ENT Embryology Flashcards
Where is the internal ear derived from?
The internal ear derives from thickening of the surface (otic placodes) ectoderm on each side of the rhombencephalon
When do you first notice the development of the ear?
22 day old embryo
How are the otic/auditory vesicles formed?
They are invaginations of the otic placodes
What do you call the thickening of the surface of ectoderm?
Otic placodes
Where do parts of the middle ear develop from?
Tympanic cavity - develops from the first pharyngeal pouch
Ossicles - malleus and incus develop from the cartilage of the 1st pharyngeal arch and stapes develops from that of the 2nd pharyngeal arch
What do the auditory vesicles develop into?
It divides into a ventral and dorsal component that form the membranous labyrinth
Ventral component - gives rise to the saccule and cochlear duct
Dorsal component - forms the utricle, semicircular canals, and endolymphatic duct
Name a common complication of middle ear infection
Expansion of the inflammations into the antrum and mastoid air cells
State the structure that communicates the middle ear and nasopharyngeal.
Eustachian/auditory tube
How does the tympanic cavity develop?
The tympanic cavity develops from the 1st pharyngeal pouch
The pouch expands laterally and comes in contact with the floor of the 1st pharyngeal cleft
The distal part (tubotympanic recess), widens and gives rise to the primitive tympanic cavity
The proximal part remains narrow and forms he auditor tube (eustachian tube)
What happens to the epithelium of the tympanic cavity after birth?
It invades the one of the developing mastoid process to form epithelial-lined sacs (pneumatization process)
Later, most of the mastoid air sacs come in contact with the antrum and tympanic cavity
Describe how the ossicles develop.
The ossicles malleus and incus develop from the cartilage of the 1st pharyngeal arch, whereas stapes develops from that of the 2nd pharyngeal arch
They appear in the 1st half of fetal life and are embedded in mesenchyme until the 8th month when surrounding tissue dissolves.
When this happens, the endodermal epithelial lining of the primitive tympanic cavity then expands along the wall of the newly developing space
(The tympanic cavity is now twice as large as before)
When the ossicles are entirely free from the surrounding mesenchyme, the endodermal epithelium connects them to the wall of the cavity
The ligaments of the ossicles develop later within these mesentaries
During fetal life, the tympanic cavity expands for dorsally by vacuolization of surrounding tissue to form tympanic antrum
Innervation of tensor tympani
Mandibular branch of trigeminal nerve (V3)
Where do the different parts of the external ear develop from?
External auditory meatus - dorsal portion of the 1st pharyngeal cleft
Eardrum - 1. Ectodermal lining at the bottom of the auditory meatus 2. Endodermal lining of the tympanic cavity 3. Intermediate layer of connective tissue that forms the fibrous stratum
Auricle - 6 mesenchymal proliferations at the dorsal ends of the 1st and 2nd pharyngeal arches surrounding the 1st pharyngeal cleft
Name 2 auricular abnormalities
Pits - may indicate abnormal development of the auricular hillocks
Appendages/skin tags - may be due to accessory hillocks
The malleus and incus develop from what structures in the 1st pharyngeal arch?
Mekcle’s cartilage
