ABSTRACT
The neurons carry out the specialized functions of the nervous system. The main supporting elements of the nervous system are the neuroglia or glia, the vasculature, and the connective tissues surrounding the various parts of the nervous system. Schwann celis may be regarded as neuroglial cells extending from the central nervous system as peripheral axons grew. Schwann cells are necessary to the life and function of the axons of the peripheral nervous system. The central nervous system contains blood vessels and is enclosed by membranes or meninges composed chiefly of connective tissue. The developing nervous system of embryos and young animals is highly radiosensitive because the actively proliferating and developing primitive neuron precursors and neuroglial cells are relatively sensitive to the direct cytocidal actions of radiation. In the mature central nervous system, with its relatively radioresistant parenchymal cells and neuroglial cells, the radiation doses required to cause early destruction of many of these cells are very large.
