Nodes, paranodes, and incisures: from form to function.

  • Scherer S
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Abstract

The exquisite molecular architecture of myelinated fibers is the basis for saltatory conduction. The nodal axolemma contains high concentrations of voltage-dependent sodium channels as well as the cell adhesion molecules neurofascin and Nr-CAM, all of which are probably linked to the axonal cytoskeleton by ankyrin. At paranodes, the axonal membrane contains paranodin/Caspr, which may be a Ca(2+)-dependent cell adhesion molecule with a heterophilic partner on the apposed glial cell membrane. The juxtaparanodal axonal membrane contains the potassium channels Kv1.1 and Kv1.2, as well as the associated beta 2 subunit, which together may function to dampen re-entrant excitation. The paranodes and incisures of the Schwann cell myelin sheath contain "reflexive" adherens junctions and gap junctions. The adherens junctions are composed of E-cadherin as well as alpha- and beta-catenin, which together probably join the adjacent layers of noncompact myelin together. Reflexive gap junctions, comprising connexin32 and at least one other connexin protein, form a radial pathway for the diffusion of ions and small molecules directly across the myelin sheath.

Author-supplied keywords

  • Animals
  • Axons
  • Axons: physiology
  • Cell Adhesion Molecules
  • Cell Adhesion Molecules: physiology
  • Gap Junctions
  • Gap Junctions: physiology
  • Gap Junctions: ultrastructure
  • Humans
  • Membrane Glycoproteins
  • Membrane Glycoproteins: physiology
  • Myelin Sheath
  • Myelin Sheath: physiology
  • Myelin Sheath: ultrastructure
  • Nerve Growth Factors
  • Nerve Growth Factors: physiology
  • Neural Cell Adhesion Molecules
  • Neural Cell Adhesion Molecules: physiology
  • Neural Conduction
  • Neuropeptides
  • Neuropeptides: physiology
  • Ranvier's Nodes
  • Ranvier's Nodes: physiology
  • Ranvier's Nodes: ultrastructure

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Authors

  • S S Scherer

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