Chapter 8 - Nervous System

Abstract

The nervous system of fishes can be divided into central and peripheral parts. The central nervous system comprises the brain, spinal cord and two of the cranial nerves, while the peripheral nervous system comprises the rest of the cranial nerves and the spinal nerves. The central and peripheral nervous systems also can be divided into somatic and autonomic parts.The somatic nervous system supplies the various sensory receptor systems and the somatic muscles of the body wall and head, while the autonomic nervous system (which has sympathetic and parasympathetic divisions) supplies sensory and motor innervation to viscera and glands. Somatic motor innervation is via sets of single neurons with cell bodies in the central nervous system and axons that run in a cranial or spinal nerve to the muscle. Autonomic motor innervation is via a two-neuron chain with the first cell body in the central nervous system and the second within a peripherally located ganglion. Brain structure varies dramatically across fishes both between and within major groups. Part of this variation derives from fundamental differences in the embryological development of the brain between ray-finned fishes (actinopterygians) and other fishes.