ABSTRACT
Two types of stimuli that continuously bombard a complex organism such as a mammal are neural and antigenic, either of which may arise externally or internally. Neural stimuli act via the "senses" communicating with the exterior environment, or may arise as emotions, abstract thought, or visceral sensations via the cerebral cortex, limbic system, hypothalamus, and the autonomic nervous system. Antigenic signals act via any of the external orifices or breaks in the integument or from various changes within the organism. Either type of stimulus sets off a chain of reactions involving the nervous, immune, and endocrine systems (1-6).
