3 concepts
Clusters of Neuronal Cell Bodies
A nucleus can either by a relatively compact collection of neurons or a distinctly identifiable group of neurons spread over a large area.
Axon Bundles
A bundle of axons is called a nerve in the peripheral nervous system and a tract in the central nervous system.
Grey and White Matter
The basic pattern of the CNS is a central cavity surrounded by gray matter made up of neuronal cell bodies external to which is the white matter which is made up of myelinated axons.