Nervous System
Nervous System Development
Development of the nervous system (neurulation) begins in week 3 when the notochord induces the surface ectoderm to form the neural plate. This plate folds to create the neural tube — the precursor to the brain and spinal cord — while neural crest cells emigrate to form the peripheral nervous system.
Week 3 — Neural Plate to Neural Tube
Neurulation
The Notochord induces the overlying ectoderm to thicken into the Neural Plate via BMP inhibition. The neural plate elongates, its lateral edges rise as Neural Folds, which meet and fuse along the dorsal midline.
Fusion starts in the cervical region and proceeds both cranially and caudally. The cranial anterior neuropore closes at day 25 and the caudal posterior neuropore closes at day 27, forming a completely closed Neural Tube. During closure, cells at the junction emigrate as Neural Crest Cells.
Failure of anterior neuropore closure → Anencephaly. Failure of posterior neuropore closure → Spina Bifida. Over 70% of neural tube defects are preventable with adequate Folic Acid intake.