Ear Development Development

 The ear can be divided into three parts ◦ External Ear   external auditory canal ◦  auditory tube  auditory , , ◦  vestibular apparatus 

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  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  dorsomedial region elongate to form: ◦ endolymphatic appendage   rest region expanded to: ◦ pars superior  Utricle  semicircular canals  ◦ pars inferior  Its ventral tip elongate and coil  form  differentiate to spiral  Its rest gives rise to:  Saccule  connected to cochlea by

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- Medial - - 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- 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

 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

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 ◦ 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 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)  , , and cymba concha ◦ hillocks on 2nd arch (4-6)  , , 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)