Although semantics cannot be reduced to neurophysiology, it must have however a certain neurophysiologic basis and this paper deals with, that neurophysiologic basis which, in fact, has a neurocybernetic basis. The paper first approaches the relations between information and signification and their part within the nervous system's work. Then, it analyses semantic function discoverying neurocybernetic mechanisms which can be proper not only to the conventional signs but also to the objects and phenomena which in turn can play the sign's part. Finally, semantic levels of the nervous system, beginning with the most elementary level of unity, as letters are, and up to the level of the highest ideas and concepts the brain is working with, are described.