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.
Transcript. DAVID POGUE (Technology Guru): Sodium: symbol Na; 11 protons and 11 electrons arranged in shells as two, eight and one. Sodium is an alkali metal. Like all the elements in this group, it's desperate to get rid of that extra electron.