myelin sheath

The myelin sheath ( myelin sheath also, to Greek μυελός myelos, Mark ') provides an around the axons of nerve cells bearing vertebrate lipid-rich layer; they do is electrically insulating. In the central nervous system (CNS) will of oligodendrocytes, formed by the Schwann cells in the region of the peripheral nervous system (PNS ). It consists of the myelin sheath cells of each.

In the CNS, go from the soma of oligodendrocytes from projections, each of which envelop a portion of an axon. Therefore, may be involved in the myelin sheaths of axons about 10-50 a oligodendrocyte.

A Schwann cell in the PNS, however, always wrapped in only a portion of an axon, many Schwann cells lie one behind the other Soma with her around an axon. The Schwann cells grow with their soma during development of the myelin sheaths ( myelogenesis or marrow maturation ) depending on the type of nerve cell 3 - to about 50 times around the nerve process and wrap it around a while with several layers. Here, a membrane layer is located directly on the next. Between two protoplasmic, so the inner leaves of the cell membrane normally no more cytoplasm is present. They are fused together to the main line or internal attachment line. There is the Myelin Basic Protein. Not fused to the cell membranes at the locations of the so-called Schmidt- Lantermann notches or Myelininzisuren. These are the remnants of the cytoplasm, as visible by light microscopy narrow and oblique stripes through all the myelin layers of the myelin sheath dress and connected together for the exchange of material via gap junctions. After Ulrich Welsch also have the myelin sheaths of the CNS Schmidt- Lantermann notches.

The running in the myelin sheath myelinated nerve fibers are called, mark rich, myelinated or jacketed. The function of the myelin sheath is to protect the neurons against foreign action potentials and the rapid spread of excitation through the saltatory conduction. The servings of Neuronalaxone be interrupted at intervals of about 0.2 to 1.5 millimeters of the so-called Ranvier constriction rings. The section between two such constriction rings is in the peripheral nervous as corresponding to internode (or internodales segment) respectively.

Because myelin sheaths have an insulating effect, reduce the membrane capacitance and prevent leakage currents through the membrane. This elektrotone the spread of depolarization within the internode is faster and less loss than in unmyelinated nerves. The myelin sheath protects the axon just before action potentials from other neurons that happen to cross this neuron.

In multiple sclerosis and other demyelinating diseases, these same protective sheath of the nerve cells is destroyed - in the case of MS by autoantibodies such as anti- MOG antibody and anti -MBP antibodies. The corresponding process is known as demyelination.