nucleus /n(y)o̅o̅″klē·əs/ [L, nut kernel] , 1. the central controlling body within a living cell, usually a spheric unit enclosed in a membrane and containing genetic codes for maintaining life systems of the organism and for issuing commands for growth and reproduction. −nuclear, adj. 2. a group of nerve cells of the central nervous system having a common function, such as supporting the sense of hearing or smell. 3. the center of an atom consisting of an element-specific number of protons and neutrons. A probability cloud of electrons exists around the atomic nucleus. 4. adj., the central element in an organic chemical compound or class of compounds. Formerly called cytoblast.
