The peripheral nervous system consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some of those nerve pairs are exclusively sensory cells, such as those involved in smell and vision. Others are exclusively motor cells, such as those involved with eyeballs and hearing. Also, there are nerve pairs that have both sensory and motor cells, such as those involved in taste and some aspects of swallowing.

Sensory cells carry messages to the central nervous system. Motor cells carry the signal from the central nervous system to the internal organs, muscles, and glands in the periphery or the outer edges of the body. Both types of cells travel together to the spinal cord, but then they separate into two areas. One area is called the posterior sensory root and the other is called the anterior sensory root.

The motor nerve cells are either somatic or autonomic. The somatic nerve cells carry messages from the outer areas of the body having to do with the senses. It is like a passageway from the environment to the central nervous system. That seems simple compared to the autonomic cells because the autonomic nerve cells are divided into three separate divisions called the parasympathetic, the sympathetic, and the enteric divisions.

These divisions are named by the functions that they are involved in throughout the body. This will be discussed later in detail in the lesson, but as a sneak preview, here is a brief description for each division. The parasympathetic division is involved with slowing body functions; while the sympathetic division increases body