The central nervous system or CNS consists of the cerebellum, cerebrum, brain stem, and spinal cord.
The neuron is the basic working unit of the nervous system.
And the neuroglia or glial cells are the non-neuronal cells that support and protect the nervous system.
The central neuroglia includes astrocytes, oligodendrocytes, ependymal cells, and microglia.
The peripheral neuroglia includes Schwann cells, satellite cells, and a number of cells associated with specific organs.
Macroscopically the CNS is made of white matter and grey matter.
The difference in appearance is from the lipid-rich myelin sheaths that cover the axons present in white matter.
Whereas the grey matter consists mostly of neuron cell bodies, dendrites, astrocytes, and microglial cells.
In this high power image of white matter from the spinal cord, the axons are surrounded by clear white space, which is where the myelin was present before the tissue was processed to create this slide.
The outermost portion of the cerebrum and cerebellum consist of grey matter, with their white matter present mainly in the deeper regions of the brain.
One the other hand, the spinal cord has the opposite arrangement, with white matter mainly in the periphery and grey matter mostly located closer to the center, forming an “H” or butterfly-shaped appearance when looking at a cross-section of the spinal cord.