3. Neurulation, Segmentation and Folding

Question 1

What is the purpose of neurulation?

Answer 1

1. Forms the neural tube
2. Which will go onto produce the Central Nervous System (brain, spinal cord, meninges and part of bones that surround them)

Question 2

When does neurulation occur?

Answer 2

1. Weeks 3-4

Question 3

What induces neurulation?

Answer 3

1. The notocord
2. Sends signals to the overlying ectoderm

Question 4

What does the notocord later become?

Answer 4

The nucleus pulposus in the middle of intervertebral discs

Question 5

Describe the steps of neurulation

Answer 5

NOTE: step 3 = folding. step 5 = segmentation. haven’t covered it yet but helps with visualising neuralation.

1. Lateral edges of ectoderm become elavated and form the ‘neural fold’. The depressed part of the ectoderm in the middle of the folds = neural groove. Entire thing = neural plate.
2. Neural folds fuse forming neural tube
3. Outer part of ectoderm folds around the mesoderm and endoderm (which makes sense as it will soon become the skin). Results in endoderm becoming smaller (forms lining of GIT and airways), mesoderm becoming larger and in the middle (as it becomes bone, muscle, CT)
4. As neural tube formed, some of its cells migrate to form several layers known as the neural crest (which go onto form PNS, ANS, some meninges). Remaining ectoderm will form the skin
5. Somites form (part of mesoderm). Derivatives eventually = dermatome (skin), myotome (muscles), sclerotome (bones)

Question 6

Here is what the end of the process looks like from a caudal view

Answer 6

Question 7

What is segmentation?

Answer 7

1. Organisation of mesoderm into somites which gives rise to repeating structures such as: vertebrae, ribs, intercostal muscles, spinal cord segments 2. Guides innervation

Question 8

How many somites form spinal nerves?

Answer 8

31 somites = 31 segments = 31 pairs of spinal nerves

Question 9

Describe folding of the embryo

Answer 9

Outer part of ectoderm folds around the mesoderm and endoderm (which makes sense as it will soon become the skin). Results in endoderm becoming smaller (forms lining of GIT and airways), mesoderm becoming larger and in the middle (as it becomes bone, muscle, CT)