Ear Development

Question 1

How is the external ear formed?

Answer 1

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.

Question 2

What is the makeup of the auricular hillocks?

Answer 2

They are made of NCCs with surface ectoderm overlying them.

Question 3

Innervation to the external ear (4):

Answer 3

CN V3 - auriculotemporal n.
C2-3 - great auricular n.
CN X - auricular branches
CN VII

Question 4

Auricular skin tags can include which embryonic layers?

Answer 4

Surface ectoderm, possibly NCCs

Question 5

What is anotia?

Answer 5

Absence of external ear. Auricular hillocks didn’t form.

Question 6

How is the external auditory meatus formed?

Answer 6

Invagination of surface ectoderm from the 1st pharyngeal cleft forms the meatal plug. Cells then undergo apoptosis and leave a tube.

Question 7

How is the inner ear formed?

Answer 7

Surface ectoderm invaginates and becomes the otic placode –> otic pit –> otic vesicle.

Question 8

What is the membranous labyrinth from?

Answer 8

Otic vesicle (surface ectoderm)

Question 9

What genes induces formation of the utricle?

Answer 9

Dlx5 and Dlx6

Question 10

What does the utricle include?

Answer 10

Semicircular ducts and ampullae

Question 11

What is the lateral canal part of?

What gene induces its formation?

Answer 11

Part of the utricle.

Otx1

Question 12

What does the saccule include?

Answer 12

Cochlear duct. ductus reunions, organ of Corti.

Question 13

What are hair cells from?

Answer 13

Otic vesicle –> surface ectoderm

Question 14

Hair cells in the ampullae detect what?

Answer 14

Acceleration

Question 15

Hair cells in the macula of the saccule detect what?

Answer 15

Gravity

Question 16

Hair cells of the organ of Corti detect what?

Answer 16

Sound vibration

Question 17

What innervates the inner ear?

Answer 17

CN VIII.

Vestibular ganglion and spiral (cochlear) ganglion.

Question 18

What is the vestibular ganglion from?

What is the cochlear ganglion from?

Answer 18

Vestibular - NCC

Cochlear - surface ectoderm

Question 19

How can perilymph enter the subarachnoid space?

Answer 19

The perilymphatic duct is usually patent and allows a passageway into the subarachnoid space.

Question 20

How is the ion content of perilymph characterized?

Answer 20

Like CSF.

High Na+, low K+ and protein

Question 21

What produces endolymph?

Where is it stored?

Answer 21

Stria vascularis produces it.

Endolymphatic sac stores it.

Question 22

What is the ion content of endolymph?

Answer 22

Like ICF.

High K+ and protein, low Na+.

Question 23

What forms the bony labyrinth?

Answer 23

Condensation of mesenchyme - mesoderm.

Question 24

How are the semicircular ducts, scala vestibuli and scala tympani formed in the bony labyrinth?

Answer 24

Apoptosis of the cells within the bony labyrinth.

Question 25

Bony labyrinth is from which bone?

Answer 25

Petrous part of temporal bone

Question 26

How is the middle ear formed?

Answer 26

The 1st pharyngeal cleft (ectoderm) formd the ext. auditory meatus meets with the 1st pharyngeal pouch (endoderm).

Question 27

What makes up the tympanic membrane? (3)

Answer 27

Ectoderm, mesoderm, endoderm

Question 28

What makes the ossicles?

Answer 28

NCCs.

Malleus and incus from 1st arch and stapes from 2nd arch.

Question 29

What is tensor tempani m. from?

What is stapedius m. from?

Answer 29

1st pharyngeal arch mesoderm.

2nd pharyngeal arch mesoderm.

Question 30

Rubella infection in 7-8 wks can cause defects in what?

Answer 30

Spiral organ (organ of Corti) and deafness.