Nervous system. Composite computer artwork of the human nervous system. The figure at right shows the principal nerve pathways of the body. The brain and the spinal cord 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 PNS collects information from the body and relays it to the CNS for processing. The CNS then sends appropriate response signals to the PNS. Nerve impulses are passed between neurons across synapses (top). Across centre and bottom are muscle fibres. The contraction and relaxation of muscle fibres is controlled by the nervous system.