Every living organism must be able to react appropriately to changes in its environment if it is to survive; by surviving, it increases the chance of survival of the species.
The regulation of these reactions is the responsibility of the nervous system, incomparably the most complicated of the body systems.
A purely descriptive account, of the brain in particular, has a very limited value or appeal; an account that attempts an adequate explanation of function encounters certain problems.
Many of the structures and pathways of which the central nervous system is composed are neither discrete nor identifiable by the usual methods of anatomy; the majority of the “functional units” that it is convenient to recognize have multifarious and complex connections with other such units. There are parts to which it is impossible to pin specific functional labels, either because their significance is unknown or because of a multiplicity of associations.The compromise adopted in this chapter is the presentation of an initial formal description followed by short and rather elementary digressions on the functional significance of a few selected units. These digressions have as their prime purpose the attachment of some “meaning” to the structures previously described. We do so knowing that more complete functional analyses will be provided by concurrent or later courses of physiology or neurology.