somites

2. Neurulation
• Formation of the
neural tube
• Inductive factors:
– Inactivation of BMP by
chordin, noggin &
follistatin
• produced by notochord &
primitive node
– Expression of WNT-3A
&FGF; & production of
retinoic acid
• (WNT-3A = wingless-type
MMTV integration site
family, member 3A) 2

3. – formation of neural
plate
• Begins in week 3
• From neuro-
ectodermal cells
• On the dorsum of the
embryo, cranial to
primitive node

4. • Formation of neural
folds & neural groove
• Formation of the neural
crest
4

5. • Formation of the neural tube
– Forms as neural folds touch and
fuse
• beginning in the cervical region (level of
5th somites)
– Two neuropores are then formed:
• Rostral (anterior) neuropore
• Caudal (posterior) neuropore
5

6. • Fusion of the neural folds progress
craniocaudally, leaving two
neuropores:
– Cranial neuropore
• closes by 25th day (18-20 somite stage)
– Caudal neuropore
• closes by 27th day (25 somite stage)

7. Summary:
Stages in
neural tube
formation

8. Derivatives of the neural tube
• Cranial ⅔ forms the brain vesicles
• Caudal ⅓ forms the spinal cord
8

9. Clinical correlates of neurulation
• Neural tube defects
– Anencephaly (with cranioschisis)
– Cranial meningocoele
– Meningoencephalocoele
– Meningohydroencephalocoele
– Spina bifida:
• spina bifida occulta
• spina bifida cystica:
– Meningocoele
– Meningomyelocoele
• Rachischisis (myeloschisis)
9

10. Cranial meningocoele

11. Anencephaly:
associated with cranioschisis

12. Spina bifida occulta

13. Spina bifida with
meningocoele

14. Spina bifida with meningomyelocoele

15. Rachischisis

16. Formation of somites
• See ‘’Period of Organogenesis’’