Development of Ear

Question 1

What are the functions of the inner ear?

Answer 1

conversion of sound waves into nerve impulses and regulation of changes in equilibrium

Question 2

What is the function of the middle ear?

Answer 2

sound conduction

Question 3

Function of outer ear

Answer 3

sound collection

Question 4

What is a placode made of?

Answer 4

ectodermal thickening

Question 5

How does the cochlear duct maintain contact with saccule?

Answer 5

ductus reuniens

Question 6

What separates scala vestibuli from cochlea? Scala tympani?

Answer 6

• vestibular membrane

- basilar membrane

Question 7

What attaches the lateral wall of cochlear duct to cartilage?

Answer 7

spiral ligament (periosteum)

Question 8

What supports the medial angle of the cochlear duct?

Answer 8

modiolus

Question 9

Two ridges formed from cochlear epithelial cells

Answer 9

inner = spiral limbus
outer = inner and outer hair cells

Question 10

What covers cochlear epithelial cells?

Answer 10

tectorial membrane attached to spiral limbus

Question 11

What gives rise to semicircular canals (balance)?

Answer 11

outpocketing of utricular part of otic vesicle

Question 12

What are the 3 types of semicircular canals? 5 crura?

Answer 12

• dilated end = crus ampullae
  non-dilated end = crus nonampullare
• 3 with ampulla
  2 without

Question 13

What do the cells within the ampullae form?

Answer 13

crest termed crista ampullaris

- sensory cells responsible for equilibrium

Question 14

What occurs during otic development?

Answer 14

small group of cells forms the statoacoustic ganglion

Question 15

What is tee statoacoustic ganglion derived from?

Answer 15

neural crest cells and ectoderm

Question 16

What does the statoacoustic ganglion split into?

Answer 16

cochlear (spiral) and vestibular portions

- supports organ of corti, saccule, utricle, and semicircular canals

Question 17

What does the distal part of the 1st pharyngeal pouch become?

Answer 17

tubotympanic recess giving rise to primordial cavity

Question 18

What does the proximal part of 1st pharyngeal pouch become?

Answer 18

auditory tube (connection to nasopharynx)

Question 19

Where is the tympanic cavity derived?

Answer 19

1st pharyngeal pouch

Question 20

What is the primordial TMJ?

Answer 20

malleus and incus until upper portion of ramus develops

Question 21

How does tympanic antrum form? When?

Answer 21

vacuolization (creation of empty space)

- late fetal life

Question 22

What occurs after birth in middle ear?

Answer 22

tympanic cavity invades mastoid process causing pneumatization

Question 23

What happens when external ear epithelial cells undergo rampant proliferation?

Answer 23

formation of meatal plug

Question 24

What forms the eardrum?

Answer 24

meatal plug dissolving around 7 months

Question 25

What does the eardrum attach to?

Answer 25

malleus

- eardrum acts to separate external auditory meatus and tympanic membrane

Question 26

How many mesenchymal proliferations form auricle?

Answer 26

6

Question 27

What forms the auricle?

Answer 27

1st and 2nd pharyngeal arches surrounding 1st pharyngeal cleft

Question 28

Clinical presentation of auricular atresia or microtia

Answer 28

• underdeveloped pinna (unilateral or bilateral and variable)
• hearing impairment

Question 29

pathogenesis of microtia

Answer 29

• teratogen (accurate, thalidomide, retinoid acid)

- decreased blood supply

Question 30

Why is the lobule almost never missing?

Answer 30

2nd arch derivative instead of 1st arch abnormality which is common