<P> The somatic system includes the sensory nervous system and the somatosensory system and consists of sensory nerves and somatic nerves, and many nerves which hold both functions . </P> <P> In the head and neck, cranial nerve s carry somatosensory data . There are twelve cranial nerves, ten of which originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions . The nuclei of the olfactory nerve and the optic nerve s lie in the forebrain and thalamus, respectively, and are thus not considered to be true cranial nerves . One unique cranial nerve is the vagus nerve, which receives sensory information from organs in the thorax and abdomen . The accessory nerve is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which being exclusively in the head . </P> <P> For the rest of the body, spinal nerves are responsible for somatosensory information . These arise from the spinal cord . Usually these arise as a web ("plexus") of interconnected nerves roots that arrange to form single nerves . These nerves control the functions of the rest of the body . In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal . These nerve roots are named according to the spinal vertebrata which they are adjacent to . In the cervical region, the spinal nerve roots come out above the corresponding vertebrae (i.e., nerve root between the skull and 1st cervical vertebrae is called spinal nerve C1). From the thoracic region to the coccygeal region, the spinal nerve roots come out below the corresponding vertebrae . It is important to note that this method creates a problem when naming the spinal nerve root between C7 and T1 (so it is called spinal nerve root C8). In the lumbar and sacral region, the spinal nerve roots travel within the dural sac and they travel below the level of L2 as the cauda equina . </P> <P> The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that serve the neck and back of head . </P>

The peripheral nervous system transmits information to and from the central nervous system