Changes in Nervous System with Age

specialized and diversified. The individual nerve cells in one small circumscribed area or nucleus may be markedly different in structure, action, and reaction from those neurons that form an adjacent group. These neurons, even with their many unsolved problems, are far better known anatomically and physiologically than the greater bulk of the nervous system, their supportive structures. These structures, including the glia and the ground substance, are within the bounds of the existing frontiers of neuroanatomy and neurophysiology. So much of the normal picture of the nervous system is so scantily known that departures from the normal are at best determined with difficulty. A host of neuroanatomical alterations in the nervous system accompanying the process of aging have been described. Many of these socalled manifestations of aging occur in the very young as well as in the old. Some of these, when they occur in the young are undoubtedly abnormal, whereas the frequency with which they occur in the old might cause them to be labeled as normal alterations accompanying aging. Aging should be looked upon primarily as a physiological stage and not a pathological condition. The normal alterations that bring about or occur with the gradual and continual advance from one plateau of life to another are apt to be quite subtle. They therefore are difficult to determine or locate accurately, and difficult to separate from abnormal changes brought about by modifications in internal or external environmental conditions as influenced by disease or trauma. The separation of these changes from artifacts or post-mortem changes, often uncontrollable in human material, cannot be overemphasized.