Also, extending from the free surface of the cell are numerous microvilli containing actin microfilaments (Fig. 1-17). The cytoplasm stains intensely, having an electron density about equal to that of the oligodendrocyte, whereas the nucleus has a similar density to that of the astrocyte. Microtubules; large whorls of filaments; coated vesicles; rough ER; Golgi apparatus; lysosomes; and abundant small, dense mitochondria are also present. The base of the cell is composed of involuted processes that interdigitate with the underlying neuropil. The lateral margins of each cell characteristically display long, compound, junctional complexes (Fig. 1-18) made up of desmosomes, termed zonula adherentes, and gap junctions [3]. Overlying specialized secretory zones around the ventricles, the so-called subventricle organs and choroid plexus, the ependymal lining is different and the cells are connected at their apical poles by tight junctions called zonula occludentes. Desmosomes and gap junctions are also present at the lateral aspects of the cells [39].