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Anatomy Dept., Fac. of Science Mahidol University
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 region:formation of otic vesicles
Derivatives of the 1st & 2nd branchial arches
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Development of inner ear
Induction - rhombencephalon~surface ectoderm Otic placode Otic vesicle Dorsal vestibular region Ventral cochlear region
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Rhombencephalon region:otic 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
Note:the 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 semicircular canals Crus ampullare-crista ampullaris Utricle&Saccule-maculae acousticae Statoacoustic ganglion CN VIII
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Development of the semicircular canals
Note:disappearance 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 st pharyngeal cleft
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Development of the middle ear
Note:tubotympanic 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 arches:2nd mo. auricular hillock enlargement(asymmetry) External auditory meatus - inward expansion of the 1st branchial cleft 3rd-meatal plug(solid epith. plate) 7th-dissolution 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),middle ear deafness (1st & 2nd arches),agenesis of external ear Auricular anomalies
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THE END
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