Ranvier lace ring
definition
A Ranvier lace ring is a ring-shaped interruption of the fat or myelin sheath that surrounds nerve fibers. In the course of the "saltatory conduction of excitation" it serves to increase the speed of nerve conduction.
Saltatorisch, from Latin: saltare = to jump denotes the "jump" of an action potential that takes place when it hits a Ranvier cord as it spreads along the axon (a sheathed nerve fiber).
function
Have different nerve fibers different excitation conduction speeds. So they have special fast A-alpha nerve fibersthat direct their impulses to the skeletal muscles, a speed of just under 120 m / s, i.e. over 400 km / h! This fast forwarding is only possible by using the Action potential jumps from time to time, more precisely, always from one Ranvier lace ring to the next. Quasi like a sprinter who also makes long jumps during his sprint. The Ranvier lacing rings are located at regular intervals of 0.2 - 2mm on the axon, between two Schwann cells. These cells make up the Myelin sheath, a high-fat layer which the Nerve fiber enveloped and insulated.
In the area of a Ranvier lace ring is the density on voltage-dependent sodium channels especially high. An incoming signal (i.e. action potential) from the one in front Ranvier lace ring is caused by the strong influx of sodium from the outside into the nerve processed, amplified and immediately forwarded until it hits the next ring. There the same game starts all over again. The section between the lace-up rings only serves as a relay section and is therefore well insulated. The lace ring works like a Amplifier on the nerve fiber.
Demyelination
As Demyelination is called the Loss of the myelin sheath between the Ranvier lace-up rings. Although there is still a transmission of the action potential on the lace ring, this is above a certain degree of the disease too weakto reach the next lace ring. That is because the distance between the laced rings no longer myelinated (i.e. isolated). Known demyelinating diseases are multiple sclerosis or the diabetic neuropathy ("Diabetic foot").
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