The motor functions we have described so far in this part of the book have been concerned with the control of skeletal muscles. These are the muscles that produce overt movements of the body and give rise to the observable external actions that we normally think of as the “behavior” of an animal. However, even in an animal that appears to an external observer to be quiescent, the nervous system is quite busy coordinating many ongoing motor actions that are as important for survival as skeletal muscle movements. These motor activities include such things as regulating digestion, maintaining the proper glucose balance in the blood, regulating heart rate, and so on. The part of the nervous system that controls these functions is called the autonomic nervous system. The motor targets of the autonomic nervous system include gland cells, cardiac muscle cells, and smooth muscle cells such as those found in the gut. To distinguish it from the autonomic nervous system, the parts of the nervous system we have been discussing up to this point whose motor targets are the skeletal muscles are collectively called the somatic nervous system.