Formation of the ear

• Dual origin
• - thickened ectodermal
• placode at rhombencephalon
• - first and second branchial
• arches

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Rhombencephalon regionformation of otic vesicles
Derivatives of the 1st 2nd branchial arches
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Development of inner ear
Induction - rhombencephalonsurface ectoderm
Otic placode Otic vesicle
Dorsal vestibular region
Ventral cochlear region
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Rhombencephalon regionotic placode , otic pit
and otic vesicle
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Membranous labyrinth
Ventral cochlear region
Saccule
Cochlear duct
Dorsal vestibular region
Utricle
Semicircular canals
Endolymphatic duct
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Development of the otic vesicle showing a dorsal
utricular portion with endolymphatic duct, and a
ventral saccular portion
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Saccule, cochlea organ of Corti
Outgrowth of cochlear duct-spiral fashion 8th
wk.- 21/2 turns
Cochlear duct conect with saccule through ductus
reuniens
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Cochlear duct mesenchyme
Cartilageous shell
Scala media
Scala tympani
Scala vestibuli
Basilar mem.
Vestibular mem.
(S.media S.vestibuli)
Organ of Corti
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Development of the scala tympani scala
vestibuli Notethe auditory nerve and spiral
ganglion
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Scala media - organ of Corti
Hair cells
Tectorial mem. (gelatineous substance)
Lateral wall-spiral ligament Medial - modiolus
- spiral ganglion
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Development of the organ of Corti
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Semicircular canals Utricle
Vestibular portion-central portion appose to
each other disappearance 3 semicircular
canals
Crus ampullare-crista ampullaris
UtricleSaccule-maculae acousticae
Statoacoustic ganglion CN VIII
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Development of the semicircular
canals Notedisappearance of the central portion
the ampullae in the semicircular canals
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Development of the Middle Ear

• Expansion of 1st pharyngeal pouch middle
  cavity auditory tube

Lining- endodermal origin

• 2nd mo.-blind end oftubotympanic tube 1st
  pharyngeal cleft

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Development of the middle ear Notetubotympanic
recess, mesenchymal condensation ear ossicle
formation
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6thwk.-condensation of mesenchyme (mesoderm)just
dorsal to the end of tubotympanic end ear
ossicles

• Tympanic cavity-ear ossicles in loose mesenchyme
  late pregnancy programmed cell death
  suspension of ear ossicles

• 2 mo. after birth-free movement of ear ossicles

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Development of the ear ossicles in the tympanic
cavity Note malleus contact with eardrum, stapes
contact with oval window and endodermal
epithelium of tympanic cavity
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• Dual origin of ear ossicles
• malleus incus-mesoderm of 1st branchial arch
• stapes-mesoderm of 2nd branchial arch

Tensor tympani mus.- CN V Stapedius - CN VII
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Development of the External Ear
Pinna - mesenchyme of 1st 2nd branchial
arches2nd mo. auricular hillock
enlargement(asymmetry)
External auditory meatus - inward expansion of
the 1st branchial cleft
3rd-meatal plug(solid epith. plate) 7th-dissolutio
n of meatal plug
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Lateral view of the head showing the six
auricular hillocks surrounding the dorsal end of
the 1st pharyngeal cleft
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Congenital malformation of the ear

• Congenital deafness-inner ear deafness(rubella),mi
  ddle ear deafness (1st 2nd arches),agenesis of
  external ear

• Auricular anomalies

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THE END