Neural induction

The central nervous system originates from the midline region as a specialized area of ectoderm, the neuroectoderm or neural plate. As the neuroectodermal cells proliferate an indentation, the neural groove, forms in the neural plate. The lateral folds of this groove join in the midline, forming the neural tube. The folds begin to fuse in the central part of the groove but the most rostral and caudal parts do not close, leaving rostral and caudal neuropores. A small transitional zone between the neural plate and the surrounding ectoderm provides the cells of the neural crest, which differentiate into the sensory cells of the spinal cord, the cranial ganglionic cells of the somatic and autonomic nervous systems, Schwann cells, and chromaffine cells.

Neural tube formation requires a controlled expression of cell adhesion molecules in the lateral folds of the neural groove. If the rostral neuropore fails to close, the development of the forebrain is impaired leading to anencephalus. If the caudal neuropore fails to close, the most severe result is rachischisis, a malformation with a dorsally exposed neural groove which has severe neurological consequences. The mildest result is spina bifida occulta which is a cleft of a vertebral arch covered by epidermis.

As development continues, the neural tube and crest move to a position between the ectoderm and the notochord. The rostral part of the neural tube differentiates into the brain; the caudal part differentiates into the spinal cord behind the fifth somite.

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