Myelin forms sheaths that cover the axons of neurons.
Myelin is a system of phospholipid bilayers made up of sphingolipid , which enables the transmission of nerve impulses to the various body regions through an insulating effect, forming sheaths that are responsible for surrounding the axons of neurons.
Myelin is specifically constituted as a sphingophospholipid that is formed by sphingol , an alcohol composed of a choline, phosphate and fatty acid chain . In the spinal and cranial nerves , as well as in the peripheral nervous system ( PNS ), myelin sheaths develop thanks to Schwann cells that produce layers of proteins and lipids.
It is in the membrane of this type of small-volume cells where myelin is found: since the Schwann cells wind successively around the axons, they give rise to sheaths.
myelin sheath
The myelin sheath is responsible for wrapping the axon with the exception of the nodes of Ranvier (which are those places located between the myelin sheaths). Myelin functions as an electrochemical insulator that allows nerve impulses to be transmitted in hops from node to node.
The situation within the central nervous system ( CNS ) is different since, in this case, myelin is made up of oligodendrocytes (another class of cells that have numerous dendrites).
It is common to talk about white matter and gray matter in the brain . Myelin is responsible for the color of white matter, while those unmyelinated axons make up gray matter.
Myelin acts as an insulator.
Disorders and diseases
If a person, due to some disorder, loses myelin, they will suffer from major problems in their nervous system. The electrical impulses, in the absence of this substance, will not complete their journey or will circulate very slowly, as occurs with diseases such as multiple sclerosis .
However, it must also be emphasized that in addition to this aforementioned disease, other diseases can occur in the patient, such as amyotrophic lateral sclerosis, also called Charcot disease , which is characterized by being degenerative and which results in a progressive muscular paralysis that ends in death.
Likewise, other diseases that are caused by myelin are Baló's concentric sclerosis , which is neurological and occurs as a consequence of the rapid loss of the envelope that covers the aforementioned myelin, or leukodystrophies. The latter in particular also occur as a result of the degeneration of the former's fat and among its most frequent symptoms are visual or motor alterations.
Other conditions that affect myelin
And all this, without forgetting that there are other pathologies that are also directly related to myelin. This would be the case of central pontine myelinolysis , Devic syndrome or Marchiafava-Bignami disease. Corpus callosum atrophy syndrome is also known as this last pathology, which is a very rare encephalopathy.
People with chronic alcoholism are those who can be most affected by this disease, which results in a series of symptoms such as personality changes, seizures, hallucinations, voice changes, or notable deficiencies in intelligence. However, we can establish that there are two clearly differentiated types: one in which the damage is slight and one in which the patient will reach a coma or even suffer a state of stupor.