Ear Embryology

Question 1

What does the external ear develop from?

Answer 1

the 1st pharyngeal cleft, plus mesenchymal hillocks associated with the 1st and 2nd pharyngeal arches

Question 2

What does the middle ear develop from?

Answer 2

the 1st pharyngeal pounch\

but the ossicles are from the 1st and 2nd pharyngeal arches

Question 3

What does the inner ear devlop from?

Answer 3

the otic vessicle

Question 4

How is the otic vesicle formed?

Answer 4

the otic placode is an area of thickened surface ectoderm aadjacent to eh hindbrain

it thickens, forms a depression and pinches off to sink into the surrounding mesenchyme

Question 5

What will the otic vesicle induce the surrounding mesenchyme to form?

Answer 5

the bony labyrinth (meaning the otic vesicle transofrms into the membranous labyrinth)

Question 6

What part of the brain takes care of induction of the otic placodes

Answer 6

the hindbrain

Question 7

What ganglion does oart of the otic vesicle develop into?

Answer 7

the statoacoustic ganglion

Question 8

THe otic vessicle sort of divides into what two sections?

Answer 8

the dorsal utricular part and the ventral saccular part

Question 9

What does the utricular part of the otic vessicle give rise to?

Answer 9

the semicircular ducts utricle and endolymphatic duct

Question 10

What does the saccular part of the otic vesicle give rise to?

Answer 10

the saccule, cochlear duct, ductus reuniens (connects the cochlea to the rest of the labyrinth)

Question 11

HOw do the semicircular ducts for?

Answer 11

the utricular porition of the otic vesicle form plate-like outpocketings oriented at right angles to one another. The walls oppose one another and the cells in the middle portion will leave, leaving just hollow semicircular ducts

the wide areas are the ampulae, attached to the utricle

Question 12

Besides the otic vesicle, what cells help to form the statoacoustic ganglion?

Answer 12

neural crest cells

Question 13

What does the statoacoustic ganglion split to form?

Answer 13

the vestibular ganglion and the spiral ganglion

Question 14

What organ develops in the wall of the cochlear duct?

Answer 14

organ of corti

Question 15

THe otic vesicle induces condensation of the surorunding mesenchyme to form the otic capsule. The outer portion of this ossifies to form the bony labyrinth and the inner cartilage vacuolizes to form what three spaces?

Answer 15

scala vestibuli, scala tympani, and cochlear duct (scla media)

Question 16

What does the vestibular membane separate? WHat does the basilar membrane separate

Answer 16

vestibulra separates scala vestibuli and cochlear duct (easy

basilar membrane is between the scala tympani and cochlear duct (it’s what the organ of corti rests on)

Question 17

What forms the attachment of the cochlear duct tot he cartilage?

Answer 17

spiral ligament (on the inner aspect of the cochlea)

Question 18

How is the tympanic membrane formed?

Answer 18

1. the first pharyngel pouch evaginates while the firs tpharyngeal groove invaginates
2. They grow towards each other until there’s only a small porion of second pharyngeal arch mesodemr between them.

Question 19

During development, what do the ectodermal cells form outside the TM?

Answer 19

they proliferate and form a plug, which will eventually disappear

Question 20

What forms the maleus and incus? WHat forms the stapes?

Answer 20

mesoderm from the 1st pharyngeal arch

mesoderm from the 2nd pharyngeal arch

Question 21

What arch forms the tensor tympani? Innervation?

What arch forms the stapes? Innervation?

Answer 21

1st arch = tensor, trigeminal

2nd arch - stapes, facial

Question 22

Describe development of the auricle.

Answer 22

you get six auricular hillocks developing by mesenchyme proliferation

the anteiror three are from the first arch and the posteior three are from the second arch

the center is the first pharyngeal cleft

These hillocks will eventually form the outer structures of the auricle

Question 23

Although the pinna is formed by the 1st and 2nd pharyngeal arches aroudn the 1st pharyngeal cleft, whaat makes their innervation odd?

Answer 23

the anterior portion is supplied by the trigeminal as you’d espect from someone arising form the 1st pharyngeal arch, but the posterior half isn’t supplied by the facial, it’ supplied by the cervical plexus