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  1. Raymond J. Colello

Published Online: 30 JAN 2010

DOI: 10.1002/9780470479216.corpsy0574

Corsini Encyclopedia of Psychology

Corsini Encyclopedia of Psychology

How to Cite

Colello, R. J. 2010. Myelin. Corsini Encyclopedia of Psychology. 1.

Author Information

  1. Virginia Commonwealth University

Publication History

  1. Published Online: 30 JAN 2010


Myelin is a protein and lipid-rich substance that is produced by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Myelin is elaborated into a sheath and wrapped, in a concentric fashion, around an axon. The deposition of myelin in a spiraling pattern around an axon generates two morphological features of the myelin sheath: the major dense line (DL) and the intraperiod line (IL). The DL is formed when the cytoplasm within the myelin process is lost, and the apposing plasma membranes come together. As the myelin sheath spirals around the axon, the outer faces of the plasma membrane of each wrap oppose each other to form the IL. The ensheathment of an axon with myelin is not continuous along its length, but is laid down as segments of myelin (internodes) that are interrupted, at regular intervals, by areas devoid of myelin, which are termed the nodes of Ranvier.