A group of nerve cell bodies outside the central nervous system of the body is called as ganglion. The nerve is an enclosed cable like bundles of axons. A neuron is a nerve cell (electrically excitable) that receive, process and transmit signalling information through electrical and chemical signals. The tracts are the bundle of fibers that connects nuclei of the central nervous system. The nerves, neuron and tracts are present outside the central nervous system. Hence, only ganglia persists in the central nervous system.
