There are two sections to the nervous system. The central nervous system (CNS) comes first, followed by the peripheral nervous system (PNS). The brain and spinal cord make up the central nervous system. The nervous system is also derived from ectoderm. The peripheral nervous system also connects nerves that connect muscles and sensory organs to the central nervous system. During swimming, the nervous system is responsible for control and coordination. There are ten cranial nerves in some fish, such as Scoliodon.