myelin

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myelin

 [mi´ĕ-lin]
the lipid substance forming a sheath (the myelin sheath) around the axons of certain nerve fibers; it is an electrical insulator that serves to speed the conduction of nerve impulses in these nerve fibers, which are called myelinated or medullated fibers. adj., adj myelin´ic. 

Myelinated nerve fibers occur predominantly in the cranial and spinal nerves and compose the white matter of the brain and spinal cord. Unmyelinated fibers are abundant in the autonomic nervous system. The term gray matter refers to areas in the nervous system in which the nerve fibers are unmyelinated. In unmyelinated nerves impulses are conducted by the propagation of the action potential along the membrane of the axon. In myelinated nerves impulses are transmitted by an entirely different process, called saltatory conduction, in which the impulse jumps from one node of ranvier to the next. Impulses in myelinated nerves are transmitted hundreds of times faster and require much less energy than in unmyelinated nerves.
Structure of a typical myelin sheath. From Applegate, 2000.

my·e·lin

(mī'ĕ-lin),
1. The lipoproteinaceous material, composed of regularly alternating membranes of lipid lamellae (for example, cholesterol, phospholipids, sphingolipids, and phosphatidates) and protein, of the myelin sheath.
2. Droplets of lipid formed during autolysis and postmortem decomposition.

myelin

/my·elin/ (mi´ĕ-lin) the lipid-rich substance of the cell membrane of Schwann cells that coils to form the myelin sheath surrounding the axon of myelinated nerve fibers.myelin´ic

myelin

(mī′ə-lĭn) also

myeline

(-lĭn, -lēn′)
n.
A white fatty material, composed chiefly of lipids and lipoproteins, that encloses certain axons and nerve fibers. Also called medulla.

my′e·lin′ic adj.

myelin

[mī′əlin]
Etymology: Gk, myelos, marrow
a lipoproteinaceous substance constituting the sheaths of various nerve fibers throughout the body and enveloping the axis of myelinated nerves. It is largely composed of phospholipids and protein, which gives the fibers a white, creamy color. myelinic, adj.

my·e·lin

(mī'ĕ-lin)
1. The lipoproteinaceous material of the myelin sheath, composed of alternating membranes of lipid and protein.
2. Droplets of lipid formed during autolysis and postmortem decomposition.

myelin

The fatty, white material forming a sheath around most nerve fibres and acting as an insulator. See also DEMYELINATION.

myelin

a white phospholipid. See MYELIN SHEATH.

Myelin

A whitish fatty substance that acts like an electrical insulator around certain nerves in the peripheral nervous system. It is thought that the loss of the myelin surrounding the vestibular nerves may influence the development of Ménière's disease.

myelin (mī·ln),

n a white fatty material that constitutes the medullary sheath that surrounds some nerve fibers.
Enlarge picture
Myelin.

my·e·lin

(mī'ĕ-lin)
Lipoproteinaceous material, composed of regularly alternating membranes of lipid lamellae (e.g., cholesterol, phospholipids, sphingolipids, and phosphatidates) and protein, of the myelin sheath.

myelin (mī´əlin),

n a fatlike substance forming a sheath around certain nerve fibers. It is associated with volitional nervous system fibers and is believed to be related to the capacity of nerve structures for rapid transmission of nerve impulses. Various diseases, such as multiple sclerosis, can destroy these myelin wrappings.

myelin

1. the lipid substance forming a sheath around the axons of certain nerve fibers; these nerve fibers are spoken of as myelinated or medullated fibers.
2. lipoid substance found in various normal and pathological tissues, which differs from fats in being doubly refractive.
Myelinated nerve fibers occur predominantly in the cranial and spinal nerves and compose the white matter of the brain and spinal cord. It is the myelin sheath that gives the whitish color to the areas of white matter. Unmyelinated fibers are abundant in the autonomic nervous system.

Patient discussion about myelin

Q. What is Myelin?

A. As part of the nervous system, myelin lines nerve fibers to protect and insulate neurons. Myelin aids in the quick and accurate transmission of electrical current carrying data from one nerve cell to the next. When myelin becomes damaged, the process involves numerous health conditions, including multiple sclerosis.

Dysfunction in the myelin of nerve fibers causes the interruption of smooth delivery of information. Either nerve impulses can be slowed, such that we can't pull our hand away in time to avoid being burned, or mixed up, so we aren't able to determine if a pan is hot in the first place. This is akin to a pet chewing on a wire, causing the device to dysfunction. When problems arise in nerves of the PNS, neuropathy might result, and when injury affects the nerves of the CNS, multiple sclerosis is often diagnosed.

More discussions about myelin
References in periodicals archive ?
His group has undertaken a small double-blind pilot study in which people with early relapsingremitting MS were given specially prepared myelin proteins by mouth, daily, for one year.
Patient-specific MRTCs are expanded in culture with specific peptides identified by assaying peripheral blood mononuclear cell reactivity against peptides derived from the three myelin proteins.
The EAA measures proliferative responses of patient peripheral T-cells upon exposure to peptides of myelin proteins.
The reduction in autoantibodies targeting multiple myelin proteins indicates that BHT-3009 may produce a broad response in a heterogeneous population of MS patients.
We are delighted with the demonstration of tolerization of the immune system to myelin proteins in individuals with multiple sclerosis.
Steinman and his team have designed customized "cocktails" of the DNA that instruct a number of the relevant myelin proteins involved in such B cell responses to the disease.