1. 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 mcm. In contrast to dendrites, which rarely exceed 1.5 mm in length, axons can extend great distances from the parent cell body (some axons of the pyramidal tract are 40–50 cm long). Axons that are 0.5 mcm thick or more are generally enveloped by a segmented myelin sheath provided by oligodendroglia cells (in the brain and spinal cord) or Schwann cells (in peripheral nerves). Like dendrites and nerve cell bodies, axons contain many neurofibrils. With some exceptions, nerve cells synaptically transmit impulses to other nerve cells or to effector cells (muscle cells or gland cells) exclusively by way of the synaptic terminals of their axons.
2. In neurology and other clinical work, the term axon is also used as meaning dendrites (q.v.), which term is seldom used clinically.
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