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axon (ak´son)

The single process of a nerve cell that under normal conditions conducts nervous impulses away from the cell body and its remaining processes (dendrites). It is a relatively even filamentous process varying in thickness from about 0.25 to more than 10 mum. In contrast to dendrites, which rarely exceed 1.5 mm in length, a.'s can extend great distances from the parent cell body (some a.'s of the pyramidal tract are 40 to 50 cm long). A.'s 0.5 mum thick or over are generally enveloped by a segmented myelin sheath provided by oligodendroglia cells (in brain and spinal cord) or Schwann cells (in peripheral nerves). Like dendrites and nerve cell bodies, a.'s contain a large number of neurofibrils. With some exceptions, nerve cells synaptically transmit impulses to other nerve cells or to effector cells (muscle cells, gland cells) exclusively by way of the synaptic terminals of their a. [G. axon, axis]


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