1. DEVELOPMENT OF EAR By
Dr Samina Anjum

2. DEVELOPMENT OF EAR Ear is composed of three anatomical parts
External ear (Collection of sound waves)
auricle, external auditory meatus, external layer of tympanic membrane
Middle ear (conduction of sound waves)
3 auditory ossicles, tympanic cavity, auditory tube
Internal ear (hearing & balance)
vestibulocochlear organ which converts waves into nerve impulses & register changes in equilibrium

3. DEVELOPMENT OF INTERNAL EAR
Otic placodes -- on each side of myelencephalon
Inductive influence – notochord, paraxial mesoderm
Otic pit, otic vesicle, loses connection from surface ectoderm
Two parts of otic vesicle---- memb. labyrinth
Ventral component---- saccule & cochlear duct
Dorsal component---- utricle, semicircular canals, & endolymphatic duct

4. SACCULE, COCHLEA, & ORGAN OF CORTI
In 6thweek saccule forms a tubular out pocketing --- cochlear duct completes 2.5 turns in 8th week
Connected with saccule through ductus reuniens
Surrounding mesenchyme differentiates into cartilage
In10th week vacuoles develop in cartilage & two perilymphatic spaces formed
Scala tympani & scala vestibuli
Vestibular & basilar membranes
Spiral ligament, modiolus
Cells in wall of cochlear duct differentiate into organ of corti; forms two ridges
inner ridge---- spiral limbus--- tectorial membrane
Outer ridge row of inner hair cells
3-4 rows of outer hair cells
Statoacoustic ganglion ---- wall of otic vesicle & neural crest cells

5. DERIVATIVES OF OTIC VESICLE

6. FORMATION OF SCALA VESTIBULI & SCALA TYMPANI

7. DEVELOPMENT OF ORAN OF CORTI

8. UTRICLE & SEMICIRCULAR CANALS
Semicircular canals (SSC) appear as out pocketings of utricular part of otic vesicle
Central parts of these diverticula fuse & disappear
Peripheral unfused parts of diverticula become SSC

9. One end of each canal dilates to form crus ampullare
while crus nonampullare, does not widen. Since two
of latter type fuse, however, only five crura enter
the utricle, 3 with an ampulla & 2 without
Cells in the ampulla forms a crest, crista ampullaris
containing sensory cells for maintenance of equilibrium
Similarly specialized receptor areas macula develop in utricle & saccule
Sensory areas are stimulated by positional changes
& impulses re transmitted via vestibular ganglion to brain through CN- VIII

10. DEVELOPMENT OF MIDDLE EAR
Endoderm of 1st pharyngeal pouch forms the tubotympanic recess which comes in contact with 1st pharyngeal cleft to form the external auditory meatus
Distal end is expanded Tympanic cavity
Proximal end is narrow auditory tube

11. EAR OSSICLES Malleus & incus---cartilage of 1st pharyngeal arch
Stapes-----cartilage of 2nd pharyngeal arch
Remain embedded in mesenchyme till 8th month when surrounding tissue dissolves

12. Cont…
The endodermal epithelial lining of tympanic cavity then extends along the newly developing space
When ossicles are entirely free of surrounding mesenchyme, the endodermal epithelium connects them in a mesentery like fashion to the wall of cavity
Tympanic cavity expands dorsally by vacuolization of surrounding tissue to form tympanic antrum

13. DEVELOPMENT OF EXTERNAL EAR
Begins at 3rd month
External auditory meatus --- 1st pharyngeal cleft
Ectodermal cells at the bottom of cleft proliferate to form a solid epithelial plate, the meatal plug
During 7th month the plug dissolves to form internal part of external auditory meatus
Tympanic membrane is the 1st pharyngeal membrane b/w cleft & pouch

14. AURICLE
Develops from 6 mesenchymal proliferations in 1st & 2nd pharyngeal arches surrounding the first cleft
These swellings are auricular hillocks 3 on each side of external meatus

15. Cont… These swellings later fuse to form definite auricle
As fusion of auricular hillocks is complicated developmental abnormalities of the auricle are common
Lobule is the last part to develop
As mandible develops the auricle moves to their normal position at the sides of head

16. CONGENITAL ANOMALIES Congenital deafness
Mal development of internal ear or auditory ossicles or ear drum
External ear defects
Due to chromosomal abnormalities

17. Thank You