In insects the nervous system consists of a rudimentary brain and a nerve cord. This nerve cord, like that of most invertebrates, is double. It consists of a chain of ganglia, usually one in each body segment, which are connected to each other by two bundles of nerve fibers. The ganglia contain most of the nerve cell bodies. Each ganglion coordinates many of the responses in its own segment.
There is a major difference between an insect's nervous system and that of vertebrates. In insects and most other invertabrates the cell bodies of sensory neurons are not in central nervous system as they are in vertebrates. Instead the sensory verve cell bodies of insects and most other invertebrates are located out in the skin near the sensory receptors. Another major difference is the location of the whole nervous system. In insects the nerve cord lies underneath the gut, in a ventral position. In vertebrates the nerve cord lies in a dorsal position above the gut.