Bundles of nerve processes within the central nervous system are called fasciculi, tracts or funiculi, depending upon their size. All of these are types of neural pathways, cords of white neural matter that connect different parts of the nervous system.
The smallest unit of any neural pathway is the individual nerve cell, or neuron. Neurons have long tendrils called axons, which are used to communicate signals from one cell to the next. Fasciculi are bundles of axons. Funiculi are bundles of fasciculi. Funiculi are not continuous strands and frequently fuse and divide along their length. Within the spinal cord, fasciculi and funiculi are specialized for carrying certain kinds of information to and from the brain.