The nervous system is a set of nerve cells and other structures that ensure the work of all organs and systems of the body in constant interaction with the environment. The nervous system perceives external and internal stimuli, analyzes and processes information, regulates and coordinates the activities of the organism. In fish it is represented by the central and related peripheral and autonomic nervous system. The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes the nerves that depart from the brain and spinal cord to the organs. The autonomic nervous system is the numerous ganglia and nerves innervating the muscles of the internal organs and blood vessels of the heart.