(7.1) Special Sense Organs Embryology

Question 1

What is Congenital Rubella Syndrome?

Answer 1

• sensorineural deafness
• congenital cataract/retinopathy
• congenital heart disease e.g. PDA

Question 2

Briefly describe the formation of the inner.

Answer 2

Inner ear:
- Otic placode comes in contact with ectoderm -> invaginate becomes optic vesicle -> cochlear + semicircular canals
Middle ear:
- 1st pharyngeal arch: Meckle’s cartilage -> malleus & incus
- 1st pharyngeal arch: Reichert’s cartilage -> stapes
- 1st pharyngeal pouch -> proximal remains -> Eustachian tube
- 1st pharyngeal pouch -> dismally expands -> tympanic cavity
Outer ear:
- 1st pharyngeal cleft -> external acoustic canal
- Auricular hillocks -> auricles

Question 3

Briefly describe the formation of eyes

Answer 3

1) Diencephalon out pocketing -> optic stalk (distal part = optic vesicle)
2) Neural ectoderm of optic vesicle comes in contact with surface ectoderm -> optic placode
3) Invagination of optic placode pinches off optic vesicle -> lens
4) Remaining optic vesicle cup around lens, leaving a slit, Choroid fissure
5) Choroid fissure encloses Hyloid arteries which grow within it -> arteries degenerate -> central artery of retina
6) Optic vesicle cup -> retina (the invagination creating two layers, outer pigmented + inner neural) -> intraretinal space obliterate
7) Rims of optic cup -> ciliary processes & iris

Question 4

What may be the consequence if intraretinal space fails to obliterate?

Answer 4

Retinal detachment = space between outer pigmented and inner neural layers of retina, although photoreceptors remain, the folded layers impair focusing

Question 5

What may be the consequence if choroid fissure fails to enclose Hyloid arteries?

Answer 5

Coloboma = a hole within an eye structure