The central nervous system in scanning electron microscopy.

The first decade of scanning electron microscopy of the central nervous system has emphasized study of the ventricular system, especially the circumventricular organs. These are largely non-ciliated areas located in close vicinity to the third and fourth ventricles. Supraependymal cells (neurons and phagocytes) are common here along with tanycytes. Occasionally small blood vessels are exposed. Neurosecretory function is established for some of these organs and suspected for most of them. The subarachnoid space is clearly lined by flat surfaced connective tissues with fenestrations. Free cells which are known to be macrophages are common on the natural surfaces. These tissues react to antigens in the manner of connective tissues elsewhere in the body. The "non-surface" areas of the central nervous system have been examined by various techniques utilizing fracturing, isolation and ultrasonication but an established methodology has not yet emerged.