The myelin sheath is a fatty coating that wraps around nerve fibers, insulating them so electrical signals travel faster and more efficiently through your nervous system. Without it, the signals your brain sends to move a hand or feel a texture would arrive slowly, weakly, or not at all. Myelin is one of the most important structures in your body that most people never think about until something goes wrong with it.
What Myelin Is Made Of
Myelin is unusually rich in fat. Its dry weight is 70 to 85 percent lipid, with only 15 to 30 percent protein. That high fat content is what gives it its insulating properties, much like the rubber coating around an electrical wire. The white color of myelin is also why certain brain regions are called “white matter.”
Two proteins do most of the structural work: myelin basic protein (MBP), which compacts the layers of myelin tightly together, and proteolipid protein (PLP), which helps anchor the membrane. These two are the dominant proteins in human myelin, and versions of them appear across a wide range of species, suggesting they’ve been essential for a very long time in evolutionary terms.
How Your Body Builds It
Different cells produce myelin depending on where in the nervous system you look. In the brain and spinal cord (the central nervous system), cells called oligodendrocytes do the job. A single oligodendrocyte can extend multiple arms, each wrapping a segment of a different nerve fiber. In the nerves running through your limbs and organs (the peripheral nervous system), Schwann cells handle myelin production instead, with each Schwann cell wrapping a single segment of a single nerve fiber.
Myelin doesn’t coat a nerve fiber in one continuous sheet. It wraps in segments, leaving tiny gaps between each section. These gaps, called nodes of Ranvier, are critical to how myelinated nerves work.
Why It Makes Signals Faster
An electrical signal traveling along an unmyelinated nerve fiber moves continuously, like a flame creeping along a fuse. That’s slow. Unmyelinated fibers conduct signals at roughly 1 meter per second. Myelinated fibers of the same diameter conduct signals about 10 times faster, with some large myelinated fibers reaching speeds around 15 meters per second or more.
The speed boost comes from a process called saltatory conduction. Under the myelin-covered sections, the insulation prevents electrical charge from leaking out through the membrane, so the signal shoots rapidly through the interior of the nerve fiber. But the signal weakens as it travels, so it needs to be refreshed. That’s what the nodes of Ranvier are for. Each node is packed with voltage-sensitive sodium channels that regenerate the electrical impulse at full strength. The signal essentially jumps from one node to the next, skipping the insulated segments entirely. This jumping pattern is far more energy-efficient than continuous conduction, because only the small nodal areas need to actively fire.
Myelin Does More Than Insulate
For decades, myelin was understood purely as insulation. Recent research has revealed it plays a more active role. Myelin sheaths contain the full set of enzymes needed to break down glucose and produce energy (ATP) independently of the cell’s main power plants, the mitochondria. That energy doesn’t just serve the myelin itself. The sheath layers are connected to the inner nerve fiber through tiny protein channels called connexins, creating a possible route for transferring ATP directly from the myelin to the nerve fiber it surrounds.
Myelin also carries its own set of protective enzymes, including ones that neutralize damaging oxygen-based molecules (free radicals). This means myelin acts as both a fuel supplier and a shield, helping keep the nerve fiber healthy and functional beyond simply speeding up its signals.
What Happens When Myelin Is Damaged
When myelin breaks down, a process called demyelination, nerve signals slow dramatically, arrive garbled, or fail to conduct at all. The most well-known demyelinating disease is multiple sclerosis (MS), in which the immune system mistakenly attacks myelin in the brain and spinal cord.
During an MS relapse, inflammation strips myelin from nerve fibers and disrupts signal conduction. This produces what neurologists call “negative symptoms”: loss of function rather than added sensations. Paralysis, numbness, and vision loss during relapses are largely caused by this conduction block. Even in partially demyelinated fibers, the ability to carry rapid trains of signals degrades, which contributes to weakness and sensory problems that can persist between relapses.
MS is not the only condition that damages myelin. Guillain-Barré syndrome attacks myelin in the peripheral nervous system. Vitamin B12 deficiency can impair myelin maintenance. And insufficient vitamin D levels, particularly during adolescence, appear to increase the risk of developing MS later in life.
How Your Body Repairs Myelin
Your nervous system does have a natural repair process. After myelin is damaged, precursor cells (essentially stem cells committed to becoming myelin-producing cells) shift into a reactive state. They begin multiplying and migrating toward the injury site, drawn by growth factors released from the damaged area. Once they arrive, these precursor cells mature into new oligodendrocytes that wrap fresh myelin around the bare nerve fibers.
This process, called remyelination, requires a precise sequence. The precursor cells must first be activated, then reach the right location, then fully differentiate into mature myelin-producing cells. A key transcription factor called myelin regulatory factor (MyRF) drives the final step, switching on the genes that produce myelin proteins and allowing the new sheath to compact properly around the nerve fiber.
The problem is that remyelination often stalls, especially in chronic conditions like MS. Precursor cells may reach the damaged area but fail to mature. The reasons are complex and still being studied, but this bottleneck is one of the biggest obstacles to recovery from demyelinating diseases. These precursor cells also serve other roles during injury: they help form protective scar tissue, modulate inflammation, and can even present pieces of foreign material to immune cells, making them far more versatile than simple repair units.
Nutrients That Support Myelin Health
Because myelin is so lipid-rich, its production and maintenance depend on adequate fat and micronutrient intake. Vitamin B12 is essential for myelin synthesis, and deficiency can cause neurological symptoms that mimic demyelinating disease. Vitamin D levels matter too, with evidence suggesting that low levels, particularly during adolescence, increase the risk of MS.
Some dietary patterns show limited but promising associations with myelin health. Higher intake of fish and polyunsaturated fatty acids may reduce risk or influence the progression of MS. Caloric restriction and fasting-mimicking diets have also shown some early signals of benefit, though the evidence remains limited. Adolescent obesity is another risk factor for MS, reinforcing the broader connection between metabolic health and myelin integrity.
Treatments Aimed at Rebuilding Myelin
Most current MS treatments work by suppressing the immune attack, but they don’t rebuild what’s already been lost. A new generation of therapies is focused specifically on promoting remyelination. Clemastine, an older antihistamine, is one of the most actively studied candidates, with multiple clinical trials testing it alone and in combination with metformin (a diabetes drug that may help aging precursor cells regain their ability to mature). Other approaches in clinical testing include drugs that block specific receptors to nudge precursor cells toward maturation, antibodies targeting proteins that inhibit myelin repair, and even testosterone, which appears to have protective effects on myelin.
None of these remyelination therapies have reached widespread clinical use yet, but the breadth of approaches being tested reflects how central myelin repair has become in neurological research. The goal is not just to stop damage but to reverse it, restoring conduction in nerve fibers that have been stripped bare.