EM 403 Node of Ranvier

Node of Ranver

Transmission electron microscopy (TEM) of myelinated nerve fibers in the visual cortex.

Nodes of Ranvier are small gaps between segments of the myelin sheath that encircle the myelinated axons of neurons. A myelinated axon with a node of Ranvier runs diagonally across the image. The small, myelinated axon adjacent to the fiber is not part of the node.

• Oligodendrocytes (green) – from up to 50 segments along multiple axons
  • Internodal Segments (#1,#2; dark green) – long regions covered by myelin sheath
  • Paranodal Segments (#1,#2; light green) – lamellae terminate in sequential swellings on each side of the node
    • Seal the myelin sheath with the axon
    • Isolates the space between the axon and the myelin sheath from the extracellular environment at the node
  • Node – cell membrane of the axon is only covered by processes
• Nerve Fibers
  • Myelinated Axons (yellow)
  • Unmyelinated Axons (dark yellow)
• Dendritic Spines (light blue)
• Axon Terminals (orange) - form synapses with dendritic spines
  • Synaptic Vesicles (purple) - contain neurotransmitters
• Astrocytes (tan) - irregularly shaped processes

Subcellular Structures

• Mitochondria (red)
• Endoplasmic Reticulum (cyan)
• Microtubules (blue)

Courtesy of Alan Peters and Claire Folger Sethares, The Fine Structure of the Aging Brain (www.bu.edu/agingbrain), Boston University School of Medicine, Boston, MA.