Ear Development

Question 1

What structures are a part of the external ear?

Answer 1

Auricle (pinna), external acoustic meatus, external layer of tympanic membrane

Question 2

What structures are a part of the middle ear?

Answer 2

The three ossicles, the internal layer of the tympanic membrane, middle ear cavity

Question 3

What structures are a part of the inner ear?

Answer 3

Vestibulocochlear organ

Question 4

What is the auricle derived from?

Answer 4

1st and 2nd pharyngeal arches. Auricular hillocks (NCC) covered in surface ectoderm. Migrate and proliferate to make shape of outer ear

Question 5

What are auricular appendages/skin tags?

Answer 5

Hillocks did not migrate properly, may or may not contain cartilage (NCC)

Question 6

What is anotia?

Answer 6

No external ear due to abnormal migration/proliferation of NCC

Question 7

What is microtia?

Answer 7

Small external ear, due to abnormal migration/proliferation of NCC

Question 8

What is the meatal plug?

Answer 8

Comes from the 1st pharyngeal cleft/groove. Migrates in to meet up with the pouch, proliferation of surface ectoderm. Supposed to undergo apoptosis to create external auditory meatus

Question 9

When does the inner ear form? What is it derived from?

Answer 9

Week 4, surface ectoderm

Question 10

How does the inner ear form?

Answer 10

Thickening of surface ectoderm makes the otic placode which invaginates to make the otic pit. The pit rounds up to make the otic vesicle which migrates deeper into the head.
Gives rise to the primordium of the membranous labyrinth

Question 11

What layer does the membranous labyrinth come from?

Answer 11

Surface ectoderm

Question 12

What is the membranous labyrinth divided into?

Answer 12

The utricle (dorsal) and saccule (ventral)

Question 13

What does the utricle give rise to?

Answer 13

Endolymphatic duct/sac, semicircular ducts and ampullae, and macula of utricle

Question 14

What does the saccule give rise to?

Answer 14

Cochlear duct, ductus reunions, macula of saccule, organ of corti

Question 15

What parts of the membranous labyrinth contain hair cells?

Answer 15

ampullae of semicircular ducts, macula of utricle, macula of saccule, organ of corti

Question 16

What does the ampullae detect?

Answer 16

Rotational acceleration

Question 17

What does the macula detect?

Answer 17

Gravity and linear acceleration

Question 18

What does the organ of corti detect?

Answer 18

Sound vibration

Question 19

What layer do the hair cells come from?

Answer 19

Surface ectoderm

Question 20

What innervates the inner ear? What layer did it come from?

Answer 20

Vestibulocochlear nerve (CN VIII), surface ectoderm

Question 21

What nerve do the cells of the spiral ganglion of the cochlea form?

Answer 21

Cochlear N

Question 22

What nerve do the cells of the vestibular ganglion of the cochlea form?

Answer 22

Vestibular N

Question 23

What is perilymph?

Answer 23

Similar to CSF (high NA, low K and protein), comes from periosteum

Question 24

What is endolymph?

Answer 24

Similar to intracellular fluid (high K and protein, low NA), comes from stria vascularis, stored in endolymphatic sac

Question 25

What fills the structures (ducts) of the membranous labyrinth?

Answer 25

Endolymph

Question 26

What fills the space (canals) between the membranous labyrinth and the bone?

Answer 26

Perilymph

Question 27

How can a chronic middle ear infection get dangerous?

Answer 27

If the infection erodes into the perilymph it can get into the subarachnoid space through the perilymphatic duct

Question 28

Where is the bony labyrinth located? What layer is it from?

Answer 28

Petrous part of temporal bone, condensation of mesenchyme (mesoderm)

Question 29

Where do ossicles come from?

Answer 29

NCC-derived, covered in endoderm

Question 30

What muscle inserts onto the malleus and prevents loud sound from damaging ear? What is it innervated by?

Answer 30

Tensor tympani, trigeminal n (first arch mesoderm)

Question 31

What muscle inserts on the stapes and prevents damage from loud sound? What is it innervated by?

Answer 31

Stapedius m, facial n (second arch mesoderm)

Question 32

What causes congenital deafness?

Answer 32

Maldevelopment of sound-conduction apparatus in middle/external ears (ex: ossicles), neurosensory sensory structures of inner ear, infections