Inner Ear Embryology

Question 1

List the very beginning inner ear structures in order (start with otic placode

Answer 1

Otic placode (ectoderm thickens and folds inward –> Otic pit –> Otic vessicle/Otocyst (fluid filled sac) –> Otic capsule (Mesenchyme surrounds otocyst)

Question 2

What structure do all inner ear structures form from?

Answer 2

Otocyst

Question 3

List the 3 stages of development of the Otic capsule (bony labyrinth) in order

Answer 3

1: Chondrification
2: Peri-lymphatic (peri-otic) sac forms
3: Ossification

Question 4

Where does the organ of Corti form from and when does it begin?

Answer 4

Ventral Otocyst, begins 9-10 fetal weeks

Question 5

List the developmental gradients in the cochlea

Answer 5

1. Base to Apex

2. Inner to Outer

Question 6

What is the Sliding Place Principle?

Answer 6

Change in place of responsiveness. The base initially responds to low frequencies, mature base responds to high frequencies.

Question 7

When is there an adult # of hair cells?

Answer 7

22 Fetal wks

Question 8

Which hair cells are chaotic and uneven during initial development?

Answer 8

OHCs

Question 9

During stereociliogenesis, when do IHCs have adult configuration & U-Shaped?

Answer 9

12-13 fetal wks

Question 10

When are the stereocilia adult-like on both IHCs and OHCs?

Answer 10

20-21st fetal wks

Question 11

When is the stria vascularis mature by?

Answer 11

19 fetal wks

Question 12

Cochlear nerve fibers: Type I innervate _____

Type II innervate ________

Answer 12

Type I : IHCs

Type II: OHCs

Question 13

When does the space between the tectorial membrane major and minor form?

Answer 13

~18 weeks

Question 14

Describe Michel’s Aplasia

Answer 14

Complete failure of inner ear development. Absent cochlea, vestibule, SCC & likely the nerve. Problem with Otic placode formation

Question 15

Cochlear aplasia

Answer 15

Absent cochlea, vestibule & SCC present

Question 16

Common cavity

Answer 16

Cochlea and vestibule in a common cavity

Question 17

Incomplete Partition I

Answer 17

No bony modiolus & no interscalar septum

Question 18

Incomplete Partition II (Mondini Dysplasia)

Answer 18

1.5 cochlear turns instead of 2.5-2.75

Question 19

Cochlear Hypoplasia

Answer 19

Underdeveloped cochlea

Question 20

Hair cell innervation: Penetration starts when?

Answer 20

Week 11 GA

Question 21

Hair cell innervation: Fibers contact OHCs

Answer 21

Week 14 GA

Question 22

Name 2 syndromes that cause abnormalities of the 1st pharyngeal arch

Answer 22

1. Treacher Collins

2. Pierre Robin

Question 23

When are hair cells differentiated by?

Answer 23

10-11 wks

Question 24

When does a fetus reasonably respond to sound by?

Answer 24

25 fetal wks

Question 25

Where do spiral ganglia develop from?

Answer 25

Otic Vessicle

Question 26

When is the cochlea mature by?

Answer 26

25 wks

Question 27

When does the cochlea have 2 3/4 turns developed?

Answer 27

10-11 wks