The central nervous system is so-called because it affects everything in your body. Moreover, the evolution of biology results in something familiar to computer programmers, something which looks a lot like “growth by bug fix”. The result is a highly interdependent system, the components of which cannot be easily teased apart from the others without breaking something, many times fatally. That aside, the nervous system is traditionally divided up between the central nervous system (brain and spinal column) and the periphery nervous system (gut and the extended nervous system). There is some debate whether the gut should be declared a third major component of the nervous system, independent of but highly integrated with the brain through such conduits as the vagus nerve bundles.
