Schwann cells (otherwise myelocytes or neurolemmocytes) refer to the neuroglia of the peripheral nervous system, where they accompany the long processes of neurons as auxiliary structures. In functional terms, they are analogues of oligodendrocytes present in the CNS. Schwann cells are located near axons, forming sheaths of peripheral nerve pathways.
Myelocytes were first characterized in 1838 by the German physiologist Schwann, after whom they were named.
General characteristics
Along with mantle gliocytes, lemmocytes are the main elements of peripheral glia and are very similar to the oligodendrocytes accompanying axons. However, there are still some differences between them - primarily in where the Schwann cells are located. The latter accompany the fibers of the PNS, and oligodendrocytes are found in the gray and white matter of the central nervous system. However, in some classifications, peripheral glial cells are considered varietiesoligodendroglia.
The difference between Schwann cells is also that they cover only one axon, and the oligodendrocyte - several at once. According to the type of sheath formed, neurolemmocytes are of two types - myelinated and non-myelinated, which form peripheral fibers of the corresponding types.
Myelocytes are located along the conducting cylinder. Schwann cells seem to braid the fiber, forming sheathed segments, between which there are nodes of Ranvier.
Building features
The cytological features of lemmocytes include:
- poorly defined synthetic apparatus (EPS and lamellar complex);
- poorly developed mitochondria;
- dark colored kernels.
The length of the Schwann cage varies from 0.3 to 1.5 mm.
Functions
Schwann cells play an auxiliary role in maintaining the functioning of the nerve fiber. At the same time, they perform 5 main functions:
- support - a network of lemmocytes form a supporting structure for neurons and their processes;
- trophic - various nutrients come from lemmocytes to the processes;
- regenerative - lemmocytes are involved in the restoration of damaged nerve fibers;
- protective - neural processes formed around the axial cylinders provide additional resistance to damage;
- insulating (only for myelinated fibers) -- myelin layer prevents exitelectrical signal outside of a specific nerve process.
Schwann cells play a huge role in the restoration of damaged nerve fibers. When an axon ruptures, lemmocytes first phagocytize the damaged particles, and then multiply and form a bridge connecting the adjacent ends of the process. Then an axial cylinder is formed again inside this channel.
