The long-standing model of pigment cell origins is implicitly based upon a progressive fate restriction model of neural crest development and postulates the existence of a partially restricted progenitor common to all pigment cell types (i.e., a chromatoblast) [38] .
Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals. It is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride.
sodium. a chemical element, atomic number 11, atomic weight 22.990, symbol Na. (See Appendix 6.) Sodium is the major cation of the extracellular fluid, constituting 90 to 95 per cent of all cations in the blood plasma and interstitial fluid; it thus determines the osmolality of the extracellular fluid.ts atomic number is 11, and its atomic weight is 22.9898. Sodium is one of the most important elements in the body. Sodium ions are involved in acid-base balance, water balance, the transmission of nerve impulses, and the contraction of muscle.