The myelin sheath

Myelin and Nodes of Ranvier

• Some axons are myelinated, meaning they have a myelin sheath around them.

  • Myelin is formed by the membrane of oligodendrocytes or Schwann cells wrapping around the axon.

• There are gaps in the myelin sheath called the nodes of Ranvier.

Importance of Myelin

• Myelin acts as an insulator.

• The insulation prevents ion leakage and signal degradation.

• Because of myelin, sodium channels are only needed at the nodes of Ranvier.

• The signal is propagated at the nodes of Ranvier.

Regions Around the Nodes

• Node of Ranvier:

  • High concentration of sodium channels.

  • This is where action potentials are propagated.

• Paranode Region:

  • Located next to the node.

  • Contains proteins that attach to the myelin to hold it in place along the axon.

• Juxtaparanode Region:

  • Located next to the paranode region.

  • Contains potassium channels for repolarization.

Organization and Channel Stability

• Sodium channels are confined to the node due to attachment proteins in the paranode region.

• Potassium channels are also restricted in their location due to the paranode structure.

Saltatory Conduction

• In myelinated axons, the signal "jumps" from node to node.

• This type of propagation is called saltatory conduction.

• Propagation only needs to occur at the nodes, which speeds up the signal transmission.