The body is made up of many millions of cells that grouped together form tissues, which form organs whose functions overlap to produce the body"s systems. In this chapter we consider the major systems of the body, examining how each system functions normally and looking at some of the disorders to which the system may be vulnerable. The body"s systems are, however, interconnected, and as was the case with rick, disruptions in one system can result in problems in other systems. The nervous system is a complex network of interconnected nerve fibres that functions to regulate many important bodily functions, including the response to and recovery from stress. The nervous system is made up of the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and the spinal cord. The rest of the nerves in the body, including those that connect to the brain and spinal cord, constitute the peripheral nervous system.