Ventral nerve cord
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The ventral nerve cord (VNC) makes up a part of the central nervous system of some phyla of the bilaterians, particularly within the nematodes, annelids and the arthropods. It usually consists of the segmental ganglia anteriorly with the nerve cords running down the ventral ("belly", as opposed to back) plane of the organism.
Ventral nerve cords from anterior to posterior (the thoracic and abdominal tagma in the arthropods) are made up of segmental ganglia that are connected by a tract of nerve fibers passing from one side to the other of the nerve cord called commissures . The complete system bears some likeness to a rope ladder. In some animals the bilateral ganglia are fused into a single large ganglion per segment.
VNCs have been described in over 300 insect species covering all the major insect orders. The presumed common ancestral structure is rarely observed; instead the VNCs of most insects show extensive modification as well as convergence. Modifications include shifts in neuromere positions, their fusion to form composite ganglia, and, potentially, their separation to revert to individual ganglia.
"engrailed" is a transcription factor that helps regulate the gene "frazzled" in order to separate neuroblast during embryonic development. The segregation of neuroblast is essential for the formation and development of the ventral nerve cord.
- Niven, Jeremy E.; Graham, Christopher M.; Burrows, Malcolm (2008). "Diversity and Evolution of the Insect Ventral Nerve Cord". Annual Review of Entomology. 53 (1): 253–271. doi:10.1146/annurev.ento.52.110405.091322. ISSN 0066-4170. PMID 17803455.
- Joly, Willy; Mugat, Bruno; Maschat, Florence (2007). "Engrailed controls the organization of the ventral nerve cord through frazzled regulation". Developmental Biology. 301 (2): 542–554. doi:10.1016/j.ydbio.2006.10.019. PMID 17126316.