myelin sheath adaxonal region

Definition

Target type: cellularcomponent

The region of the myelin sheath nearest to the axon. [GOC:BHF, PMID:20237282]

The myelin sheath adaxonal region is a specialized cellular compartment located at the interface between the myelin sheath and the axonal membrane. It is characterized by a unique structural organization and molecular composition, which contribute to its essential role in maintaining the integrity and function of the myelinated axon.

The adaxonal region is formed by the innermost layer of the myelin sheath, which is directly apposed to the axonal membrane. This layer, known as the adaxonal membrane, is a specialized domain of the myelinating glial cell plasma membrane. In the central nervous system (CNS), oligodendrocytes form the myelin sheath, while Schwann cells are responsible for myelination in the peripheral nervous system (PNS).

The adaxonal membrane is enriched in specific proteins and lipids that play crucial roles in the formation, stability, and function of the myelin sheath. These include:

- **Adhesion molecules:** Such as contactin, neurofascin, and L1CAM, which mediate the adhesion between the myelin sheath and the axon, ensuring their close apposition and preventing the diffusion of molecules between the two compartments.
- **Ion channels and pumps:** Such as potassium channels and sodium pumps, which regulate the ion gradients across the adaxonal membrane and contribute to the maintenance of axonal excitability.
- **Signaling molecules:** Such as growth factors and neurotrophins, which are involved in the regulation of axonal growth, survival, and function.
- **Lipid-modifying enzymes:** Such as myelin-associated glycoprotein (MAG) and myelin basic protein (MBP), which contribute to the formation and stability of the myelin sheath by modifying the lipid composition of the adaxonal membrane.

The adaxonal region is also characterized by the presence of a unique cytoskeleton, which provides structural support and regulates the organization of the adaxonal membrane. This cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments, which are linked to the axonal membrane and the myelin sheath through specialized protein complexes.

The adaxonal region plays a critical role in the function of the myelinated axon by:

- **Maintaining the integrity of the myelin sheath:** The close apposition between the adaxonal membrane and the axonal membrane prevents the diffusion of molecules and the disruption of the myelin sheath.
- **Regulating axonal excitability:** The ion channels and pumps in the adaxonal membrane contribute to the maintenance of the axonal membrane potential and the propagation of nerve impulses.
- **Providing metabolic support to the axon:** The adaxonal region serves as a conduit for the transport of nutrients and other essential molecules from the myelinating glial cell to the axon.
- **Facilitating axonal regeneration:** In the event of axonal injury, the adaxonal region plays a critical role in the repair and regeneration of the axon.

In summary, the myelin sheath adaxonal region is a highly specialized and dynamic cellular compartment that plays a crucial role in the maintenance and function of the myelinated axon. Its unique structural organization, molecular composition, and associated functions are essential for the proper conduction of nerve impulses and the overall health of the nervous system.'
"

Proteins (2)

Compounds (2)