Neurulation and the neural crest

Question 1

What is the CNS and what part of the embryo forms it?

Answer 1

• CNS = brain and spinal cord
• formed from the neural tube

Question 2

What is the PNS and what part of the embryo forms it?

Answer 2

• PNS = sensory, enteric, sympathetic and parasympathetic
• formed from the neural crest

Question 3

What does the neural tube form from?

Answer 3

• neural tube forms from the ectodermal layer

Question 4

Where is the neural crest born?

Answer 4

• the neural crest is born in the dorsal part of the neural tube

Question 5

Apart form the neural tube what does the ectoderm also form?

Answer 5

• the epidermis

Question 6

What is the definition of neurulation?

Answer 6

• the process by which the neural tube forms from the ectodermal layer

Question 7

How does the ectoderm from?

Answer 7

• formed from the cells that remain in the epiblast during gastrulation

Question 8

What are the 4 basic steps of neurulation?

Answer 8

1. shaping and folding (sleep)
2. elevation (eat)
3. convergence (cook)
4. closure (chicken)

Question 9

What happens during stage 1 - shaping and folding?

Answer 9

• shaping - the ectoderm layer thickens towards the edge by changes in shape of cells
• folding - cells along the midline form a hinge (median hinge point MHP) by attaching to the notochord
• the plate is now called the neural groove

Question 10

What happens at stage 2 - elevation?

Answer 10

• ectoderm on either side of the neural groove pushes towards the centre causing the centre to deepen and edges to lift up

Question 11

What happens at stage 3 - convergence?

Answer 11

• the dorsolateral hinge point (DLHP) forms which makes the neural groove bend at the top

Question 12

What happens at stage 4 - closure?

Answer 12

• the edge of the neural tube fuse
• the ectoderm grows over the top
• once the tube is fully closed a layer of tissue fully grows over the top, that layer is now called the epidermis

Question 13

Closure of the neural tube is initiated in how many different places?

Answer 13

• 5 different places so not craniocaudal progression

Question 14

What happens if there is failure to close caudal neural tube?

Answer 14

• spina bifida

Question 15

What happens if there is failure to close the cranial neural tube?

Answer 15

• exencephaly

Question 16

Why is folic acid important during embryonic development?

Answer 16

• a lack of folic acid will cause incomplete and incorrect closure of the neural tube

Question 17

what results from primary neurulation?

Answer 17

• the cranial neural tube is formed
• the neural plate elevated then folds to from tube
• only occurs down to lumbar level

Question 18

How are the sacral/caudal regions formed?

Answer 18

• formed by secondary neurulation

Question 19

How is the medullary chord formed?

Answer 19

• medullary chord formed when mesenchymal cells form a solid rod
• mesenchymal cells = stem cells that form from the mesoderm

Question 20

How does a lumen from in the medullary chord?

Answer 20

• numerous cavities within the medullary chord eventually fuse together to from one lumen known as cavitation

Question 21

Where do the neural crest cells originate from?

Answer 21

• originate at the junction of the epidermis and neural plate - crest neuroectoderm

Question 22

What does the neural plate closure do?

Answer 22

• brings the epidermis in contact with the crest neuroectoderm

Question 23

What happens when the epidermis contacts the crest neuroectoderm?

Answer 23

• this induces an epithelial to mesenchymal transition within the crest neuroectoderm

Question 24

what forms the neural crest?

Answer 24

• neural plate cells that break away from the neural pate

Question 25

How does the neural crest migrate?

Answer 25

• migrates along defined pathways away from neural tube

Question 26

What are the neural crest derivatives?

Answer 26

• PNS
• pigment cells
• bone, cartilage, and connective tissue - only in the head

Question 27

What is the sympathetic/parasympathetic system?

Answer 27

• both part of the ANS
• flow of information from the CNS to the periphery
• control gut motility, blood vessel diameter, bladder control, energy release/storage (glucose)
• basis of fight or flight / rest and digest responses
• sympathetic uses energy
• parasympathetic - conserves energy

Question 28

What is the sensory nervous system?

Answer 28

• sensory neurons “sense” the environment and send info via the spinal cord
• flow of information from the periphery to CNS

Question 29

What are the advantages to the peripheral nervous system?

Answer 29

• can detect changes in the environment
• can detect if being attacked
• can respond to changes and attack swiftly and in co-ordinated manner