Nerves V and VII, respectively. The innervation pattern provides connectional evidence for homologies between the individual auditory ossicles and the jaw bones from which they were evolutionarily derived. Neuronal cell bodies, dendrites and axonal terminals, are synaptically connected in precise arrangements. In each region a subset of the neurons, typically relatively few in number, termed principal neurons, project axons to other areas, forming the entire output of the region. They may receive axonal inputs from principal neurons located in other regions, or from local circuit neurons from their own region, or from both sources.
Axons coursing between such areas travel in well organized bundles.
In gnathostomes long axons are usually wrapped in an insulating layer of myelin, which gives the fresh neural tissue a bright white appearance and is termed CNS white matter. The pictures of the human spinal cord show that gray matter is located deep within the cord, and white matter is superficial. The lamprey swim Local regions of the central nervous system can organize information, or produce information de novo from almost nothing. To show this, consider a fish, a lamprey, swimming. During swimming, muscles contract rhythmically.