Myelin sheath gap

The Node of Ranvier [ Ravie ] - also Ranvier'scher constriction or Ranvier node called - is the exposed portion of an axon between two Schwann cells, which are wrapped around a nerve fiber. At this point, the continuity of the axon enveloping myelin sheath is interrupted.

Named is the Ranvier'sche constriction after the French anatomist Louis -Antoine Ranvier (1835-1922), first introduced in 1871 in the Academy ( Comptes rendus, 1871) and in March 1872 in his paper " Recherches sur l' histologie et la physio -celled the nerfs "in the Archives of Physiology Normal et pathologique (IV / 2 ( Mars 1872) pp.129 -149 ) described and illustrated: " Je me propose, dans ce mémoire de décrire une nouvelle disposition of the nerfs, que j'ai communiquée déjà et de rechercher quelles sont pour les tubes nerveux, les voies d' échange of matériaux de nutrition et de disassimilation " ( P.129 ).

Construction

Nodes of Ranvier have a length of about 1 micron and dive along the axon course to a distance of about 0.2-2 mm. Situated between two rings section is called the internode.

Nodes of Ranvier are important for rapid saltatory conduction. The action potential is not running continuously along the myelinated nerve fiber, but " jumps" from node to node. Between these the electrical excitation is passed elektrotonisch by the isolation of the myelin sheath.

The cell membrane in the area of ​​Schnürringe has a high density of voltage-gated sodium channels and can create a strong influx of Na during the depolarization.

The compound of glial ( oligodendrocytes and astrocytes in the central nervous system (CNS), Schwann cells in the peripheral nervous system (PNS ) ) and axon is closed at the sides of Schnürrings by paranodale septate junctions. In this way, a small enclosed space, the biochemical milieu can be well regulated and demarcated from the environment; Diffusion losses are minimized.

• Neurobiology
• Neurophysiology
• Nervous tissue