Myéline

The Myéline is a substance made up mainly of lipids (Sphingomyéline) whose layers alternate with layers of protids. In a general way, the myéline is used to insulate and to protect nervous fibers, like the plastic around the electric wires does it.

This fatty substance is found in certain cells of the nervous systems: the cells of Schwann , located in the peripheral Nervous system (nerves), and in the Oligodendrocyte S , located in the central Nervous system (the brain).

The cells of Schwann coat the axones* with nervous fibers of the peripheral nervous system. On the level of many fibers (but not all), these cells are flattened and their plasmic membrane is rolled up around the axons. The cells of Schwann then form a long discontinuous sleeve called the “sheath of myéline”. The sheath of myéline makes it possible to increase the propagation velocity of the Nerve impulse along these nervous fibers, being able to go at a speed of 100m.s-1: indeed, between each myelinized part of the axon a part “with naked” of the axon is which, it, is conducting. One calls this place a Nœud of Ranvier. Thus, the impulse change of a node of Ranvier to the other along the axon, which enables him to traverse the same way in a less time. It is what one names “conduction saltatoire”. In the human body, this mode of conduction is used where the speed of an impulse must be fast. The nerves which move towards the skeletal muscles, for example, are made myelinized fibers with conduction saltatoire.

  • the axon is the very lengthened part of the neurons (the neurons are the cells which lead the nerve impulses). The nerves, for example, consist of several axons.

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