Gastrulation and Neurulation

Question 1

Gastrulation

Answer 1

when the two layered disc becomes three

Question 2

sequence

Answer 2

occurs at the start of week three:
epiblast cells stream into the embryo along the primitive streak/node
This begins the formation of the mesoderm and also replaces some hypoblast cells in the endoderm
In front of the node of a specialised mesoderm structure called the notochord forms between the two layers (these are important signalling structure)

Question 3

What forms the notochord and mesoderm

Answer 3

epiblast cells burrow between epiblast and hypoblast to form this and mesoderm

Question 4

Blocking effect

Answer 4

the notochord organises dorsal structures, it releases factors known as:
- chordin
- noggin
- follistatin
These act to block BMP effects and initiate back/neural tissue development

Question 5

Formation of the neural tube

Answer 5

• epithelium become columnar (thicken) forming folds and a groove (day 19)
• day 22: fusion in cervical regions, the edges roll over and the cells fuse to make a tunnel (apical contraction via actin)
• day 27: full closure occurs revealing two ends:
• rostral neuropore (tail)
• caudal neuropore (head)

Question 6

Where do neural crest cells originate from

Answer 6

the neural plate (ectoderm)

Question 7

What is the role of neural crest cells

Answer 7

they undergo epithelial to mesynchmal transition and migrate away from the neural tube epithelium

Question 8

Derivatives of neural crest cells

Answer 8

• cranial nerve ganglia
• dorsal root ganglia
• autonomic ganglia
• adrenal medulla
• Schwann cells
• peripheral glial
• smooth muscle of cardiac out flow
• odontoblasts, cranial facial skeleton
• thyroid parafollicular cells
• melanocytes

Question 9

endoderm derivatives

Answer 9

yolk sac becomes GI tube

buds come off gut tube to form organs

Question 10

ectoderm derivatives

Answer 10

epidermis 
lens and retina 
olfactory epithelium 
oral cavity epithelium 
sensory organs of ear 
glands

Question 11

ectoderm derivatives

Answer 11

epidermis 
lens and retina 
olfactory epithelium 
oral cavity epithelium 
sensory organs of ear 
gland - salivary/sweat/mammary
adenohypophysis

Question 12

ectoderm is formed from

Answer 12

the left over cells in the epiblast (where some have left to replace hypoblast cells in the endoderm)

Question 13

how is the mesoderm formed

Answer 13

from the flow of epiblast cells into the embryo along the primitive streak