A brief look at glial cells.

Glial cells are numerically the dominant cell type in the central and peripheral nervous system. They are intermixed with the nerve cells and are found in intimate contacts with neuronal cell bodies, dendrites, axons and synaptic contacts. Like neurons, glial cells are a heterogeneous population of cells that differ in developmental origin, molecular composition, structure and activity. When these cells were first discovered some 150 years ago they were viewed as a type of connective tissue support for nerve cells. They are now known to be essential for the development and function of the brain and other parts of the nervous system. They are also central players in a large number of pathological processes. We have therefore moved away from a view of the nervous system as a system of neurons, to the appreciation that it is a neural system where the contributions of both nerve and glial cells are intimately integrated, interdependent and obligatory.