The nervous and hormonal systems are critical in maintaining careful control of animal life.
The nervous system uses receptors to gather information about the function of the body and the world outside. It then provides fast response to that information, by acting on glands or muscles.
The hormonal system is made up of a number of glands throughout the body, which secrete hormones directly into the blood stream. These control a wide range of functions within the body. The action of the system is slower than the nervous system but has a more widespread and longer-lasting action.
The body is a complex interconnection of many different systems.
Each system operates within a careful balance.
If control is not kept, the systems don't work properly, we get sick and we would die. So it is important that we know how these systems work and what happens if it all goes wrong.