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Jittipan Chavadej, Ph.D. Anatomy Dept., Fac. of Science Ma
hidol Universityyr.,2000
Mature components of the earsThe 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• i nner ear - cochlear duct - semicircular canal
Formation of the ear Dual origin
- thickened ectodermal
placode at rhombencephalon
- first and second branchial
arches
Rhombencephal on region:formati on of otic vesicle
s
Derivatives of th e 1st 2& nd branc
hial arches
Development of inner ear - Induction rhombencephalon~surfa
ce ectoderm
Otic placode Otic vesicle
Dorsal vestibular region
Ventral cochlear region
Rhombencephalon region:otic placode
, otic pit and otic vesicle
Ventral cochlear region
Saccule
Cochlear duct
Dorsal vestibular region
Utricle Semicircular
canals
Endolymphatic
duct
Membranous labyrinth
Development of the otic vesicle showing a dorsal utric ular portion with endolymphatic duct, and a ventral sa
ccular portion
Saccule, cochlea & organ of CortiOutgrowth of cochlear duct-spiral fashion 8th wk.- 21/2
turns Cochlear duct conect with saccu
le through ductus reuniens
Cochlear duct + mesenchyme
Scala media
Cartilageous shell
Scala vestibuli
Scala tympani
Vestibular mem. Basilar mem.
Organ of Corti (S.media & S.vestibuli
)
Development of the scala tympani & scala vestibuli
Note:the auditory nerve and spiral ganglion
Scala media - organ of Corti
Hair cells
Tectorial mem . (gelatineous substanc
e) - Lateral wall spiral ligament
- Medial modiolus
- spiral ganglion
Development of the organ of Corti
Semicircular canals & Utricle - Vestibular portion central portion
appose to each other disappearance 3 semicircular canals - Crus ampullare crista ampullaris
- Utricle&Saccule maculae acousticae
Statoacoustic ganglion CN VIII
Development of the semicircular canals
Note:disappearance of the central portion & the ampull
ae in the semicircular canals
Development of the Middle EarExpansion of 1st pharyngeal pouch middle cavity & auditory tube
- * * Lining endodermal origin**
2nd - mo. blind end oftubotympan ic tube 1st pharyngeal cleft
Development of the middle ear
Note:tubotympanic recess, mesenchymal condensation
ear ossicle formation
6th -wk. condensation of mesench
yme (mesoderm):just dorsal to the end of tubo
tympanic end ear ossicles - Tympanic cavity ear ossicles in l
oose mesenchyme late pregnan cy: programmed cell death susp
ension of ear ossicles
- 2mo. after birth free moveme nt of ear ossicles
Development of the ear ossicles in the tympanic cavity
Note: malleus contact with eardrum, stapes contact wi th oval window and endodermal epithelium of tympani
c cavity
Dual origin of ear ossicles
• - malleus & incus mesoderm of 1st branchial arch
• - stapes mesoderm of 2nd branchia l arch
- *Tensor tympani mus. CN V
- *Stapedius CN VII
Development of the External Ear
Pinna - mesenchyme of 1st &2nd branchial arches:2nd mo. auricul
ar hillock enlargement(asymmetry)
External auditory meatus - inward expansion of the 1st branchial cleft
3rd- meatal plug (solid epith. plate)
7th- dissolution of meatal plug
Lateral view of the head showing the six auricular hillocks surrounding the dorsal end of the 1st pharyngeal cleft
Congenital malformation of the ear
•Congenital deafness-inner ear deafness(rubella),middle ear deafness (1st & 2nd
arches),agenesis of external ear
•Auricular anomalies