Unit 3: Neurulation

Question 1

What is neurulation ?

Answer 1

The formation of the neural plate and its transformation into a neural tube

Question 2

What is patterning ?

Answer 2

The developmental process by which cells acquire different identities, depending on their relative spatial positions within the embryo

Question 3

What is ‘Fate’ ?

Answer 3

What a cell in a certain location at a certain stage during development is most likely to become at a later stage

Question 4

What is a fate map ?

Answer 4

A plan of an early embryo indicating the potentialities for development and differentiation of the various embryonic areas

Question 5

What germ layer does the nervous system develop from ?

Answer 5

The ectoderm

Question 6

What is the function of the node ?

Answer 6

It induces new axis and neurulation in prospective epidermis

Question 7

What is neural induction ?

Answer 7

The process where certain cells in the early embryo are told to become part of the nervous system, like the brain and spinal cord.

Question 8

What is the default pathway for ectoderm ?

Answer 8

Neural

Question 9

How do you make epidermis ?

Answer 9

• Ectoderm
• LPM (Lateral plate mesoderm)

Question 10

How is neuroectoderm formed (4) ?

Answer 10

1) LPM secretes BMP4 to induce epidermis
2) The notochord secretes noggin (BMP4 antagonist)
3) This allows the default neural pathway to be executed
4) Neuroectoderm is induced directly over notochord

Question 11

How is the neural tube developed from the neural plate (4) ?

Answer 11

1) Neural plate undergoes morphogenetic changes to form neural tube
2) Primary neurulation occurs anterior to the hindlimb
3) Secondary neurulation occurs posterior to the hindlimb

Question 12

What are the 5 steps of primary neurulation ? (Diagram in notes- Slide 21)

Answer 12

1) Initial epithelium
2) Columnarisation
3) Rolling/ Folding
4) Closure
5) Neural tube complete

Question 13

What is neural closure (3) ?

Answer 13

• Zipping of the ectoderm
• Has 5 regions
• Failure to close at spinal chord leads to spina bifida

Question 14

What are the 5 steps of secondary neurulation ?

Answer 14

1) Dispersed mesenchyme
2) Mesenchymal condensation
3) Medullary cord/ neural rod
4) Epithelial transition/ cavitation
5) Neural tube complete

Question 15

When neural plate develops into neural tube, which of the following is required ?
1) Epithelial to mesenchymal transition
2) Presence of noggin
3) Neural crest migration
4) Convergence and extension

Answer 15

4) Convergence and extension

Question 16

Where does primary nucleation occur ?

Answer 16

In the anterior part of the embryo

Question 17

What happens when the neural tube is regionalised (2) ?

Answer 17

• The anterior of neural tube forms the brain
• The posterior of the neural tube forms the spinal chord

Question 18

What genes are important for anterior posterior patterning ?

Answer 18

HOX genes

Question 19

Describe how the neural tube acquires AP patterning ?

Answer 19

• Guided by retanoic acid, FGFs and Wnt
• Signalling molecules create a gradient which helps to establish the brains anterior and posterior regions

Question 20

How does cell division occur in the early neural tube (4) ?

Answer 20

1) Height and area increases but remains 1 cell thick
2) Cells are rapidly dividing- called germinal epithelium
3) When nucleus reaches luminal surface, cytoplasmic connections with outer surface are broken and the cell divides
4) Nuclear oscillations resume

Question 21

How are cell layers formed in the CNS (3) ?

Answer 21

1) Cells that are unable to divide detach from germinal layer and move outward
2) This generates new layer called intermediate/ mantel layer
3) Germinal layer is now called the ventricular layer

Question 22

What are the 2 types of cells the intermediate layer differentiates into ?

Answer 22

1) Neurons
2) Glia

Question 23

What is a neuroblast ?

Answer 23

It is an early-stage, undifferentiated cell in the developing nervous system that is a precursor to a neuron