Lecture 15: Ear Development

Question 1

When is the critical period for embryological development of the ear?

Answer 1

Weeks 4-8

Question 2

When does development of the ear occur?

Answer 2

Week 4-20

Question 3

What is found in the external, middle, and inner ear?

Answer 3

External Ear

• Auricle
• External Acoustic Meatus
• External Layer of Tympanic Membrane

Middle Ear

• Auditory Ossicles (3)
• Internal Layer of Tympanic Membrane
• Middle Ear Cavity

Inner Ear

• Vestibulocochlear Organ
• Develops separately from external and internal ear

Question 4

The medial part of the external ear came from what pharyngeal arch?

Answer 4

1^st Pharyngeal Arch

Question 5

The lateral part of the external ear came from what pharyngeal arch?

Answer 5

2^nd Pharyngeal Arch

Question 6

The mesenchymal swellings located within the pharyngeal arches are known as what?

Answer 6

Auricular Hillocks

Question 7

What are the cells that migrate and pull the surface ectoderm around to form the external ear?

Answer 7

Neural crest cells of the auricular hillocks

Question 8

Auricular skin tags that may contain cartilage are a result of what?

Answer 8

Abnormal migration of surface ectoderm and neural crest cells

Question 9

Abnormal or absent migration of the NCCs and auricular hillocks can result in what disorders?

Answer 9

Anotia

Microtia

Question 10

What embryonic layer does the meatal plug arise from?

Answer 10

Surface ectoderm

1^st Pharyngeal Cleft

Question 11

What embryonic layer forms the tubotympanic recess?

Answer 11

Endoderm: 1^st Pharyngeal Pouch

Question 12

What embryonic layer does the inner ear arise from?

Answer 12

Surface ectoderm

Question 13

How does the inner ear form from surface ectoderm?

Answer 13

1. Otic Placode thickens
2. Invaginates to form Otic Pit
3. Becomes Otic Vesicle that migrates to the head

Question 14

What embryonic structure gives rise to the membranous labyrinth?

Answer 14

Otic vesicle

Also Surface Ectoderm

Question 15

What does the dorsal side of the otocyst give rise to?

Answer 15

Utricle

1. Endolymphatic duct and sac
2. Semicircular ducts and ampullae
3. Macula of utricle

Question 16

What does the ventral side of the otocyst give rise to?

Answer 16

Saccule

1. Cochlear duct
2. Ductus reuniens
3. Maccula of saccule
4. Organ of Corti

Question 17

What structure connects the cochlea to the vestibular apparatus?

Answer 17

Ductus reunions

Question 18

What is the embryonic layer that gives rise to the hair cells of the inner ear?

Answer 18

Surface ectoderm

Question 19

Where are hair cells located in the inner ear?

What does the respective hair cells sense?

Answer 19

• Ampullae of Semicircular Canals
  
  • Rotational Acceleration
• Macula of utricle and saccule
  
  • Linear Acceleration
• Organ of Corti (cochlea)
  
  • Sound Vibration

Question 20

What nerve is responsible for innervation to the inner ear?

Where did this nerve come from?

Answer 20

CN VIII: Vestibulocochlear Nerve

Otic Placode

Question 21

What are the embryonic contributions to the vestibular ganglion?

What cell bodies contribute to this?

Answer 21

Neural crest cells and surface ectoderm

Cell bodies from macula and ampullae

Question 22

What is the embryonic contribution to the spiral (cochlear ganglion)?

Answer 22

Surface ectoderm

Question 23

What structures does the perilymphatic duct provide passage between?

Answer 23

Subarachnoid space to inner ear

Question 24

What is the ion content of perilymph?

Answer 24

High Na⁺

Low K⁺ and Protein

(Similar to CSF)

Question 25

What is the ion content of endolymph?

Answer 25

High K⁺ and Protien Low Na⁺ (Similar to ICF)

Question 26

What produces endolymph?

Answer 26

Stria Vascularis

Question 27

What embryonic layer does the bony labyrinth arise from?

Answer 27

Mesoderm ## Footnote *Condensation of Mesenchyme*

Question 28

What are the vacuoles of the bony labyrinth?

Answer 28

Scala Vestibuli Scala Tympani Semicircular Ducts (Perilymphatic Space)

Question 29

What suspends the cochlear duct within the bony labyrinth and attaches it to the wall?

Answer 29

Spiral Ligament

Question 30

What bones of the middle ear arise from the 1^st pharyngeal arch? What is their embryonic origin?

Answer 30

Malleus and Incus Neural Crest Cells

Question 31

The stapes bone arises from what arch? What is the embryonic origin?

Answer 31

2^nd Pharyngeal Arch Neural crest cells

Question 32

What embryonic layer does the epithelium covering the ossicles arise from?

Answer 32

Endoderm

Question 33

What are the embryonic layers making up the tympanic membrane?

Answer 33

Arive from 1^st Pharyngeal Membrane * Ectoderm: from 1^st Pharyngeal Cleft * Mesoderm * Endoderm: from 1^st Pharyngeal Pouch

Question 34

What pharyngeal arch does the Tensor Tympani Muslce arise from? What embryonic layer? What innervates this muscle?

Answer 34

1^st Pharyngeal arch Mesoderm CN V₃

Question 35

What pharyngeal arch does the Stapedius Muslce arise from? What embryonic layer? What nerve innervates it?

Answer 35

2^nd Pharyngeal Arch Mesoderm CN VII

Question 36

What part of the fetal ear is affected if there is a maternal Rubella infection?

Answer 36

Inner ear: Spiral Organ/Organ of Corti defects

Question 37

What is the leading cause of congenital sensorineural hearing losss?

Answer 37

Cytomegalovirus