L9 Gastrulation and Neurulation

Question 1

What is gastrulation?

Answer 1

The process of forming three distinct germ layers from the inner cell mass of a blastocyst

• Ectoderm
• Mesoderm
• Endoderm

Question 2

What are the stages (in order) of gastrulation?

Answer 2

1. Initiation by ‘organiser’
2. Formation of primitive streak and node in epiblast
3. Posterior extension of streak
4. Migration of epiblast cells through node to form endoderm
5. Migration of epiblast cells through streak to form ventral and lateral mesoderm
6. Regression of streak & replacement by notochord

Question 3

What is neurulation?

Answer 3

The process of forming the neural tube, which will eventually give rise to the spinal cord and brain.

Question 4

What are the stages of neurulation (in order)?

Answer 4

1. Organisers in mesodermal tissue signal formation of neural plate in ectoderm
2. The neural plate folds, the centre descends while the edges peak
3. Edges fold in and fuse forming a tube
4. The tube separates as it sinks down away from the ectoderm into the mesoderm
   5.

Question 5

What are neural crest cells?

Answer 5

Clusters of future neural cells that form dorso-laterally to the neural tube. They will become nerves and pigment cells in the future.

Question 6

What is the result of failed neurulation (the folds don’t completely fuse to form the neural tube)?

Answer 6

Conditions such as spina bifida and anencephaly

Question 7

From which germ layer does the neural tube form?

Answer 7

Ectoderm