Myelin
Say it: MY-uh-lin
Myelin is the fatty, layered sheath that glial cells wrap around many axons, insulating them so nerve impulses travel faster and more efficiently.
Definition
What is myelin?
Myelin is an insulating covering that glial cells build around axons by wrapping their own cell membrane around the axon many times. Because it is made of stacked membranes, myelin is rich in lipids, mainly phospholipids, along with proteins that hold the layers together. In the brain and spinal cord it is made by oligodendrocytes, each of which can sheath segments of several axons; in the peripheral nervous system each Schwann cell wraps a single segment of one axon.
The sheath is not continuous. Short bare gaps called nodes of Ranvier separate the wrapped segments, and voltage-gated channels cluster at these nodes. The action potential therefore jumps from node to node, a process called saltatory conduction that is much faster and uses less energy than conduction along a bare axon. Myelin's fat content also explains why regions packed with myelinated axons look pale and are called white matter.
Loss of or damage to myelin, called demyelination, slows or blocks nerve signals. In multiple sclerosis the immune system attacks myelin in the brain and spinal cord, while in Guillain-Barre syndrome it attacks myelin in peripheral nerves.
Word parts
Where does the word “myelin” come from?
- myel-
- marrowGreek myelos
- -in
- a chemical substancesuffix used in names of compounds
Practice it
Where you'll meet it
Related
Terms that go with it
- AxonAn axon is the single long projection of a neuron that carries electrical impulses away from the cell body toward other neurons, muscles or glands.
- Action potentialAn action potential is a brief, all-or-none reversal of the voltage across a nerve or muscle cell membrane that travels along the cell as a signal.
- NeuronA neuron is a nerve cell, the basic signaling unit of the nervous system, which receives information and passes it on as electrical and chemical signals.
- Central nervous systemThe central nervous system is the brain and spinal cord, the part of the nervous system that takes in sensory input, integrates it and sends out commands.
- AutoimmunityAutoimmunity is an immune response wrongly directed at the body's own healthy cells and tissues, and it is the cause of autoimmune diseases.
- LipidA lipid is one of a varied group of biological molecules, including fats, oils, phospholipids, waxes and steroids, that do not dissolve in water.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 12.2 Nervous Tissue
- OpenStax Biology 2e, 35.2 How Neurons Communicate
- NCBI MeSH: Myelin Sheath
- NCI Dictionary of Cancer Terms: myelin
Last updated
Spotted a mistake? Tell us and we'll correct it.
Practice Neuroscience
Free neuroscience quizzes, with an explanation for every answer.
See the Quizzes