Ear Development

Question 1

What is the critical period of ear development?

When do ears finish developing completely?

Answer 1

week 4-8

week 20

Question 2

What parts of the ear develop from pharyngeal arches?

Answer 2

external and middle ear

(middle ear derived from surface ectoderm)

Question 3

What does the auricle form from?

Answer 3

1st and 2nd pharyngeal arches

auricular hillocks = mesenchyme w/ NC covered w/ ectoderm

Question 4

What innervates the external ear?

Answer 4

CN V3: auriculotemporal

Great auricular N (C2, C3)

Cn X: auricular branches

CN 7

Question 5

What causes auricular skin tags?

Answer 5

abnormal migration of ectoderm

if cartilage is present –> also abnormal migration of NC cells

Question 6

What is anotia and what causes it?

Answer 6

no external ear

NC cells of arches 1 and 2 don’t form right

auricular hilloxes didnt form

Question 7

How does the external auditory meatus form?

Answer 7

invagination of ectoderm from 1st arch = 1st pharyngeal cleft –> meatal plug of ectoderm –> eventually apoptoses to form hole

Question 8

What is the inner ear derived from?

Answer 8

surface ectoderm near hindbrain

otic placode –> otic pit (invagination) –> otic vesicle (pouch) –> gives rise to membranous labyrinth

Question 9

What part of the otic vesicle becomes the utricle?

Saccule?

Answer 9

dorsal –> utricle and semicircular ducts

ventral –> sacule, cochlea

Question 10

What does development of the utricle and other dorsal inner ear structures depend on?

Answer 10

DIx5 and DIx6

Question 11

What does the lateral semicircular canal development depend on?

Answer 11

Otx1

(in addn to DIx5 and Dlx6)

Question 12

What does development of the cochlear duct depend on?

Answer 12

Pax6

Question 13

What do hair cells develop from?

Answer 13

ectoderm of otic vesicle

Question 14

What do the ampullae hair cells of semicircular canals sense?

Answer 14

acceleration

Question 15

What do the hair cells of the macula of utricle and saccule sense?

Answer 15

gravity

Question 16

What do the hair cells of the organ of corti of cochlea sense?

Answer 16

sound vibration

Question 17

What is the innervation of the inner ear?

What do the nerves develop from?

Answer 17

cranial nerve 8 = vestibulocochlear n

vestibular ganglion = surface ecto and NC cells

Spiral ganglion = surface ecto

Question 18

What is important about perilymph?

Answer 18

perilymphatic duct usually patent –> free passage from subarachnoid space into inner ear

similar in ion content to CSF = high Na, low K and protein

Question 19

What is important about endolymph?

Answer 19

stria vascularis produces endolymph

imilar in ion content to ICF = high K and protein, low Na

endolymphatic sac stores endolymph

Question 20

What does the bony labyrinth develop from?

Answer 20

condensation of mesoderm/mesenchyme

Question 21

Where is the organ of corti and what does it develop from?

Answer 21

in the middle of the cochlea = membranous labyrinthe

develops from surface ectoderm

Question 22

How does external auditory meatus form?

Answer 22

1st pharyngeal cleft ectoderm –> external auditory meatus

Question 23

How does the tympanic cavity form?

Answer 23

first pharyngeal pouch endoderm –> tubotympanic recess –> grows up and forms around developing ossicles

endoderm contributes to the eardrum

Question 24

What is the tympanic membrane derived from?

Answer 24

surface ectoderm (outer surface)

mesoderm

endoderm (inner surface)

Question 25

What do the ossicle develop from?

Answer 25

malleus and incus form 1st arch

stapes from 2nd arch

NC cells

then covered w/ endoderm epithelium

Question 26

What nerves innervate the muscles of the ear?

Answer 26

tensor tympani: trigeminal N (5)

stapedius: Facial N (7)

Question 27

what do the muscles of the ear develop from?

Answer 27

Tensor tympani = 1st pharyngeal arch mesoderm

Stapedius = 2nd pharyngeal arch mesoderm

Question 28

What can cause congenital deafness?

Answer 28

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

Question 29

How is rubella infection related to deafness?

Answer 29

mom w/ rubella during 7-8th week –> can cause defects of spiral organ and deafness