The cranial part, which gives rise to the adult brain, becomes dilated and constitutes the primitive brain, or archencephalon the caudal part, which gives rise to the adult medulla, remains with a uniform caliber and constitutes the primitive medulla of the embryo. The neural tube gives rise to elements of the central nervous system, while the crest gives rise to elements of the peripheral nervous system, in addition to elements not belonging to the nervous system.ДЇrom the beginning of its formation, the diameter of the neural tube is not uniform. At the point where this ectoderm meets the lips of the neural groove, cells develop that form on each side a longitudinal lamina called the neural crest. The undifferentiated ectoderm then closes over the neural tube, thus isolating it from the external environment. The lips of the neural gutter fuse to form the neural tube. The neural plate grows progressively, becomes thicker, and acquires a longitudinal groove called the neural groove that deepens to form the neural groove. Notochord or mesoderm extirpations in young embryos resulted in large marrow anomalies. Notochords implanted in the abdominal wall of amphibian embryos induce neural tube formation there. It is known that the formation of this plate and the subsequent formation of the neural tube plays an important role in the inducing action of the notochord and mesoderm. The first index The process of formation of the nervous system consists of a thickening of the ectoderm, situated above the notochord, forming the so-called neural plate. Of the three embryonic layers, the ectoderm is the one that is in contact with the external environment of the organism and it is from this layer that the nervous system originates. cf, cephalic flexure d, diencephalon or, optic recess os, optic stalks po, preoptic area pt, posterior tuberculum t, telencephalon.During the evolution of the living being, we saw that the first neurons appeared on the external surface of the organism, considering that the primary function of the nervous system is to relate the animal to the environment. Nodal-dependent otp1 expression in PT is required for the proper differentiation of a subset of CA neurons. In PT, otp1 expression is independent from HH and FGF signaling cascades, but it is activated by Nodal in a HH-independent way. otp1 expression in PO is modulated negatively by FGF8 and positively by SHH the effect of SHH on otp1 expression is diminished by Dzip1, a negative regulator of SHH signaling, and Nodal activates otp1 expression through SHH. B, presumptive Nodal, HH, and FGF signaling cascades genetic interactions regulating otp1 expression in the two hypothalamic areas indicated by solid arrows. otp1, fgf8 and shh expression domains are painted with different colors (purple, otp1 blue, shh red, fgf8). A, schematic lateral view of the zebrafish forebrain with anterior to the left and dorsal up. Schematic representation of the spatial and functional links between otp1 expression and Nodal, SHH and FGF signaling cascades in the 24 hpf hypothalamic forebrain.

Cephalic flexture