Jittipan Chavadej, Ph.D. Anatomy Dept., Fac. of Science Mahidol University yr., 2000

Jittipan Chavadej, Ph.D. Anatomy Dept., Fac. of Science Ma

hidol Universityyr.,2000

Mature components of the earsThe 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• i nner ear - cochlear duct - semicircular canal

Formation of the ear Dual origin

- thickened ectodermal

placode at rhombencephalon

- first and second branchial

arches

Rhombencephal on region:formati on of otic vesicle

s

Derivatives of th e 1st 2& nd branc

hial arches

Development of inner ear - Induction rhombencephalon~surfa

ce ectoderm

Otic placode Otic vesicle

Dorsal vestibular region

Ventral cochlear region

Rhombencephalon region:otic placode

, otic pit and otic vesicle

Ventral cochlear region

Saccule

Cochlear duct

Dorsal vestibular region

Utricle Semicircular

canals

Endolymphatic

duct

Membranous labyrinth

Development of the otic vesicle showing a dorsal utric ular portion with endolymphatic duct, and a ventral sa

ccular portion

Saccule, cochlea & organ of CortiOutgrowth of cochlear duct-spiral fashion 8th wk.- 21/2

turns Cochlear duct conect with saccu

le through ductus reuniens

Cochlear duct + mesenchyme

Scala media

Cartilageous shell

Scala vestibuli

Scala tympani

Vestibular mem. Basilar mem.

Organ of Corti (S.media & S.vestibuli

)

Development of the scala tympani & scala vestibuli

Note:the auditory nerve and spiral ganglion

Scala media - organ of Corti

Hair cells

Tectorial mem . (gelatineous substanc

e) - 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 ampull

ae in the semicircular canals

Development of the Middle EarExpansion of 1st pharyngeal pouch middle cavity & auditory tube

- * * Lining endodermal origin**

2nd - mo. blind end oftubotympan ic tube 1st pharyngeal cleft

Development of the middle ear

Note:tubotympanic recess, mesenchymal condensation

ear ossicle formation

6th -wk. condensation of mesench

yme (mesoderm):just dorsal to the end of tubo

tympanic end ear ossicles - Tympanic cavity ear ossicles in l

oose mesenchyme late pregnan cy: programmed cell death susp

ension of ear ossicles

- 2mo. after birth free moveme nt of ear ossicles

Development of the ear ossicles in the tympanic cavity

Note: malleus contact with eardrum, stapes contact wi th oval window and endodermal epithelium of tympani

c cavity

Dual origin of ear ossicles

• - malleus & incus mesoderm of 1st branchial arch

• - stapes mesoderm of 2nd branchia l arch

- *Tensor tympani mus. CN V

- *Stapedius CN VII

Development of the External Ear

Pinna - mesenchyme of 1st &2nd branchial arches:2nd mo. auricul

ar 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