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Ear Development Ear Development Ear Development Ear Development The ear can be divided into three parts ◦ External Ear Auricle external auditory canal ◦ Middle Ear tympanic cavity auditory tube auditory ossicles malleus, incus, stapes ◦ Inner Ear Cochlea vestibular apparatus semicircular canals Utricle Saccule Development of Inner Ear All of inner ear derivatives arise from ectoderm Late in 3rd week ◦ otic placode (disc) appears next to hindbrain During 4th week ◦ otic placode form: otic pit otic vesicle or otocyst Young neurons delaminate from ventral otocyst Form statoacoustic (vestibulocochlear) ganglion Rhombencephalon region:formation of otic vesicles Derivatives of the 1st & 2nd branchial arches Rhombencephalon region:otic placode , otic pit and otic vesicle Development of Inner Ear epithelial structures of Otic vesicle develops to membranous labyrinth dorsomedial region elongate to form: ◦ endolymphatic appendage endolymphatic sac rest region expanded to: ◦ pars superior Utricle semicircular canals endolymphatic duct ◦ pars inferior Its ventral tip elongate and coil form cochlear duct differentiate to spiral organ of Corti Its rest gives rise to: Saccule connected to cochlea by ductus reuniens 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 Sensory cells of Inner Ear specialized mechanotransducers arise in six prosensory regions within developing otic vesicle ◦ In the cochlea organ of Corti ◦ In the saccule and utricle Maculae ◦ in the semicircular canals Cristae All of these sensory regions innervated by the vestibulocochlear nerve 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 development flattened bilayered discs grow from the pars superior ◦ In the center of discs epithelial walls meet epithelium regresses leaving anlagen of semicircular canals 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 Bony labyrinth Beginning in the 9th week of development ◦ mesenchyme surrounding the membranous labyrinth chondrifies to form a cartilaginous otic capsule During 3-5th months ◦ Cartilage vacuolated to form perilymphatic space scala vestibuli scala tympani between 16-23rd weeks ◦ otic capsule ossifies petrous portion of temporal bone Development of Middle Ear first pharyngeal pouch ◦ tubotympanic recess tympanic cavity auditory (eustachian) tube Cartilaginous & Muscle precursors: ◦ 1st pharyngeal arch malleus and incus tensor tympani ◦ 2nd pharyngeal arch Stapes stapedius During 9th month ◦ surrounding mesenchyme around auditory ossicles removed ◦ tympanic cavity expands to enclose them ◦ tympanic cavity endoderm lines ossicles forms transient endodermal mesenteries until their definitive supporting ligaments develop ◦ tympanic cavity expands to form mastoid antrum tympanic membrane or eardrum ◦ outer lining of ectoderm ◦ inner lining of endoderm ◦ Intervening fibrous stratum derived from infiltrating neural crest cells 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 fTympanic cavity-ear ossicles in loose mesenchyme late pregnancy: programmed cell death suspension of ear ossicles g2 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 External Ear external auditory meatus ◦ develops from dorsal portion of 1st pharyngeal cleft At the beginning of 3rd month ◦ epithelial cells at bottom of meatus Proliferate Forms a solid epithelial plate meatal plug In 7th month ◦ plug dissolves ◦ Epithelial participates in definitive eardrum Development of External Ear The auricle develops from six auricular hillocks ◦ that arise during 5th week ◦ on 1st and 2nd pharyngeal arches From ventral to dorsal ◦ hillocks on 1st arch (1-3) tragus, helix, and cymba concha ◦ hillocks on 2nd arch (4-6) antitragus, antihelix, and concha During the 7th week ◦ auricular hillocks begin to enlarge, differentiate, and fuse As the face develops ◦ Auricle translocated from its original location low on the side of neck to a more lateral and cranial site 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 Auricular Defects Anotia ( first arch defect) Microtia ( atresia EAM) Preauricular pit Preauricular appendages - Hypothyroidism Rubella virus Trisomy 18 Anotia ( first arch defect) .
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