At about the third week of prenatal development, the ectoderm of the embryonic disk forms the neural plate, which folds at the edges into the neural tube.
It begins to differentiate under the influence of the nearby notochord and paraxial mesoderm.
A group of cells migrates to form the neural crest, which gives rise to dorsal and autonomic ganglia, the adrenal medulla, and other structures.
The middle portion of the neural tube closes first; the openings at each end close later.