The peripheral nervous system has several subdivisions. The first level consists of the somatic nervous system and the autonomic nervous system, which refer to the nerves just under the skin and the nerves everywhere else, respectively. Despite their names, both mostly execute automatically, but the autonomic nervous system is so named because it is responsible for the body’s maintenance functions, which have a reputation for being opaque to conscious control. The nerves we use to consciously control our bodies are part of the somatic nervous system, but these function automatically even in the event of a coma.
The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems. A third division, the enteric nervous system, is also occasionally referred to. The sympathetic nervous system responds to stress, danger, and the like, and is responsible for the release of adrenaline, among other things. The parasympathetic nervous system is dominant during rest and helps us go to sleep and digest food. These two nervous systems tend to balance each other, creating a degree of harmony in the body. The enteric nervous system is responsible for some nerves around the intestines, and is known to function properly even when disconnected from the other two systems.