Ultrastructure of the nervous system

Within the nervous system, five cell types were studied by the electron microscope: the neuron, astrocyte, oligodendroglia, microglia and ependymal cells. The neurons are characterized by the Nissl substance within the perikaryon, the neurotubules and the neurofilaments. The three types of glial cells can be distinguished from one another. The astrocyte has relatively lucent cytoplasm and contains filaments which extend into long cytoplasmic processes. The oligodendroglia has electron-dense cytoplasm with thin extensions wedged between the cellular processes of the neuropil. The microglia cytoplasm is similar to the oligodendroglia but can be differentiated by the peculiar convoluted outline of the nuclear membrane and the clear space which separate the nucleus from the cytoplasm. The ependymal cell has characteristic microvilli and cilia at its ventricular surface. The cytoplasm contain parabasal bodies and tight junctions between adjacent cells. In the peripheral nerve, the axon and the myelin sheath are located within the Schwann cells. The terminal nerve endings from enlargements filled with synaptic vesicles. Electron microscopy of the nervous system is not only essential for research, but is also helpful in diagnosis of certain diseases.