Anatomy Dept., Fac. of Science Mahidol University Development of the Ear Jittipan Chavadej, Ph.D. Anatomy Dept., Fac. of Science Mahidol University yr.,2000
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
Formation of the ear Dual origin - thickened ectodermal placode at rhombencephalon - first and second branchial arches
Rhombencephalon region:formation of otic vesicles Derivatives of the 1st & 2nd branchial arches
Development of inner ear Induction - rhombencephalon~surface ectoderm Otic placode Otic vesicle Dorsal vestibular region Ventral cochlear region
Rhombencephalon region:otic placode , otic pit and otic vesicle
Membranous labyrinth Ventral cochlear region Saccule Cochlear duct Dorsal vestibular region Utricle Semicircular canals Endolymphatic duct
Development of the otic vesicle showing a dorsal utricular portion with endolymphatic duct, and a ventral saccular portion
Saccule, cochlea & organ of Corti Outgrowth of cochlear duct-spiral fashion 8th wk.- 21/2 turns Cochlear duct conect with saccule through ductus reuniens
Cochlear duct + mesenchyme Cartilageous shell Scala media Scala tympani Scala vestibuli Basilar mem. Vestibular mem. (S.media & S.vestibuli) Organ of Corti
Development of the scala tympani & scala vestibuli Note:the auditory nerve and spiral ganglion
Scala media - organ of Corti Hair cells Tectorial mem. (gelatineous substance) 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 ampullae in the semicircular canals
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
Development of the middle ear Note:tubotympanic recess, mesenchymal condensation ear ossicle formation
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
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
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
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
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
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