Chapter 4 - Functional Organization of the Nodes of Ranvier

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This chapter reviews the molecular architecture of the nodes of Ranvier. The recent advances in the molecular anatomy of myelinated axons highlight several functional issues. One of the most surprising is that peripheral nervous system (PNS) myelin sheaths do not mainly act as electrical insulators of axons. The radial pathway for ion diffusion formed by gap junctions is not compatible with this common view and reducing capacitance is the likely role of myelin sheaths. Second, the intricate organization of the nodal, paranodal, juxtaparanodal, and internodal axonal domains relate closely to the organization of the myelin sheath itself. Although the details are still incomplete, the emerging evidence indicates that a molecular dialogue between myelinating glial cells and axons results in the local differentiation of their complementary cellular domains. Finally, the organization of the axonal membrane is disrupted by a number of mutations and disease processes that affect myelin sheaths, with functional consequences that are beginning to make sense.

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