Fig. 3.4. A longitudinal section though a node of Ranvier of the myelinated nerve fiber in layer 4C of the primary visual cortex from a 27 year old monkey. At the node the axolemma has a dense undercoating. On each side of the node are the paranodes, where the myelin lamellae gradually terminate in a helical fashion, the inner lamellae terminating first. As the lamellae terminate the dense line of the sheath opens up to enclose a helix of cytoplasm, which in longitudinal sections appears as a series of pockets (arrows) on each side of the axon. As already noted, at paranodes the axolemma and the plasma membrane of the sheath come close together to form a junction.
