Placodes and Ectoderm Development

Question 1

Define a sensory placode

Answer 1

Thickenings of the surface ectoderm in the head region, give rise to sensory structures like eyes (lens placodes), nose (olfactory placodes), ears (otic placodes), and neurons

Question 2

Which of the 3 subdivisions from the ectoderm can develop neurons?

Answer 2

All 3

1. neural crest
2. surface ectoderm
3. Neural tube

Question 3

Which is the only placode that doesn’t develop neurons?

Answer 3

The lens placode

- The neurons in the eye are from the neural tube

Question 4

How is Shh involved in eye development?

Answer 4

Shh inhibits Pax6 which induces eye formation. Shh is expressed down the midline of the face to create a space between eyes.

Question 5

What does the retina form from?

Answer 5

The optic vesicle

Question 6

What is an otocyst?

Answer 6

Derived from the otic placode, the placode invaginates and makes an indent behind the hindbrain. This gives rise to the inner ear (the cochlea and vestibules - balance)

Question 7

What are all sensory neurons in the dorsal root ganglia derived from?

Answer 7

The neural crest cells

Question 8

What are the distal (in the midline of the brain) ganglia derived from?

Answer 8

placodes

Question 9

What are the cranial sensory ganglia nerves derived from?

Answer 9

Neural crest cells and placodes