In vertebrate embryos, the formation of the neural tube via the neural plate from the ectoderm by a process of invagination and closure, including the caudal and rostral ends. When this happens, the embryo is referred to as the neurula. Somites, which cells that give rise to muscles, ribs, skin and vertebrae, are formed in pairs along the neural tube. Neurulation involves two processes, termed ‘primary’ and ‘secondary’/ In primary neurulation, the neural plate folds inwards so that the edges make contact and fuse. In secondary neurulation, the neural tube is formed from mesenchyme by hollowing out (or cavitation) a solid cord of cells. In mice, and probably humans, secondary neurulation begins at about the level of somite 35. The molecular signals for primary neurulation in humans are not fully understood, but is thought to involve the transcription factor sonic hedgehog made in the notochord and floor plate. As for secondary neurulation, Bone Morphogenic Proteins in the rostral end of the neural tube has been suggested as candidate.
See Bone morphogenic proteins (BMPs), Caudal, Ectoderm, Embryogenesis, Gastrulation, Holoprosencephaly, Mesenchyme, Neural crest, Neural plate, Neural tube, Neurula, Notochord, Polarizer, Rostral, Somites