Neurulation is the process of the neural tube formation. It begins with appearance of the neural plate, which invaginates along its central axis to form the neural groove, with neural folds on each side. Gradually, the neural folds approach each other in the midline and fuse there, thus converting the neural groove into a neural tube. Formation of the neural tube begins in the region of the future neck (the 4th somite) and proceeds in the cranial and caudal directions. The tube remains temporarily open by way of the cranial (anterior) and caudal (posterior) neuropores. Closure of the anterior neuropore occurs on the 25th day, whereas the posterior neuropore closes on the 27th day.
As the neural tube separates from the surface ectoderm, the neural crest cells migrate to the sides of the neural tube. The neural crest separates into the right and left part, and migrate to dorsolateral aspects of the neural tube, giving rise to the sensory ganglia of the spinal and cranial nerves.

1. Notochord
2. Neural crest
3. Neural fold
4. Surface ectoderm

1. Notochord
2. Neural crest
3. Neural fold
4. Surface ectoderm

1. Notochord
2. Intermediate zone of neural crest
3. Neural tube
4. Surface ectoderm

1. Notochord
2. Dorsal root ganglion
3. Neural tube
4. Surface ectoderm

1. Neural plate
2. Primitive node
3. Primitive streak
4. Cut edge of amnion

1. Neural fold
2. Primitive node
3. Primitive streak
4. Somite
5. Neural groove
6. Cut edge of amnion

1. Pericardial bulge
2. Anterior neuropore
3. Posterior neuropore
4. Somite