L4: Folding and neural tube development

Question 1

What is the definition of neurulation?

Answer 1

formation of neural tube

Question 2

What are the steps of the development of the neural tube?

Answer 2

Neural plate: Thick epiblast above notochord

Neural groove: Median groove at the central axis of the neural plate

Neural fold: 2 folds on each side of the neural groove

Neural tube:
✓ Fusion of neural folds is followed by separation of the neural tube from the epiblast
✓ Cranial & caudal neuropores are at first open then become closed

Question 3

What is the fate of the neural tube?

Answer 3

❖ Cranial part: become dilated to form the brain
❖ Caudal part: forms the spinal cord


Question 4

What are the neural crest cells?

Answer 4

❖ Neuro-ectodermal cells which separate from ectoderm during the fusion neural folds to form the neural tube

Question 5

What are the derivatives of the neural crest cells?

Answer 5

Neuroblasts: which gives rise to all ganglia
• Sympathetic Ganglia
• Dorsal root ganglia

Melanocytes: pigment cells of the skin.

Spongioblasts: which gives:
• Schwan cells
• pia and arachnoids matter

Chromaffin cells: which gives:
• Suprarenal medulla
• Carotid bodies cells.

Odontoblast cells

Question 6

What is the definition of folding?

Answer 6

❖ folding of flat trilaminar embryo ventrally to form a cylindrical embryo.

Question 7

What is the time of folding?

Answer 7

at beginning 4th week.

Question 8

What are the causes of folding?

Answer 8

1) Rapid longitudinal growth of the central nervous system is the cause of head and tail fold.

2) Rapidly growing somites is the cause of lateral folding.

Question 9

What are the results of folding?

Answer 9

Say Rrr….

Shape: ✓ embryo becomes cylindrical.

Amniotic cavity: ✓ enlarge at the expense of yolk sac to surround embryo completely.

Yolk sac: ✓ Divided into two parts:
1) Part inside the embryo form primitive gut (foregut, midgut and hindgut).
2) Part outside embryo becomes definitive yolk sac.

-The duct which connects the midgut with the definitive yolk sac called vitello-intestinal duct

Results of head folding: ✓ Forebrain become the most cranial structure of the embryo.

Results of tail folding: ✓ Cloacal membrane become the most caudal structure of the embryo & Connecting stalk is carried in the anterior surface of the embryo.

Results of lateral folding: ✓ the embryo becomes tubular & the Anterior abdominal wall is formed.

Question 10

What is anencephaly?

Answer 10

• It is a serious birth defect in which a baby is born without parts of the brain and skull.
• It is a type of neural tube defect due to failure of the cranial neuropore to close