<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> <P> Spinal nerve C1 is called the suboccipital nerve, which provides motor innervation to muscles at the base of the skull . C2 and C3 form many of the nerves of the neck, providing both sensory and motor control . These include the greater occipital nerve, which provides sensation to the back of the head, the lesser occipital nerve, which provides sensation to the area behind the ears, the greater auricular nerve and the lesser auricular nerve . </P> <P> The phrenic nerve is a nerve essential for our survival which arises from nerve roots C3, C4 and C5 . It supplies the thoracic diaphragm, enabling breathing . If the spinal cord is transected above C3, then spontaneous breathing is not possible . </P>

Which structure is not a part of the peripheral nervous system (pns)