Development of ear ppt

Embyaology

1. Development of Ear Dr safika zaman, Dept of ENT & Head Neck surgery VIMS, RKMSP

2. embryogenesis During embryogenesis the ear develops as three distinct structures: the inner ear, the middle ear and the outer ear.Each structure originates from a different germ layer: the ectoderm,endoderm  and mesoderm.

3. Arches

4. External Ear The development of the pinna starts at 4 weeks as tissue condensations of the mandibular and hyoid arches appear at the distal portion of the first branchial groove.

5. External ear The hillocks fuse into an anterior fold of mandibular arch origin and a posterior fold of hyoid arch origin, oriented about the first branchial groove. The folds unite at the upper end of this groove

6. External ear Adult configuration is achieved by the fifth month, independent of developmental progress in the middle ear.

7. External auditory canal The dorsal part of the first branchial groove, which gives rise to EAC, progressively deepens during the second month. The ectoderm of the groove invades on the endoderm of the tubotympanic recess, During the sixth week, a mesodermal ingrowth breaks this contact. This corresponds to fibrocartilaginous canal

8. TYMPANOMASTOID COMPARTMENT AND EUSTACHIAN TUBE 3-week stage as an outpouching of the first pharyngeal pouch known as the tubotympanic recess. The endodermal tissue of the dorsal end of this pouch eventually becomes the eustachian tube and tympanic cavity

9. Pneumatisation of middle ear and mucosal folds The terminal end of the first pharyngeal pouch buds into four sacci ( anticus , posticus , superior,and medius '"), which expand to progressively pneumatize the middle ear and the epitympanun . Expansion of the sacci the interface between two sacci gives rise to mucsal folds.

10. Cont …

11. Ossicular development ossicular development in the occurs at approximately 4 weeks as an inter branchial bridge appears, connecting the upper end of that portion of the first branchial arch referred to as the mandibular visceral bar and the central region of the hyoid (second branchial arch) visceral bar.

12. Derivatives of branchial arches

13. Development of otic labyrinth Otic placode appears by the 3 rd week. Invaginates into the underlying mesenchyme, forming the auditory pit. Expansion of otic pit creating otic vesicle. Elongation of the otocyst and the appearance of three deepening folds the utricle with its three semicircular ducts, the endolymphatic duct and sac and the saccule with its cochlear duct.

14. Cont …

15. Development of Perilymphatic labyrinth The perilymphatic labyrinth comprises the fluid tissue space The perilymphatic cistern of the vestibule, scala tympani,scala vestibuli , perilymphatic space of the semicircular canals, fissula ante fenestram , fissula post fenestram , and periotic duct At 8th week perilymphatic space formation starts from the surrounding Mesodermal tissue .

16. Development of otic capsule Starts at 4 th week Becomes petrous part of temporal bone. Develops from mesenchyme that is differentiates into embryonic cartilage. A total of 14 center eventually appear and fuse to complete the ossification of the otic capsule.

17. DEVELOPMENT OF THE ACOUSTIC NERVE AND GANGLION At the 4th and 5th weeks, the acoustic ganglion divides into superior and inferior segments. The superior segment innervate the crista of the superior and lateral semicircular ducts as well as the utricular macula. the inferior segment divides into upper and lower portions. The upper portion supplies to the saccular macula and to the crista of the posterior semicircular duct, the lower portion innervates the organ of Corti .

18. DEVELOPMENT OF THE FACIAL NERVE AND GENICULATE GANGLION At about 4 weeks, the facial nerve and its geniculate ganglion begin to develop from primordial tissue, arising from the rhomben cephalon .

19. the squama is disproportionately large . The mastoid process is essentially non-existent. the tympanic bone is a relatively flat ring. entire temporal bone in the neonates inferolateral. The facial nerve, is more lateral. The foramen of Huschke Neonatal Temporal bone

20. Thank you