The Nervous System
The nervous system is the master controller of the body. Each thought, each emotion, each action—all result from the activity of this system. Through its many parts, the nervous system monitors conditions both within and outside the body. It then processes that information and decides how the body should respond, if at all. Finally, if a response is needed, the system sends out electrical signals that spur the body into immediate action. Although one of the smallest of the body's systems in terms of weight, the nervous system is the most complex and versatile.