Schwann cells (otherwise, myelocytes or neurolemmocytes) belong to the neuroglia of the peripheral nervous system, where they are accompanied by long processes of neurons as auxiliary structures. In functional terms, they are analogues of oligodendrocytes present in the central nervous system. Schwann cells are located near the axons, forming the membrane of the peripheral nerve pathways.
Myelocytes were first characterized in 1838 by the German physiologist Schwann, in whose honor they received the name.
general characteristics
Along with mantle gliocytes, lemmocytes are the main elements of peripheral glia and are very similar to oligodendrocytes accompanying axons. However, there is still a slight difference between them, primarily in the location of the Schwann cells. The latter accompany PNS fibers, and oligodendrocytes are in the gray and white matter of the central nervous system. However, in some classifications, peripheral glia cells are considered oligodendroglia species.
The difference of Schwann cells is also that they cover only one axon, and oligodendrocyte - several at once. According to the type of membrane formed, neurolemmocytes are of two types - myelin and non-myelin, which form peripheral fibers of the corresponding species.
Myelocytes are located along the conducting cylinder. Schwann cells seem to braid the fiber, forming covered segments, between which Ranvier intercepts are located.
Structural features
The cytological features of lemmocytes include:
- poorly expressed synthetic apparatus (EPS and plate complex);
- poorly developed mitochondria;
- dark-colored nuclei.
The length of the Schwann cell varies from 0.3 to 1.5 mm.
Functions
Schwann cells play a supporting role in maintaining the functioning of the nerve fiber. At the same time, they perform 5 main functions:
- supporting - a network of lemmocytes form a supporting structure for neurons and their processes;
- trophic - various nutrients come from the lemmocytes to the processes;
- regenerative - lemmocytes are involved in the restoration of damaged nerve fibers;
- protective - nerve processes formed around axial cylinders provide additional resistance to damage;
- insulating (only for myelinated fibers) - the myelin layer prevents the exit of an electrical signal beyond the boundaries of a particular nerve process.
Schwann cells play a huge role in repairing damaged nerve fibers. With axon rupture, 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 again formed inside this channel.