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Myelinated retinal nerve fiber layers (MRNF) are retinal nerve fibers anterior to the lamina cribrosa that, unlike normal retinal nerve fibers, have a myelin sheath. Clinically, they appear to be gray-white well-demarcated patches with frayed borders on the anterior surface of the neurosensory retina.
Myelin Sheath. The myelin sheath is a protective membrane that wraps around part of certain nerve cells. Myelin also affects how fast signals travel through those nerve cells. Several diseases and conditions — multiple sclerosis being the most well-known — damage or destroy myelin.
Myelination is the formation of a myelin sheath. This article will discuss the structure and histology of myelin sheaths, their function, and the process of brain myelination. Contents. Overview. Myelination. Schwann cells. Oligodendrocytes. Myelin sheath function. Brain myelination. Clinical aspects. Demyelination. Schwannoma. Sources. + Show all.
The main purpose of myelin is to increase the speed at which electrical impulses (known as action potentials) propagate along the myelinated fiber. In unmyelinated fibers, action potentials travel as continuous waves, but, in myelinated fibers, they "hop" or propagate by saltatory conduction.
An example of the advantage of myelination is obtained by comparison of two different nerve fibers, both of which conduct at 25 m/sec at 20°C. The 500-mm diameter unmyelinated giant axon of the squid requires 5,000 times as much energy and occupies about 1,500 times as much space as the 12-mm diameter myelinated nerve in the frog.
Structure of the myelinated nerve fiber. (A) Illustration of myelinated nerve fiber and saltatory conduction of action potential. An example of PNS myelinated nerve fiber is shown....
The myelinated nerve fiber is designed by evolution to provide the body with a rapid and efficient transfer of information from peripheral receptors to the central nervous system (CNS), from the CNS to peripheral effectors, and between different centers within the CNS.
Intriguingly, in normally unmyelinated fibers, forced expression of neuregulin 1 type III in the postganglionic fibers of sympathetic neurons grown in culture can be forced to myelinate.
Myelin is the compaction of the plasma membrane of glial cells in a discontinuous spiral pattern over axons that form the myelinated central or peripheral nerve fibers. For this reason, these highly specialized and complex three-dimensional structures are also known as myelin sheaths.
Myelinated nerve fibers refer to nerve fibers in the eye that have abnormal intraocular myelination anterior to the lamina cribrosa, often associated with visual field defects and retinal vascular abnormalities.