Failure to form
The nervous system forms in a specific sequence.
A neural groove (nerve
cells)forms in a line somewhat like a ditch, gets deeper and begins to close over on itself. It closes from the center outward in both directions.If the top doesn't close, the skull doesn't finish to cover the brain
,which is exposed.If the bottom doesn't close, you have spina bifida
. Both are sporadic malformations.