Notochord
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222108806
2008-06-27T16:28:49Z
81.171.175.130
Removed out-dated and misleading reference
{{Infobox Embryology |
Name = {{PAGENAME}} |
Latin = |
GraySubject = 8 |
GrayPage = 52 |
Image = Image19.png |
Caption = Transverse section of a chick embryo of forty-five hours’ incubation. |
Image2 = |
Caption2 = |
System = |
CarnegieStage = |
Days = |
Precursor = [[chordamesoderm]] |
GivesRiseTo = [[nucleus pulposus]] |
MeshName = Notochord |
MeshNumber = A16.254.610 |
DorlandsPre = n_10 |
DorlandsSuf = 12579301 |
}}
The '''notochord''' is a flexible, rod-shaped body found in [[embryo]]s of all [[chordate]]s. It is composed of [[cell (biology)|cell]]s derived from the [[mesoderm]] and defines the primitive axis of the [[embryo]]. In lower [[vertebrate]]s, it persists throughout life as the main [[axial skeleton|axial support]] of the body, while in higher vertebrates it is replaced by the [[vertebral column]]. The notochord is found on the [[anatomical terms of location|ventral]] surface of the [[neural tube]].
Notochords were the first "backbones", as well, serving as support structures in chordates that lacked a bony skeleton. The very first vertebrates, such as ''[[Haikouicthys]]'', had only a notochord. Embryos of vertebrates have notochords today, as embryonic development often happens to follow a pattern similar to the ancestral evolution of the modern animal's traits. Notochords were advantageous to primitive fish-ancestors because they were a rigid structure for muscle attachment, yet flexible enough to allow more movement than, for example, the exoskeleton of the dominant animals of that time. In humans, they eventually develop into the [[nucleus pulposus]] of the [[intervertebral discs]].
In the adult human, a notochord remnant is the [[apical ligament]] of the [[atlanto-axial joint]].
==Development of the notochord==
'''Notogenesis''' is the development of the notochord by the [[epiblast]]s that make up the floor of the [[amnion]] cavity ([http://www.embryology.ch/anglais/hdisqueembry/triderm03.html Human Embryology]). The notochord arises as a pouch from the mesoderm.
==The notochord in neural development==
Research into the notochord has played a key role in understanding the development of the [[central nervous system]]. By transplanting and expressing a second notochord near the [[anatomical terms of location|dorsal]] neural tube, 180 [[degree (angle)|degree]]s opposite of the normal notochord location, one can induce the formation of [[motoneuron]]s in the dorsal tube. Motoneuron formation generally occurs in the ventral neural tube, while the dorsal tube generally forms sensory [[cell (biology)|cells]].
The notochord secretes a protein called [[sonic hedgehog|sonic hedgehog homolog]] (SHH), a key [[morphogen]] regulating [[organogenesis]] and having a critical role in signaling the development of motoneurons<ref>Echelard Y, Epstein DJ, St-Jacques B, Shen L, Mohler J, McMahon JA, McMahon AP. Sonic hedgehog, a member of a family of putative signaling molecules, is implicated in the regulation of CNS polarity. ''Cell'' 1993;75(7):1417-30. PMID 7916661</ref>. The secretion of SHH by the notochord establishes the ventral pole of the dorsal-ventral axis in the developing embryo.
==Additional images==
<gallery>
Image:Gray14.png|Surface view of embryo of Concolor gibbon (''[[Hylobates concolor]]'').
Image:Gray29.png|Diagram of a transverse section, showing the mode of formation of the amnion in the chick.
Image:Gray898.png|Section through the head of a human embryo, about twelve days old, in the region of the hind-brain.
Image:Gray1111.png|Transverse section of human embryo eight and a half to nine weeks old.
</gallery>
{{Development of nervous system}}
==References==
<references />
[[Category:Developmental neuroscience]]
[[Category:Embryology]]
[[ca:Notocordi]]
[[cs:Struna hřbetní]]
[[de:Chorda dorsalis]]
[[es:Notocorda]]
[[eo:Notokordo]]
[[fr:Notochorde]]
[[it:Notocorda]]
[[lt:Chorda]]
[[ja:脊索]]
[[pl:Struna grzbietowa]]
[[pt:Corda dorsal]]
[[ru:Хорда (зоология)]]
[[ta:முதுகுநாண்]]
[[vi:Dây sống]]
[[tr:Notokorda]]