[Aging of nerve tissue].

In the peripheral nervous system, the various alterations, which are the manifestations of the ageing deleterious process, appear according to a precise chronology and, obviously, degradation does not depend on the cell body microenvironment. On the other hand, alterations in the fibres environment could enhance the deleterious process. Similarly, the quality of the environment of the organism itself could act to modulate the spreading of the alterations. It should be strenghtened that the neuron never losses its capacities to react against aggressions, for instance by forming new fibres. In the central nervous system, a toxic activity develops with advancing age, which could be responsible for the neuronal depopulation. Schematically, the neuronal capacities during ageing appear more dependent on the relationships between the neurons and their target organs than on the neurons themselves.