Neuralation

Question 1

What structures form that become the neural tube and how?

And when is neural tube formation complete?

Answer 1

1. Neural Plate (AKA neuroectoderm) - notochord induces ectoderm to thicken (cranial to prim. node > OP membrane) into this via TGFB
2. **Neural Groove **forms via invagination of plate
3. Neural Folds on either side of groove stick up, more prominent at cranial end

• the folds move together and fuse over the groove to form the neural tube by the end of week 3

Question 2

Describe the formation of the neural crest and what it becomes within the mesoderm.

Answer 2

1. Crests of each neural fold de-epithelialize (EMT?) and detach
2. These neural crest cells migrate to form flattened mass, the neural crest, over the neural tube
3. The neural crest then splits in two and migrates to either side of the neural tube to form the primordia of the sensory ganglia of cranial/spinal nerves

Question 3

What are some of the derivatives of neural crest cells?

Answer 3

1. dorsal root ganglia
2. CN V, VII, IX, X ganglia
3. peripheral neurilemmae
4. meninges
5. pigment cells
6. adrenal medulla
7. skeletal/muscle components of head

D C N M P A H

Question 4

What is secondary neuralation?

Answer 4

neuroectoderm and endoderm form the conus medullaris

• cone shaped end of spinal cord just above the cauda equina

Question 5

What 5 things form in the cranial ectoderm as the neural tube closes?

What do they become?

Answer 5

Placodes

• symmetrical thickenings of ectoderm
• OL HOT

1. Otic - epi cells of hearing, vestibular apparatus, assoc. ganglia
2. **Lens **- eye lens
3. **Hypophysis **- Rathke pouch > adenohyphophysis
4. **Olfactory **- olfactory epi. + GNRH secretors
5. **Trigeminal **- neurons + glia of trigem ganglion

Question 6

What are the openings at either end of the embryo formed during neural tube formation?

When do they close?

Answer 6

neuropores

cranial - day 25

caudal - day 27

Question 7

What morphogenetic factors induce some of neuralation?

Via what genes?

Answer 7

retinol

Wnt gene products

induce Homeobox (HOX) genes