Ear Flashcards
What gives rise to the internal ear?
Otic placode
Develops first
What gives rise to the middle ear?
1 and 2 pharyngeal arches (ossicles) and 1st pharyngeal pouch for lining of tympanic cavity and pharyngotympanic tube
What gives rise to the external ear?
1 pharyngeal arch
auricular hillocks
What week does the ear begin developing?
Week 4 (just like eye)
What are the direct derivatives of the otic placode?
Otic placode (ectoderm) forms the otic pit and then invaginates to form the Otic vesicle, which will become the membranous labyrinth
What are the regions of the otic vesicle?
Dorsal utricluar part- endolymphatic ducts, utricles, semicircular ducts
Ventral saccular part- saccule and cochlear ducts (which will grow into a spiral and then the organ of corti differentiates from it)
What tissue gives rise to the spiral and vestibular ganglia and the sensory nerves?
neuroectoderm
What forms the cartilage of the inner ear?
Mesenchyme around otic vesicle (otic capsule)
Major events of week 25
ossification of otic capsule complete, bony labrythne is fully formed and adult sized
Ossification of ossicles
What arch does the malleus and incus come from?
Pharyngeal arch 1 (merkels) *NC
What arch does stapes come from?
Arch2 *NC
Where is tensor tympani from?
Arch 1, mesoderm
What is stapedius from?
Arch 2, mesoderm
Where is the external acoustic meatus derived from?
1st pharyngeal cleft/groove, surface ectoderm
What composes the tympanic membrane?
Inner- endoderm
Middle- mesoderm (mesenchyme)
outer- ectoderm
Explain the 6 auricular hillocks
1-3- Arch 1- they make up the tragus, helical crus, and helix
4-6- Arch 2- they make up the anti helix, anti helix, and antitragus
**Mesenchyme, all surrounding pharyngeal groove/cleft 1
What causes embryo sensory deafness?
Inner ear or nerve issues, otic placode or neuroectoderm
cochlear implant
What causes embryo conduction deafness
External or middle ear issues, arch 1 and 2, pouch 1, cleft 1
What can be caused by accessory auricular hillocks?
Auricular appendage (skin tag)
What is anotia?
Absence of auricle, failure of mesenchyme to proliferate
What is microtia?
small auricle, usually associated with atresia of external acoustic meatus (cleft 1)
What is a pre auricular cyst?
Narrow tubes or shallow pits anterior to auricle.
Incomplete fusion of auricular hillocks or defective closure of the first part of the 1st pharyngeal cleft
