Ear Development Flashcards
How is the external ear formed?
It is derived from the 1st and 2nd pharyngeal arches. Auricular hillocks develop on the arches and migrate to for the external components of the ear.
What is the makeup of the auricular hillocks?
They are made of NCCs with surface ectoderm overlying them.
Innervation to the external ear (4):
CN V3 - auriculotemporal n.
C2-3 - great auricular n.
CN X - auricular branches
CN VII
Auricular skin tags can include which embryonic layers?
Surface ectoderm, possibly NCCs
What is anotia?
Absence of external ear. Auricular hillocks didn’t form.
How is the external auditory meatus formed?
Invagination of surface ectoderm from the 1st pharyngeal cleft forms the meatal plug. Cells then undergo apoptosis and leave a tube.
How is the inner ear formed?
Surface ectoderm invaginates and becomes the otic placode –> otic pit –> otic vesicle.
What is the membranous labyrinth from?
Otic vesicle (surface ectoderm)
What genes induces formation of the utricle?
Dlx5 and Dlx6
What does the utricle include?
Semicircular ducts and ampullae
What is the lateral canal part of?
What gene induces its formation?
Part of the utricle.
Otx1
What does the saccule include?
Cochlear duct. ductus reunions, organ of Corti.
What are hair cells from?
Otic vesicle –> surface ectoderm
Hair cells in the ampullae detect what?
Acceleration
Hair cells in the macula of the saccule detect what?
Gravity
Hair cells of the organ of Corti detect what?
Sound vibration
What innervates the inner ear?
CN VIII.
Vestibular ganglion and spiral (cochlear) ganglion.
What is the vestibular ganglion from?
What is the cochlear ganglion from?
Vestibular - NCC
Cochlear - surface ectoderm
How can perilymph enter the subarachnoid space?
The perilymphatic duct is usually patent and allows a passageway into the subarachnoid space.
How is the ion content of perilymph characterized?
Like CSF.
High Na+, low K+ and protein
What produces endolymph?
Where is it stored?
Stria vascularis produces it.
Endolymphatic sac stores it.
What is the ion content of endolymph?
Like ICF.
High K+ and protein, low Na+.
What forms the bony labyrinth?
Condensation of mesenchyme - mesoderm.
How are the semicircular ducts, scala vestibuli and scala tympani formed in the bony labyrinth?
Apoptosis of the cells within the bony labyrinth.
Bony labyrinth is from which bone?
Petrous part of temporal bone
How is the middle ear formed?
The 1st pharyngeal cleft (ectoderm) formd the ext. auditory meatus meets with the 1st pharyngeal pouch (endoderm).
What makes up the tympanic membrane? (3)
Ectoderm, mesoderm, endoderm
What makes the ossicles?
NCCs.
Malleus and incus from 1st arch and stapes from 2nd arch.
What is tensor tempani m. from?
What is stapedius m. from?
1st pharyngeal arch mesoderm.
2nd pharyngeal arch mesoderm.
Rubella infection in 7-8 wks can cause defects in what?
Spiral organ (organ of Corti) and deafness.
