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Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.〔Larsen WJ. Human Embryology. Third ed. 2001.P 86.ISBN0-443-06583-7〕 The embryo at this stage is termed the neurula. The process begins when the notochord induces the formation of the central nervous system (CNS) by signaling the ectoderm germ layer above it to form the thick and flat neural plate. The neural plate folds in upon itself to form the neural tube, which will later differentiate into the spinal cord and the brain, eventually forming the central nervous system. Different portions of the neural tube form by two different processes, called primary and secondary neurulation, in different species. * In primary neurulation, the neural plate creases inward until the edges come in contact and fuse. * In secondary neurulation, the tube forms by hollowing out of the interior of a solid precursor. ==Primary neurulation== === Induction === Primary neurulation occurs in response to soluble growth factors secreted by the notochord. Ectodermal cells are induced to form neuroectoderm from a variety of signals. Ectoderm sends and receives signals of bone morphogenetic protein 4 (BMP4) and cells which receive BMP4 signal develop into epidermis. The inhibitory signals chordin, noggin and follistatin are needed to form neural plate. These inhibitory signals are created and emitted by the Spemann organiser. Cells which do not receive BMP4 signaling due to the effects of the inhibitory signals will develop into the anterior neuroectoderm cells of the neural plate. Cells which receive fibroblast growth factor (FGF) in addition to the inhibitory signals form posterior neural plate cells. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Neurulation」の詳細全文を読む スポンサード リンク
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