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/näCH/ Noun, pl. notches (Anatomy) 1. V-shaped cut, indentation, or nick, especially at the edge of an object or structure. ( (Developmental biology) 1. A family of receptors, which upon binding with ligands, plays a major role in neurogenesis, specifically during lateral inhibition (wherein neuroblasts are singled-out from the neuroectoderm) and during binary cell fate specification (wherein ectodermal cells are prevented from differentiating into neuroblasts). ( (Other definitions) 1. A deep close pass; a gap. ( 2. A rounded indentation cut into the pages of a book on the edge opposite the spine. ( 3. The location in a range of mountains of a geological formation that is lower than the surrounding peaks. ( Word origin: From Middle French oche “notch,” from Old French ochier “to notch,” of unknown origin. Said to be unconnected to nock. Verb 1. Cut or make a notch into. ( 2. Notch a surface to record something....

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/ˈnōtəˌkôrd/ Noun, pl. notochords 1. A flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc. The notochord is found ventral to the neural tube. ( 2. A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine. ( 3. A similar structure found in the embryos of vertebrates from which the spine develops. ( 4. A longitudinal flexible rod of cells that in the lowest chordates (as a lancelet or a lamprey) and in the embryos of the higher vertebrates forms the supporting axis of the body. ( Word origin: coined in English by English anatomist Sir Richard Owen (1804-1892) from chord, alteration of cord (n.), by influence of Greek khorde “gut-string, string of a lyre, tripe,” + comb. form of Greek noton...

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