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Neurulation is the development of the nervous system in the vertebrates, at the thickened area above the notochord in ectoderms. The neural plate will fold to produce the neural tube which will develop into the brain. Remaining tissue will develop into the spinal cord. Neurula involves the formation of an internal neural tube from an external sheet of cells. The first signs of neurulation are flattening and thickening of the ectoderm overlying the notochord; this thickened area forms a neural plate. The edges of the neural plate that run in an anterior-posterior direction continue to thicken, forming ridges or folds. Between these neural folds, a groove forms and deepens as the folds roll over it to converge on the midline. The fold fuses, forming a cylinder--the neural tube--and a continuous overlying layer of epidermal ectoderm. The neural tube develops bulges at the anterior end, which become the major divisions of the brain. The remaining sections of the tube becomes the spinal cord.
In humans, failure of the neural tube to develop normally can result in serious birth defects. If the neural folds fail to fuse in a posterior region, the result is a condition known as spina bifida. If they fail to fuse at the anterior end, an infant can develop without a forebrain - a condition called anencephaly.
There are genetic as well as dietary factors that cause neural tube defects. The incidence of neural tube defects used to be about 1 in 300 live births, but we now know that this incidence can be cut in half if pregnant women have an adequate amount of folic acid in their diets.
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