The Myelin sheath

Myelin and Nodes of Ranvier

• Myelin is formed by the membrane of oligodendrocytes or Schwann cells wrapping around the axon.
• Gaps in the myelin sheath are called nodes of Ranvier.

Importance of Myelin

• Myelin acts as an insulator.
• It prevents ion leakage and signal degradation along the axon.
• Myelin reduces the need for sodium channels in myelinated regions.
• Signal propagation occurs only at the nodes of Ranvier.

Regions Around the Nodes of Ranvier

• Node:
  • High concentration of sodium channels.
  • Action potential propagation occurs here.
• Paranode:
  • Located next to the node.
  • Contains proteins that attach to the myelin, holding it in place along the axon.
• Juxtaparanode:
  • Contains potassium channels for repolarization.

Organization and Channel Stability

• Sodium channels are confined to the node due to attachment proteins in the paranode regions.
• Potassium channels are restricted to the juxtaparanode region.

Saltatory Conduction

• The signal "jumps" from node to node along the myelinated axon.
• Propagation of the signal (action potential) only occurs at the nodes, speeding up transmission.