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