Central nervous system

Central nervous system consists of the brain and spinal cord. It is composed entirely of neurons, their axons and dendrites, and the supporting cells of the central nervous system. Macroscopically, central nervous sytem is made up of gray and white matter (substantia grisea et alba). The gray matter contains most of the neuron cell bodies, dendrites, the initial unmyelinated portions of axons, astrocytes, and microglial cells, whereas the main components of white matter are myelinated axons (lipids in the myelin sheaths account for the white appearance of the white matter) and the myelin producing oligodendrocytes. The white matter is devoid of neuronal cell bodies, but microglial cells are present. Aggregates of neuronal cell bodies in the white matter are called nuclei.

In the cortex of cerebrum and cerebellum the gray matter overlies the central medullary mass of white matter. In the spinal cord the situation is in opposite, the gray matter is located centrally (in cross sections has H-shape and somewhat resembles the “butterfly”) surrounded by the white matter.