The myelin sheath is the insulating coating that protects your nerves and helps them quickly and efficiently send signals throughout your body. When the myelin coating is damaged, it can cause various medical conditions that slow or stop the transmission of these signals. Myelin ensheaths part of an axon known as an internodal segment, in multiple myelin layers of a tightly regulated internodal length. The ensheathed segments are separated at regular short unmyelinated intervals, called nodes of Ranvier. Each node of Ranvier is around one micrometre long. Myelin sheath formation In the peripheral nervous system (PNS), myelination is preceded by invasion of the nerve bundle by Schwann cells, rapid multiplication of these cells and segregation of the individual axons by Schwann cell processes. Smaller axons (≤1 μm), which will remain unmyelinated, are segregated; several may be enclosed in one cell, each within its own pocket. Large axons (≥1 μm) destined for myelination are enclosed singly, one cell per axon per internode. These cells ... Each myelin-generating cell furnishes myelin for only one segment of any given axon. The periodic interruptions where short portions of the axon are left uncovered by myelin are the nodes of Ranvier, and they are critical to the functioning of myelin.
