Molecular Genetics of Demyelination: New Wrinkles on an Old Membrane

Myelin is one of the fundamental adaptations of vertebrates. By limiting axonal depolarization to nodes of Ranvier, the periodic interruptions in myelin, it increases axonal conduction velocity. Its multilamellar structure results from the spiral wrapping of specialized cell membrane around an axon (Figure 1A). The apposed external surfaces of the membrane form the intraperiod lines, and the cytoplasmic proteins form the major dense line. These alternating intraperiod and major dense lines give myelin its characteristic appearance in electron micrographs (Figure 1B).