The somatic nervous system controls voluntary, conscious motor functions (skeletal movement and sensory movement), whereas the autonomic nervous system controls involuntary functions (such as smooth muscles, cardiac muscles and glandular movement). Furthermore, the systems differ in where they connect in the body.
The nervous system is composed of all the nerve tissue in the body. This system is further divided into other nervous systems, grouped together by type of nerve tissue. Two of these systems are the somatic and autonomic nervous systems. Biologically, the somatic nervous system connects external sensory organs through the brain to the muscles; the autonomic nervous system, on the other hand, connects the brain, spinal cord, organs, and glands. These connections in the body cause the systems to have their different functions in the nervous system.
Because the somatic system connects with muscles and external organs (ears, eyes, skin, nose and some areas of the mouth), it assists in people perceiving feelings associated with the senses, as well as sensations like pain and pleasure. However, these last two feelings are processed by other parts of the nervous system. The autonomic system connects internal areas of the body, so it perceives things like digestion, glandular movements and heartbeats. Although essential to the entire system, the autonomic and somatic systems are only two pieces in the massive human nervous system.