Every living organism must be able to react appropriately to changes in its environment if it is to survive.

The detection of these environmental changes, their subsequent integration and interpretation, and finally, the production of a behavioral response are the function of the nervous system, incomparably the most complicated of the body systems.

The immense complexity of the nervous system occurs at the microscopic level and, as such, cannot be appreciated by a review of its gross structure. Ongoing advances in research methods, including the development of genetic, molecular, and optical tools, has allowed us to examine and manipulate the activity of individual cells and circuitry, but sufficient detailed knowledge of the complex and diverse connections making up the neural circuits of the nervous system still eludes us. Nevertheless, there is much to be learned from a description of the organization of the nervous system and the general functional regions, of the brain in particular, keeping in mind that there is much we still do not understand.

The approach in this chapter is the presentation of an initial description of the basic organization, cells, and circuitry of the nervous system followed by a more detailed region-by-region description of neural development, morphology, and function. We use it knowing that more complete functional analyses will be provided by concurrent or later courses of physiology and neurology.