Myelin, what it is and what its function is

Myelin, what it is and what its function is

Myelin is a white fatty substance that surrounds the axon of some nerve cells, forming an insulating layer. It is essential for the proper functioning of the nervous system. It is a part of a kind of glial cell.


  • 1 What is myelin
  • 2 What is myelination
  • 3 Myelin Function
  • 4 Myelin Disorders or Demyelination
  • 5 Schizophrenia, bipolar disorder and myelin
  • 6 Symptoms of demyelination
  • 7 Myelin Repair

What is myelin?

Neurons are the cells of the nervous system and thanks to them we are able to think, see, hear, speak, feel, move ... Each neuron is made up of a cell body and an axon (the extension of the cell body that carries the messages). Most axons in the central nervous system are wrapped in myelin, a substance rich in lipids (fatty substances) and proteins. Like the coating of an electric cable, myelin insulates and protects the axon and helps accelerate nerve transmission.

Myelin is present in the central nervous system (CNS) and the peripheral nervous system (SNP). CNS myelin is produced by special cells called oligodendrocytes. Myelin SNP is produced by Schwann cells. The two types of myelin are chemically different, but both perform the same function: promote the efficient transmission of a nerve impulse along the axon.

What is myelination?

The production of the myelin sheath is called myelination or myellogenesis. In humans, myelination begins early, during the third trimester of pregnancy, although there is little myelin in the brain at birth. During childhood, myelination occurs rapidly, which in turn leads to the rapid development of the child, which includes crawling and walking during the first year. Myelination continues during the adolescent stage of life.

Myelin Function

The main objective of a myelin sheath is increase the speed at which impulses propagate along myelinic fiber. Along the unmyelinated fibers, the impulses move continuously like waves, but in the myelinated fibers, they "jump" or propagate by saltatory conduction. Myelin decreases capacitance and increases electrical resistance across the cell membrane (axolema). Therefore, myelination prevents electrical current from leaving the axon. It is believed that myelin allows for greater body size while maintaining agile communication between distant parts of the body.

Schwann cells supply myelin for the peripheral nervous systemwhile the oligodendrocytes, specifically of the interfascicular type, myelinize the axons of the central nervous system. Myelin is considered a defining characteristic of vertebrates, but myelin-like sheaths have also been observed in some invertebrates, although they are quite different from vertebrate myelin at the molecular level.

The most important function of the myelin sheath is therefore accelerate depolarization throughout the axon, avoiding sodium filtration, maintaining a strong load difference between inside and outside the axon. In a way, it helps the signals move quickly directly. Because the neurons are so tight (especially in the brain, where space is limited, but needs to process so much information), they are always in contact with each other.

What would happen if axons without the rubber wrap were touched? Well, our body would be a chaotic disaster. Thanks to the grease cover that insulates electricity, we send the right impulses to the right place, quickly and efficiently. In addition, our neurons are not damaged by the constant flow of electrical impulses due to this sheath, such as wire with rubber, which does not burn as easily as it does not.

Myelin Disorders or Demyelination

Demyelination is the loss of the myelin sheath that insulates nerves and it is what characterizes some neurodegenerative autoimmune diseases, such as multiple sclerosis, acute disseminated encephalomyelitis, optic neuromyelitis, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Canavan disease, Guillain-Barré syndrome, central pontine myelinosis and even schizophrenia and bipolar disorder. There are also congenital demyelinating diseases such as leukodystrophy and Charcot-Marie-Tooth disease.

Patients with pernicious anemia can also suffer serious neuronal damage. The degeneration of the spinal cord secondary to pernicious anemia, it can cause damage to the peripheral nerves of the central nervous system, affecting speech, balance and cognitive awareness. When myelin degrades, the conduction of signals along the nerve can be affected or lost, and the nerve eventually withers.

Schizophrenia, bipolar disorder and myelin

Have been found neuronal axon and myelin abnormalities in patients with schizophrenia and bipolar disorder, compared to healthy individuals. More specifically, a reduction of myelin was observed in neurons of white matter, as well as an abnormal diffusion of N-acetyl aspartate, a metabolite that is found within nerve cells.

Apparently, both bipolar disorder and schizophrenia have common causes, even if they are two different diseases. The reduction in myelin production is the most likely cause of the genesis of both diseases, only that the anomalies take different paths. It is believed that this deficit is causing oligodendrocytes, that produce less myelin than necessary by not receiving enough energy. But the causes of this disorder are still to be clarified.

Symptoms of demyelination

Demyelination produces various symptoms depending on the functions of the affected neurons. The signals between the brain and other parts of the body are interrupted, so the symptoms differ depending on the affected areas.

The symptoms can be:

  • Vision / hearing loss
  • Double vision
  • Blurred vision in the central visual field that affects only one eye, may be accompanied by pain in eye movement
  • Weird sensation in legs, arms, chest or face, such as tingling or numbness (neuropathy)
  • Weakness in arms or legs
  • Speech impairment and memory loss
  • Heat sensitivity (symptoms worsen or reappear when exposed to heat, such as a hot shower)
  • Difficulty coordinating movement or balance
  • Difficulty controlling bowel movements or urination
  • Fatigue
  • Tinnitus or tinnitus (internal sounds in the ear)

Myelin Repair

Research on the possible repair of damaged myelin sheaths is ongoing. Some techniques include surgically implanting oligodendrocyte precursor cells in the central nervous system and inducing myelin repair with certain antibodies. While the results in mice have been encouraging (through stem cell transplantation), it is still unknown if this technique can be effective in replacing myelin loss in humans.

On the other hand, cholinergic treatments, such as acetylcholinesterase inhibitors (AChEI), can have beneficial effects on myelination, repairing it. The increase in cholinergic stimulation can also act through subtle trophic effects in brain development processes and, in particular, in oligodendrocytes and the myelination process. By increasing the cholinergic stimulation of oligodendrocytes, AChEI and other cholinergic treatments could possibly promote myelination during the development and repair of myelin in old age.



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