The upper figure is a schematic drawing of the brain and cerebellum, organs that will be analyzed in the following pages.
The central nervous system has areas with a high concentrations of neuronal cell bodies and others with a high concentration of neuronal extensions, especially axons. These two regions can be well identified after a fresh recently removed brain or cerebellum is sectioned and observed macroscopically,
The regions with a high concentration of neuronal cell bodies show a grayish color and are thus called gray matter of the central nervous system. On the other hand, the regions with a large number of neuronal extensions have a great amount of myelinated nerve fibers and as a result of the high myelin concentation has a whitish color and is named white matter.
The gray matter is an important site of reception and integration of information and responses and the white matter contains a great number of pathways that connect different regions of the central nervous system.
The lower figure shows the distribution of white and gray matter in the brain.
The gray matter, that contains a high concentration of neuron cell bodies, is concentrated in two areas:
– at the the brain periphery, just below its surface, forming the cerebral cortex;
– in clusters of different sizes inside the brain, called brain nuclei.
The white matter occupies the interior of the brain, below the cortex and surrounding the nuclei.
The lower figure shows a cross-section of the brain and, in a simplified way, the distribution of its gray and white matter.
