Ear Development Flashcards
What is the critical period of ear development?
When do ears finish developing completely?
week 4-8
week 20
What parts of the ear develop from pharyngeal arches?
external and middle ear
(middle ear derived from surface ectoderm)
What does the auricle form from?
1st and 2nd pharyngeal arches
auricular hillocks = mesenchyme w/ NC covered w/ ectoderm
What innervates the external ear?
CN V3: auriculotemporal
Great auricular N (C2, C3)
Cn X: auricular branches
CN 7
What causes auricular skin tags?
abnormal migration of ectoderm
if cartilage is present –> also abnormal migration of NC cells
What is anotia and what causes it?
no external ear
NC cells of arches 1 and 2 don’t form right
auricular hilloxes didnt form
How does the external auditory meatus form?
invagination of ectoderm from 1st arch = 1st pharyngeal cleft –> meatal plug of ectoderm –> eventually apoptoses to form hole
What is the inner ear derived from?
surface ectoderm near hindbrain
otic placode –> otic pit (invagination) –> otic vesicle (pouch) –> gives rise to membranous labyrinth
What part of the otic vesicle becomes the utricle?
Saccule?
dorsal –> utricle and semicircular ducts
ventral –> sacule, cochlea
What does development of the utricle and other dorsal inner ear structures depend on?
DIx5 and DIx6
What does the lateral semicircular canal development depend on?
Otx1
(in addn to DIx5 and Dlx6)
What does development of the cochlear duct depend on?
Pax6
What do hair cells develop from?
ectoderm of otic vesicle
What do the ampullae hair cells of semicircular canals sense?
acceleration
What do the hair cells of the macula of utricle and saccule sense?
gravity
What do the hair cells of the organ of corti of cochlea sense?
sound vibration
What is the innervation of the inner ear?
What do the nerves develop from?
cranial nerve 8 = vestibulocochlear n
vestibular ganglion = surface ecto and NC cells
Spiral ganglion = surface ecto
What is important about perilymph?
perilymphatic duct usually patent –> free passage from subarachnoid space into inner ear
similar in ion content to CSF = high Na, low K and protein
What is important about endolymph?
stria vascularis produces endolymph
imilar in ion content to ICF = high K and protein, low Na
endolymphatic sac stores endolymph
What does the bony labyrinth develop from?
condensation of mesoderm/mesenchyme
Where is the organ of corti and what does it develop from?
in the middle of the cochlea = membranous labyrinthe
develops from surface ectoderm
How does external auditory meatus form?
1st pharyngeal cleft ectoderm –> external auditory meatus
How does the tympanic cavity form?
first pharyngeal pouch endoderm –> tubotympanic recess –> grows up and forms around developing ossicles
endoderm contributes to the eardrum
What is the tympanic membrane derived from?
surface ectoderm (outer surface)
mesoderm
endoderm (inner surface)
What do the ossicle develop from?
malleus and incus form 1st arch
stapes from 2nd arch
NC cells
then covered w/ endoderm epithelium
What nerves innervate the muscles of the ear?
tensor tympani: trigeminal N (5)
stapedius: Facial N (7)
what do the muscles of the ear develop from?
Tensor tympani = 1st pharyngeal arch mesoderm
Stapedius = 2nd pharyngeal arch mesoderm
What can cause congenital deafness?
maldev. of sound-conduction apparatus of middle and external ears (1st arch syndrome, bone abnormalities, congenital fixation of the stapes)
neurosensory structures of the inner ear
How is rubella infection related to deafness?
mom w/ rubella during 7-8th week –> can cause defects of spiral organ and deafness
