From the Guidelines
The myelin sheath is produced by specialized glial cells, specifically oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system, through a process called myelination. This process involves the wrapping of glial cell plasma membranes around nerve axons multiple times, creating concentric layers of cell membrane rich in lipids 1. The most recent and highest quality study on this topic is from 2018, which highlights the importance of oligodendrocytes in myelination and the potential for using human iPSC-derived neurons to study myelination disorders 1.
Myelination Process
During myelination, the glial cell wraps around the axon, squeezing out cytoplasm and leaving compact layers of cell membrane that form the myelin sheath. This insulating layer is crucial for proper nerve function, as it increases the speed of nerve impulse transmission through saltatory conduction, where the electrical signal jumps between gaps in the myelin called nodes of Ranvier, making neural communication more efficient.
Key Players in Myelination
- Oligodendrocytes: responsible for myelin production in the central nervous system, with each oligodendrocyte capable of myelinating multiple axon segments 1.
- Schwann cells: perform this function in the peripheral nervous system, with each Schwann cell myelinating only one segment of a single axon.
- Glial cells: play a critical role in supporting neuronal function and can significantly alter neuronal activity and efficacy of experimental therapeutics in vitro 1.
Clinical Implications
Understanding the process of myelination and the role of glial cells is essential for developing effective treatments for myelination disorders, such as multiple sclerosis. The use of human iPSC-derived neurons and oligodendrocytes in co-culture systems can provide a valuable tool for studying these disorders and testing potential therapeutics 1.
From the Research
Myelin Sheath Production
The production of the myelin sheath is a complex process involving various cell types and mechanisms.
- In the central nervous system (CNS), myelin is produced by oligodendrocytes, while in the peripheral nervous system (PNS), it is produced by Schwann cells 2, 3, 4.
- The process of myelination involves the extension and modification of plasma membranes from these glial cells, which then wrap around axons to form a multilayered membrane structure 3, 5.
- The myelin sheath is composed of various lipids and proteins, including proteolipid protein (PLP) and myelin basic protein (MBP), which are essential for its structure and function 2, 6.
- The formation of myelin involves a series of coordinated cell-cell interactions and changes in plasma membrane architecture, including the compaction of opposing extracellular layers of membrane and the extrusion of cytoplasm from the intracellular domain of the sheath 3.
Key Components and Mechanisms
- Glycoproteins, such as protein zero (P0) and peripheral myelin protein-22 (PMP-22), play important roles in the formation and maintenance of myelin sheaths 6.
- The myelin-associated glycoprotein and the myelin-oligodendrocyte glycoprotein are also involved in glia-axon interactions and are potential targets for autoimmune demyelinating diseases such as multiple sclerosis 6.
- The process of remyelination, which occurs after demyelination, involves the recruitment and differentiation of oligodendrocyte precursor cells (OPCs) and the re-expression of myelin genes such as PLP and MBP 2, 5.