Neuroglial cells constitute a separate class of cells in the nervous system; they have been studied intensively since their original description by Virchow in 1846. As a rule anatomists find no difficulty in recognizing them by their staining properties, their shape and configuration as well as by their characteristic location between and around neurons. Electron microscopy has in recent years added much important subcellular detail and has shown how intermingled neurons and glial cells are, being separated from each other by narrow clefts 100 to 200 Å wide (figures 1
A, B
and 5, plates 1, 2 and 4). These studies have not changed the well-established grouping of mammalian glial cells into two main classes, the
oligodendrocytes
and the
astrocytes
. It is customary to state that glial cells outnumber neurons by 10 to 1 in the vertebrate nervous sytem. They are, however, smaller and according to some rough estimates they make up as much as 50% of the volume of mammalian brains. That glial cells differ significantly from neurons was clear from the beginning because they do not possess axons and, unlike mammalian neurons, they retain their ability to divide throughout life. The possible role of the large mass of glial cells in our nervous system has been of continued interest. During the past decade this interest in the physiology of neuroglia has been reinforced, largely under the stimulus of electron-microscopic and chemical studies of the nervous system. Among the numerous recent reviews and symposia only a few will be mentioned (Windle 1958; Nakai 1963; Mugnaini & Walberg 1964). The recent studies of the physiology of neuroglial cells have been reviewed by Kufller & Nicholls (1966) and a bibliography on neuroglia has been compiled by Little & Morris (1965).
On the Role of Glial Cells in the Mammalian Nervous System
