Neural crest

The cells of the neural crest originate in the zone of transition between the neuroectoderm (situated medially) and the surface ectoderm (situated laterally). By S9, i.e. before the closure of the neural tube, the neural crest cells leave the ectodermal layer in great numbers and migrate towards various parts of the body. The extracellular matrix serves as a guiding structure. In the brain (mainly in the optic vesicle, mesencephalon and rhombencephalon), the cells of the neural crest form by S13; in the spinal cord the formation of neural crest cells takes much longer. At this level, the neural crest first forms an unsegmented layer. However, cell migration becomes channelled and segmented by somites and the forming sclerotomes. Cells of the neural crest give rise to some of the head ganglia, the spinal and autonomous ganglia, amongst others. Note the chromaffin cells of the adrenal medulla and the ectomesenchyme, particularly in the area of the pharyngeal arches. Ectomesenchyme is mesenchyme which originates from cells of the neural crest.