noun
or neuron theory
: a theory in anatomy and physiology: the nervous system is composed of nerve cells each of which is a structural unit in contact with other units but not in continuity, a genetic unit derived from a single embryonic neuroblast, a functional unit or unit of conduction with the nervous pathways being chains of such units, and a trophic unit with the nerve processes degenerating when severed from the cell body and being replaced by outgrowths from the cell body