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How do oligodendrocytes and Schwann cells form myelin sheaths?
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nervous system
In a myelinated axon, the myelin sheath prevents the local current (small black arrows) from flowing across the membrane. This forces the current to travel down the nerve fibre to the unmyelinated nodes of Ranvier, which have a high concentration of ion channels. Upon stimulation, these ion channels propagate the action potential (large green arrows) to the next node. Thus, the action potential jumps along the fibre as it is regenerated at each node, a process called saltatory conduction. In an unmyelinated axon, the action potential is propagated along the entire membrane, fading as it diffuses back through the membrane to the original depolarized region.
Oligodendrocytes and Schwann cells are specialized neuroglia responsible for producing myelin, an insulating sheath that surrounds axons to facilitate efficient nerve impulse transmission.12
While they perform similar functions, they operate in different parts of the nervous system:
- Oligodendrocytes: These cells are located in the central nervous system. To form the myelin sheath, an oligodendrocyte wraps itself around a length of an axon like a rolled sheet, creating several layers of insulation.1
- Schwann cells: These are the functional equivalents of oligodendrocytes found in the peripheral nervous system. They deposit myelin in layers around neuronal axons.132
In both systems, the resulting myelin sheath is not continuous; it is interrupted at regular intervals by gaps known as nodes of Ranvier. These nodes are essential for saltatory conduction, the process by which nerve impulses jump along the axon to increase the speed of signal transmission.12