The Study of Neuroglia Under an Electron Microscope

With the help of a light microscope, you can see several types of cells: neuroglia lying next to neurons and their processes. Neuroglia of ectodermal origin consists of oligodendroglia, fibrous and protoplasmic astrocytes and cubic ependymal cells with cilia. The latter line the ventricles and the central canal of the brain and spinal cord. The smallest of the glial cells forming microglia are of mesodermal origin and can turn into phagocytes. Various types of glial cells are usually recognized using various staining methods. For example, on preparations stained by Nissl, it can be seen that astrocytes have the largest nuclei, usually oval in shape and most often with fine-grained, evenly distributed chromatin. Oligodendroglia cells have smaller rounded nuclei with dense lumps of chromatin, especially crowded at the nuclear envelope. The nuclei of microglial cells are smaller and more often elongated. Special methods of silvering reveal bundles of glial fibrils in the long undulating processes of fibrous astrocytes; in microglial cells, the cytoplasm is usually stained entirely; their several processes are characterized by branching at an "angle". In oligodendroglia cells, the nuclei are rounded: these are cells with a small number of short processes (as indicated by their name) or without any processes at all. Astrocytes, which are best seen when colored by Golgi, have numerous branching, feathery processes. These are the main features, but there are many differences, and since it is often impossible to reliably recognize all types of cells using light microscopy on a single slice of brain tissue, it is not surprising that even with electron microscopic examination, cells that are difficult to classify are often found. Nevertheless, a number of criteria have been established that can be used, however, with caution.