neurulation (redirected from Neural tube defect, folate-sensitive)

neurulation [‚nu̇r·ə′lā·shən]

(embryology)

Differentiation of nerve tissue and formation of the neural tube.

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Neurulation

The process by which the vertebrate neural tube is formed. The primordium of the central nervous system is the neural plate, which arises at the close of gastrulation by inductive action of the chorda-mesoderm on the overlying ectoderm. The axial mesodermal substratum causes the neural ectoderm to thicken into a distinct plate across the dorsal midline and influences both its size and shape. Its shieldlike appearance, broader anteriorly and narrower posteriorly, presages the areas of brain and spinal cord, respectively. The lateral edges of the neural plate then rise as neural folds which meet first at the level of the future midbrain, above the dorsal midline, then fuse anteriorly and posteriorly to form the neural tube. The body ectoderm becomes confluent above the closing neural tube and separates from it. Upon closure, the cells (known as neural crest cells) which occupied the crest of the neural folds leave the roof of the tube and migrate through the mesenchyme to all parts of the embryo, forming diverse structures. The neural tube thus formed gives rise to the brain and about half of the spinal cord. The remainder of the neural tube is added by the tail bud, which proliferates a solid nerve cord that secondarily hollows into a tube. See Nervous system (vertebrate), Neural crest