Neurulation

Neurulation is the process where components of the post-gastrulation embryo transform to create the future nervous system.

Following gastrulation, surface ectoderm at the embryos periphery is destined to generate skin components whereas more centrally located tissue, the neural ectoderm will produce the spinal cord and brain.

Protein signals cause this midline ectoderm to thicken and form the neural plate beneath which is a condensed rod of mesodermal cells known as the notochord. The center of the plate then affixes to this underlying structure.

Initially, notochord attached cells resemble columns. However, over time, they can tort into wedges, which, along with other factors causes the entire neural plate to bend upwards and inwards as if on a hinge. Concurrently, the plates edges become more prominent, generating structures called neural folds.

Eventually, two additional hinges arise. One beneath each neural fold and both fastened to the surface ectoderm causing the plates edges to turn inwards. 

During this process of primary neurulation, the neural folds continue to move towards one another and ultimately touch, core less and detach from the embedding surface ectoderm. The result is a hollow ectoderm derived cylinder named the neural tube, which, depending on it's embryonic location will generate either the spinal cord or brain.