Embryo of Ear and Nose

1. EMBRYOLOGY OF THE EAR
AND NOSE
BY Dr.Sneha.S.N.
CO-MODERATOR-Dr.Shweta Jaitly.
MODERATOR-Dr.(Prof) Gul Motwani.

2. • The first indication of the developing ear can be found in embryos of
approximately 22 days as a thickening of the surface ectoderm on
each side of the rhombencephalon.
These thickenings-the otic placodes, invaginate rapidly otic or
auditory vesicles(otocysts)
• During later development, each vesicle divides into
(a)Ventral component saccule and cochlear duct.
(b) Dorsal component utricle, semicircular canals,and
endolymphaticduct.

4. COCHLEA
• In the sixth week of development, the saccule forms a tubular
outpocketing at its lower pole.
• This outgrowth, the cochlear duct, penetrates the surrounding
mesenchyme in a spiral fashion until at the end of the 8TH week it has
completed 2.5turns.
• Its connection with the remaining portion of the saccule is then
confined to a narrow pathway, the ductus reuniens.

6. • Mesenchyme surrounding the cochlear duct soon differentiates into
cartilage.
• In 10th week, this cartilaginous shell undergoes vacuolization, 2
perilymphatic spaces,the scala vestibule and scala tympani.
• The lateral wall of the cochlear duct remains attached to the
surrounding cartilage by the spiral ligament.
• The median angle is connected to and partly supported by a long
cartilaginous process, the modiolus, the future axis of the bony
cochlea.

8. Organ of corti
• The epithelial cells of the cochlear duct form two ridges: the inner ridge,
and the outer ridge.
• The inner ridge forms the spiral limbus.
• The outer ridge forms 1 row of inner and 3-4 rows of outer hair cells.
• They are covered by the tectorial membrane, a fibrillar gelatinous
substance attached to the spiral limbus that rests with its tip on the hair
cells.
• The sensory cells and tectorial membrane together constitute the organ
of Corti.

10. THE SEMICIRCULAR CANALS
• During the 6th week of development, semicircular canals appear as
flattened outpocketings of the utricular part of the otic vesicle.
• Central portions of the walls of these outpocketings eventually
appose each other and disappear, giving rise to three semicircular
canals.
• Whereas one end of each canal dilates to form the crus ampullare,
the other, the crus nonampullare, does not widen.
• Since two of the latter type fuse, however, only five crura enter the
utricle, three with an ampulla and two without.

12. • During formation of the otic vesicle, a small group of cells breaks
away from its wall and forms the statoacoustic ganglion.
• Other cells of this ganglion are derived from the neural crest.
• The ganglion subsequently splits into cochlear and vestibular
portions, which supply sensory cells of the organ of Corti and those of
the saccule, utricle, and semicircular canals, respectively

13. Congenital anomalies of inner ear
1.Malformatins limited to
membranous labyrinth:
A)complete dysplasia(Seimann-
Bing).
B) Limited-
cochleosacular(schiebe) -cover
basal turn(Alexander).
2. Malformations of osseous and
membranous labyrinth:
A)Complete labrynthine
aphasia(Michel).
B) cochlear anomalies:
•Cochlear aphasia.
•Cochlear hypoplasia.
•Incomplete partition.
•Common cavity.

14. 2.Labrynthine anomalies:
A) semicircular aphasia.
B). Semicircular dysplasia.
3.Aqueductal anomalies
A) Enlargement of vestibular aqueduct.
B) Enlargement of cochlear aqueduct.
4.IAC abnormalities.
A) Narrow IAC.
B) Wide IAC.

15. TYMPANIC CAVITY AND AUDITORY TUBE
• The tympanic cavity, which originates in the endoderm, is derived
from the first pharyngeal pouch.
• This pouch expands in a lateral direction and comes in contact with
the floor of the first pharyngeal cleft.
• The distal part of the pouch, the tubotympanic recess, widens
primitive tympanic cavity.
• The proximal part remains narrow and forms the eustachian tube.

16. • During late fetal life, the tympanic cavity expands dorsally by
vacuolization of surrounding tissue to form the tympanic antrum.
• After birth, epithelium of the tympanic cavity invades bone of the
developing mastoid process, and epithelium- lined air sacs are
formed(pneumatization)

17. ossicles
• The malleus and incus are derived from cartilage of the first pharyngeal
arch.
• The stapes is derived from cartilage of the second arch.
• The ossicles remain embedded in mesenchyme until the 8th month,
when the surrounding tissue dissolves.
• When the ossicles are entirely free of surrounding mesenchyme, the
endodermal epithelium connects them in a mesentery-like fashion to
the wall of the cavity.
• The supporting ligaments of the ossicles develop later within these
mesenteries.

18. • Stapedius muscle is derived from the second pharyngeal arch.
• Tensor tympani is a derivative of first pharyngeal arch.
• Tensor veli palatini is a derivative of the first pharyngeal arch.

20. EAC
• The external auditory meatus develops from the dorsal portion of
the first pharyngeal cleft.
• At the beginning of the 3RD month, epithelial cells at the bottom of
the meatus proliferate, forming a solid epithelial plate, the meatal
plug.
• In the 7TH month, this plug dissolves and the epithelial lining of the
floor of the meatus participates in formation of the definitive
eardrum.

21. • Beginning at 8 weeks, the inferior portion of the first branchial groove
deepens again, forming the primary external auditory canal, which
corresponds to the fibrocartilaginous canal of the adult.
• A cord of epithelial cells at the depths of the primary external
auditory canal grows medially into the mesenchyme to terminate in a
solid (meatal) plate.
• After the fifth month that the cord splits open, initially at its medial
terminus, forming the bony external auditory canal by the seventh
month.

22. TYMPANIC MEMBRANE
• The eardrum is made up of
• (a) ectodermal epithelial lining at the bottom of the auditory meatus,
• (b)endodermal epithelial lining of the tympanic cavity.
• (c) an intermediate layer of connective tissue that forms the fibrous
stratum

23. AURICLE
• The auricle develops from 6 mesenchymal proliferations at the dorsal
ends of the first and second pharyngeal arches, surrounding the first
pharyngeal cleft.
• These swellings (auricular hillocks), three on each side of the
external meatus, later fuse and form the definitive auricle

26. Facial development.
• Facial development takes place mainly betweenthe 4th and 8th weeks
of intrauterine life.
• The facedevelops from 5 facial swellings that surround the
stomodeum or primitivemouth by the end of the 4th week.
• The swellings consist of:
• A central unpaired process called the frontonasal process.
• Pair of maxillary processes.
• Pair ofmandibular processes.

28. • 5th week pair of ectodermal thickenings appear on the frontonasal
process-nasal placodes.
• 6th week the ectoderm in the center of each nasal placode
invaginates to form an oval nasal pit.
• The raised rims of these nasal pits form the lateral and medial nasal
processes.
• 6th and 7th weeks the maxillary processes on either side
increase in size and grow medially.
• This medial migration of the maxillary processes causes the medial nasal
processes to move towards each other

31. • As the maxillary processes grow medially, they fuse first with the
lateral nasal process and then with the medial nasal process. This
separates the nasal pits from the stomodeum.
• The medial nasal processes fuse with each other to form the
intermaxillary process.
• The central tissues of the intermaxillary process get pushed upwards
to form the nasal prominence.
• The intermaxillary process forms the central bridge of the nose and
the central portionof the upper lip called the philtrum.

33. Nasal cavity
• At the end of the 6th week, the nasal pits deepen and coalesce to
form a single cavity behind the intermaxillaryprocess.
• This cavity is initially separated from the stomodeum lying below itby
a thin membrane called the oronasal membrane.
• This membrane ruptures during the 7th week to form the primitive
choana, which is the opening of the primitive nasal cavity into the
stomodeum.

36. Septum and lateral wall.
• The intermaxillary process grows backward to form the nasal septum.
• The lateral nasal processes enlarge to form the nasal alae. They also
grow backwards to form the lateral nasal wall.
• This developing lateral nasal wall shows multiple anteroposterior
elevations, which are finally reduced to three or occasionally four in
number. These form the turbines.

38. Development of NLD
• The maxillary processes fuse with the lateral nasal processes.
• The junction of their fusion is marked by a groove called the
nasolacrimal or naso-opticgroove.
• By the 7th week, this groove invaginates into the underlying
mesenchyme to form the nasolacrimal duct.
• The canalization of nasolacrimal duct continues throughout
pregnancy and may not be complete till after birth.

39. Floor of nasal cavity
• The floor of the nasal cavity, which is the hard palate, is formed during the
8th and 9th week.
• The medial surfaces of the maxillary processes form thin medial extensions
called palatine shelves.
• These shelves first grow downwards on either side of the developing
tongue; but by the end of the 9th week, they rotate upwards into a
horizontal position.
• They then fuse with each other in the midline and with the primary palate
anteriorly to form the secondary palate.
• The secondary palate also fuses with the lower border of the developing
nasal septum.

44. THANK YOU