The document summarizes the process of neurulation during embryonic development. It involves the formation of the neural plate from neuroectodermal cells, which then folds to form the neural groove and neural folds. The neural folds then fuse together beginning in the cervical region, leaving two openings (neuropores) that close sequentially. The fused neural tube will eventually form the brain and spinal cord. Defects in neurulation can result in neural tube defects such as anencephaly, spina bifida, and rachischisis.

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’’