Week 3 - Ach (Embryo of Eye & Ear)

Question 1

When does the otic placode appear?

Answer 1

around Day 22

Question 2

What are the general derivatives of the otic placode?

Answer 2

• ​Inner Ear
  
  • Otic Vesicle => MEMBRANOUS Labyrinth
    
    • Utricle –> Semicircular Duct
    • Saccule –> Cochlear Duct
  • ​Otic Capsule => BONY Labyrinth
    
    • Semicircular Canals
    • Cochlea
    • Vestibule

Question 3

What area of the primitive brain do the otic placodes arise?

Answer 3

Mylencephalon

Question 4

What dermal layer thickens to form the otic placodes?

Answer 4

Ectoderm

Question 5

How do the otic vesicles form?

Answer 5

• Otic pits invaginate in each otic placode
• Otic pits sink into underlying mesoderm and detach from the surface ectoderm

Question 6

What does each otic vesicle form?

Answer 6

• Epithelial structures of the inner ear
  
  • Membranous labyrinth
    
    • Dorsal part
      
      • Utricles
      • Semicircular Ducts
      • Endolymphatic duct
    • Ventral part
      
      • Saccules
      • Cochlear Ducts
      • Ductus reuniens

Question 7

How does the bony (osseous) labyrinth form?

Answer 7

Mesoderm surrounding otic vessicle –>

condenses into cartilaginous otic capsule –>

becomes bony labyrinth via endochondral ossification

Question 8

What is the Statoacoustic Ganglion formed by?

Answer 8

Cells from the wall of the otic vesicle and neural crest cells.

Question 9

What do the tympanic cavity and Eustachian tube form from?

Answer 9

Endodermal origin from 1st pharyngeal pouch

(tubotympanic recess)

Question 10

What cartilage do the ossicles form from?

Answer 10

Malleus and Incus –> dorsal tip of 1st pharyngeal arch (Meckel’s cartilage)

Stapes –> 2nd pharyngeal arch (Reichert’s cartilage)

Question 11

What middle ear muscle/nerve derives from the 1st pharyngeal arch?

Answer 11

Tensor tympani - CN V3

Question 12

What middle ear muscle/nerve derives from the 2nd pharyngeal arch?

Answer 12

Stapedius - CN VII

Question 13

The external ear is derived from what pharyngeal cleft derivative?

Answer 13

1st

Question 14

What are the three embryologic layers of the Tympanic Membrane?

Answer 14

1. Ectodermal outer layer - 1st pharyngeal groove
2. Mesodermal middle layer - 1st & 2nd pharyngeal
3. Endodermal inner layer - 1st pharyngeal

Question 15

What embryological processes can cause neurosensory deafness?

Answer 15

• Abnormal development of:
  
  • cochlea
  • CN VIII
  • brainstem
• Rubella in 1st trimester
• Neural crest deficit (essential in stria vascularis)

Question 16

What embryological processes can cause conduction deafness?

Answer 16

• Persistance of meatal plug
• Fixation of footplate of stapes
  
  • annular ligament failure
• Abnormalities of malleus and incus

Question 17

Describe the development of the optic cup from the diencephalon.

Answer 17

1. Neuroectoderm of the Diencephalon
2. Optic grooves
3. Optic vesicles
4. Optic Cup

Question 18

What are the 8 basic derivatives of the optic cup?

Answer 18

1. Retina
2. Iris
3. Lens
4. Vitreous/Aqueous humor
5. Choroid/Sclera
6. Cornea
7. Conjunctiva
8. Eyelids

Question 19

The optic nerve is a tract of what?

Answer 19

the Diencephalon

Question 20

Hyaloid vessels are branches of what? What do they supply?

Answer 20

Branches of the Ophthalmic Vessels

Supply:

• Optic Nerve
• Retina
• Posterior aspect of the Lens Capsule

Question 21

What process inolving the optic nerve continues after birth?

Answer 21

Myelination

Question 22

When does the Hyaloid artery normally regress?

Answer 22

11 weeks - 8 months

Question 23

What is a congenital coloboma?

Answer 23

Defective closure of the choroid or optic fissure.

Question 24

Where is a Congenital Coloboma positioned?

Answer 24

infero-nasal quadrant

(reflective of the location of the optic fissure during fetal development)

Question 25

What two layers of the optic cup become the retina? What do each become?

Answer 25

• Thin outer layer
  
  • Retinal pigmented epithelium (RPE)
• Thick inner neural layer
  
  • Photoreceptors
  • Bipolar/Ganglion cell layers

(layers separated by Intraretinal Space that disappears around week 6)

Question 26

What may a congenital detached retina be due to?

Answer 26

The failure of the retinal layers to fuse and obliterate the intraretinal space.

(or by unequal growth of the eye)

Question 27

What is Microphthalmia?

Answer 27

Arrested development of the optic vesicle

(globe is small & lens does not form)

Question 28

What is Anophthalmia?

Answer 28

Arrested development of the optic vesicle early in Week 4.

Usually accompanies severe craniocerebral defects.

Question 29

What causes congenital glaucoma?

Answer 29

Malformed drainage apparatus

or

Rubella

Question 30

What embryological tissue is the lens derived from?

Answer 30

Ectoderm