6th week intraembryonic life- 6 tubercles around 1st branchial cleft-they form the pinna by coalescing progressively-tragus develops from tubercle of 1st arch-rest of the pinna from 2nd arch
-faulty fusion between 1st & 2nd arch- preauricular sinus/cyst-common between tragus & crus of helix
-20th week-pinna acquires adult shape.initially located low on the side of neck,later moves more laterally & cranially
External auditory meatus-1st branchial cleft
- 16th week,cells proliferate from bottom of ectodermal cleft & forms meatal plug-recanalizes-forms epithelial lining of bony meatus-recanalization begins from the deeper part near the TM & progresses outwards & that explains why deeper meatus is sometimes developed while there's atresia of canal in the outer part-external ear forms fully by 28th wk
Tympanic membrane develops from all 3 germ layers
Middle Ear Cleft: eustachian tube, tympanic cavity, antrum, attic,mastoid air cells-develop from endoderm of tubotympanic recess- arises from 1st & partly from 2nd pharyngeal pouches.
Malleus & incus- 1st arch
stapes- 2nd arch except footplate & annular ligament
stapes footplate & annular ligament- from otic capsule
Membranous inner ear-starts in 3rd wk of fetal life-complete by 16th wk.ectoderm in the region of hind limb thickens to form an auditory placode-invaginated to form an auditory vesicle/otocyst.
Otocyst differentiates into endolymphatic duct & sac, the utricle, the semicircular ducts & saccule & cochlea.
Development of phylogenetically older part of labyrinth-pars superior(semicircular canals&utricle) takes place earlier than pars inferior-(saccule & cochlea)
The embryologic source & time of development of external & middle ears is quite independent of the development of the inner ear.It's therefore not unusual to see malformed inner ear in the presence of normal middle & external ears & vice versa.
The cochlea is developed sufficiently by 20th wks of gestation & the fetus can hear in the womb of the mother.
-faulty fusion between 1st & 2nd arch- preauricular sinus/cyst-common between tragus & crus of helix
-20th week-pinna acquires adult shape.initially located low on the side of neck,later moves more laterally & cranially
External auditory meatus-1st branchial cleft
- 16th week,cells proliferate from bottom of ectodermal cleft & forms meatal plug-recanalizes-forms epithelial lining of bony meatus-recanalization begins from the deeper part near the TM & progresses outwards & that explains why deeper meatus is sometimes developed while there's atresia of canal in the outer part-external ear forms fully by 28th wk
Tympanic membrane develops from all 3 germ layers
Middle Ear Cleft: eustachian tube, tympanic cavity, antrum, attic,mastoid air cells-develop from endoderm of tubotympanic recess- arises from 1st & partly from 2nd pharyngeal pouches.
Malleus & incus- 1st arch
stapes- 2nd arch except footplate & annular ligament
stapes footplate & annular ligament- from otic capsule
Membranous inner ear-starts in 3rd wk of fetal life-complete by 16th wk.ectoderm in the region of hind limb thickens to form an auditory placode-invaginated to form an auditory vesicle/otocyst.
Otocyst differentiates into endolymphatic duct & sac, the utricle, the semicircular ducts & saccule & cochlea.
Development of phylogenetically older part of labyrinth-pars superior(semicircular canals&utricle) takes place earlier than pars inferior-(saccule & cochlea)
The embryologic source & time of development of external & middle ears is quite independent of the development of the inner ear.It's therefore not unusual to see malformed inner ear in the presence of normal middle & external ears & vice versa.
The cochlea is developed sufficiently by 20th wks of gestation & the fetus can hear in the womb of the mother.
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