Development of the Ear

Question 1

What is contained in the external ear?

Answer 1

Auricle (pinna)
External acoustic meatus
External layer of the tympanic mebrane

Question 2

What is contained in the middle ear?

Answer 2

Ossicles
Internal layer of tympanic membrane
Middle ear cavity

Question 3

What is contained in the internal ear?

Answer 3

Vestibulocochlear

develops independently of external and middle

Question 4

Where is the auricle derived from? What are the auricular hillocks made of? How does it form?

Answer 4

1st and 2nd pharyngeal arches

Mesenchyme (NCC) swellings covered with surface ectoderm

NCC migrate and proliferate to form shape of ear

Question 5

What innervates the external ear?

Answer 5

Great Auricular n.
CN V3: auriculotmeproal (arch 1)
CN VII (arch 2)
CN X auricular branches

Question 6

What can cause external ear defects?

Answer 6

If have skin tags with just skin no cartilage= surface ectoderm issue

Everything else aka anotia and microtia is abnormal migration of NCC

Question 7

Where does the external auditory meatus come from? How does this occur?

Answer 7

First pahryngeal cleft/groove (ectoderm)

Groove migrates up and meets pouch –> proliferation of surface extoderm –> meatal plug –> external acoustic meatus

Question 8

What is the inner ear derived from? How does this process occur?

Answer 8

Surface ectoderm

Otic placode (thickening of ectoderm) invaginates –> otic plate which migrates –> otic vesicle which migrates into head as mandibular prominence grows

All of these structures lead to the formation of the primordium of membranous labyrinth

Question 9

What structures come from the dorsal/utricle portion of the membranous labyrinth? What layer are they from?

Answer 9

Endolymphatic duct and sac
Semicircular ducts and ampullae –> lateral canal
Macula of utricle

Surface ectoderm

Question 10

What structures arise from the saccule/ ventral portion of the membranous labyrinth? What layer are they from?

Answer 10

Cochlear duct
Ductus reunions
Macula of saccule, organ of Corti

surface ectoderm

Question 11

What do hair cells of the ampullae sense?

Answer 11

rotational acceleration

Question 12

What do hair cells of the macula sense?

Answer 12

Gravity and linear acceleration

Question 13

What do hair cells of the organ of corti sense?

Answer 13

Sound vibration

Question 14

What innervates the inner ear?

Answer 14

Cranial nerve VIII which has vestibular ganglion for macula and ampullae and spiral cochlear ganglion

Question 15

Where is perilymph found? Where can it travel to? What is its ion concentration similar to?

Answer 15

From periosteum between membranous labyrinth and bone

Into the subarachnoid space via the perilymphatic duct

Question 16

Where is endolymph found? What is it produced by? Where is it stored? What is it similar in ion concentration to?

Answer 16

Fills membranous labyrinth duct structures

stria vascularis

endolymphatic sacs

intracellular fluid

Question 17

Why is perilymph clinically significant?

Answer 17

If get ear infection in middle ear can erode spread the infection to perilymph –> infection of subarachnoid space –> meningitis

Question 18

What is the bony labyrinth?

Answer 18

Condensation of mesenchyme

Ossifies and becomes petrous part of the temporal bone

Question 19

How do the vacules develop?

Answer 19

Cochlear duct surrounded by cartilaginous otic capsule –> apoptosis cause development of vacules in perilymphatic space and development of organ of corti –> bony cochlea with scala vestibuli, scala tympani, cochlear duct with organ of corti, and spiral ganglion

Question 20

What is contained in the scala vestibuli and scala tympani? What are these structures derived from?

Answer 20

perilymph

mesenchyme

Question 21

What is contained in the cochlear duct aka scleramedia? What is this structure derived from?

Answer 21

Enodlymph
Also has organ of corti sitting inside

ectoderm

Question 22

What forms the external auditory meatus?

Answer 22

1st pharyngeal cleft (ectoderm)

Question 23

What forms the tympanic recess?

Answer 23

1st pharyngeal puch (endoderm)

Question 24

What forms the tympanic membrane?

Answer 24

1st Pouch and groove meet up= ecto endo and mesoderm

Question 25

What does the malleus and incus form from?

Answer 25

1st arch NCCs (bones are neural crest but covered with endoderm epithelium)

Question 26

What does the stapes form from?

Answer 26

2nd arch NCCs (bones are neural crest but covered with endoderm epithelium)

Question 27

Where does the tensor tympani come from? What is its action?

Answer 27

1st pharyngeal arch mesoderm so innervated by trigeminal

prevents damage from loud sounds, inserts into handle of the malleus

Question 28

Where does the stapedius come from?

Answer 28

2nd pharyngeal arch mesoderm so innervated by facial n.

prevent damage from loud sounds by pulling the stapes posteriorly and tilting its base in the oval window

Question 29

What can cause maldevelopment of sound sound conduction?

Answer 29

Issue with apparatus of middle and external ear

Causes:

• 1st arch syndrome
• Abnormalities in mallus and incus (first arch)
• congenital fixation of stapes (2nd arch)

Question 30

What infections can cause issues in the inner ear?

Answer 30

Rubella (during week 7-8) cause defects of spiral organ and deafness, sensorineural
Cytomegalovirus –> sensorineural hearing loss
Toxoplasmosis
Syphilis
Zika

Question 31

What can toxoplasma gondia cause? Treponema pallidum?

Answer 31

hearing loss

congenital deafness