Nucleus


 * 1) in cytology, typically a rounded or oval mass of protoplasm within the cytoplasm of a plant or animal cell, surrounded by a nuclear envelope, which encloses euchromatin, heterochromatin, and one or more nucleoli and undergoes mitosis during cell division Syn karyon
 * 2) by extension, because of similar function, the genome of microorganisms (microbes), which is relatively simple in structure, lacks a nuclear membrane and does not undergo mitosis during replication; more exactly termed nucleoid
 * 3) in neuroanatomy, a group of nerve cell bodies in the brain or spinal cord that can be demarcated from neighboring groups on the basis of either differences in cell type or the presence of a surrounding zone of nerve fibers or cell-poor neuropil
 * 4) any substance (e.g., foreign body, mucus, crystal) around which a urinary or other calculus is formed
 * 5) the central portion of an atom (composed of protons and neutrons), where most of the mass and all of the positive charge are concentrated
 * 6) a particle on which a crystal, droplet, or bubble forms
 * 7) a characteristic arrangement of atoms in a series of molecules; e.g., the benzene nucleus in a series of aromatic compounds