Nervous system. Computer artwork of the principle nerve pathways of the human body. The brain (top centre) and the spinal cord (down centre) comprise the central nervous system (CNS). Spinal nerves extend from the spinal cord to every part of the body, forming the peripheral nervous system (PNS). The main nerves of the arms are the median and ulnar nerves, and the main nerves of the legs are the femoral nerves. The PNS collects information from the body and relays it back to the CNS for processing, which sends out appropriate response signals to the PNS.