Myelin: what is the purpose, how to restore the myelin sheath

The nervous system performs essential functions in the body. She is responsible for all actions and thoughts of a person, forms his personality. But all this complex work would be impossible without one component - myelin.

Myelin is a substance that forms the myelin (pulp) membrane, which is responsible for the electrical insulation of nerve fibers and the speed of transmission of electrical impulses.

Myelin anatomy in the structure of the nerve

The main cell of the nervous system is a neuron. The body of the neuron is called the soma. There is a core inside it. The body of the neuron is surrounded by short processes called dendrites. They are responsible for communication with other neurons. One long process, the axon, departs from the soma. It carries an impulse from a neuron to other cells. Most often, at the end, it connects with the dendrites of other nerve cells.

The entire surface of the axon is covered by the myelin sheath, which is a process of the Schwann cell, devoid of cytoplasm. Essentially, these are several layers of the cell membrane wrapped around an axon.

The Schwann cells enveloping the axon are separated by Ranvier interceptions, which lack myelin.

Functions

The main functions of the myelin sheath are:

• isolation of the axon;
• acceleration of impulse conduction;
• energy savings due to the conservation of ion flows;
• support of the nerve fiber;
• axon nutrition.

How impulses work

Nerve cells are isolated due to their membranes, but they are nevertheless interconnected. The areas where the cells touch are called synapses. This is where the axon of one cell meets the soma or dendrite of another.

An electrical impulse can be transmitted within a single cell or from neuron to neuron. This is a complex electrochemical process, which is based on the movement of ions through the membrane of the nerve cell.

In a calm state, only potassium ions enter the neuron, while sodium ions remain outside. At the moment of arousal, they begin to change places. The axon is positively charged from within. Then sodium ceases to flow through the membrane, and the outflow of potassium does not stop.

The change in voltage due to the movement of potassium and sodium ions is called the "action potential". It spreads slowly, but the myelin sheath surrounding the axon accelerates this process, preventing the outflow and influx of potassium and sodium ions from the axon body.

Passing through the interception of Ranvier, the impulse jumps from one section of the axon to another, which allows him to move faster.

After the action potential crosses the gap in myelin, the impulse stops and the resting state returns.

This method of energy transfer is characteristic of the central nervous system. As far as the autonomic nervous system is concerned, there are often axons covered with little or no myelin. There are no jumps between the Schwann cells, and the impulse passes much more slowly.

Composition

The myelin layer consists of two layers of lipids and three layers of protein. It contains much more lipids (70-75%):

• phospholipids (up to 50%);
• cholesterol (25%);
• glactocerebroside (20%), etc.

The high fat content makes the myelin sheath white, due to which the neurons covered with it are called "white matter".

Protein layers are thinner than lipid layers. Protein content in myelin - 25-30%:

• proteolipid (35-50%);
• myelin basic protein (30%);
• Wolfram proteins (20%).

There are simple and complex proteins in the nervous tissue.

The role of lipids in the structure of the membrane

Lipids play a key role in the structure of the pulp. They are the structural material of nerve tissue and protect the axon from energy loss and ion currents. Lipid molecules have the ability to repair brain tissue after damage. Myelin lipids are responsible for the adaptation of the mature nervous system. They act as hormone receptors and communicate between cells.

The role of proteins

Protein molecules are of great importance in the structure of the myelin layer. They, along with lipids, act as a building material for nerve tissue. Their main task is to transport nutrients to the axon. They also decode the signals entering the nerve cell and speed up the reactions in it. Participation in metabolism is an important function of myelin sheath protein molecules.

Myelination defects

The destruction of the myelin layer of the nervous system is a very serious pathology, due to which there is a violation of the transmission of a nerve impulse. It causes dangerous diseases, often incompatible with life. There are two types of factors that influence the onset of demyelination:

• genetic predisposition to the destruction of myelin;
• the effect on myelin of internal or external factors.
• Demyelization is divided into three types:
• sharp;
• remitting;
• acute monophasic.

Why is destruction happening

The most common causes of pulp destruction are:

• rheumatic diseases;
• a significant predominance of proteins and fats in the diet;
• genetic predisposition;
• bacterial infections;
• heavy metal poisoning;
• tumors and metastases;
• prolonged severe stress;
• bad ecology;
• pathology of the immune system;
• long-term use of antipsychotics.

Diseases due to demyelination

Demyelinating diseases of the central nervous system:

1. Canavan's disease - a genetic disease that occurs at an early age. It is characterized by blindness, problems with swallowing and eating, impaired motility and development. Epilepsy, macrocephaly and muscle hypotension are also a consequence of this disease.
2. Binswanger's disease. Most often caused by arterial hypertension. Patients expect thought disorders, dementia, as well as impaired walking and pelvic organ functions.
3. Multiple sclerosis. May cause damage to several parts of the central nervous system. It is accompanied by paresis, paralysis, seizures, and motor impairment. Also, symptoms of multiple sclerosis are behavioral disorders, weakening of the facial muscles and vocal cords, and impaired sensitivity. Vision is impaired, the perception of color and brightness changes. Multiple sclerosis is also characterized by disorders of the pelvic organs and dystrophy of the brainstem, cerebellum, and cranial nerves.
4. Devik's disease - demyelination in the optic nerve and spinal cord. The disease is characterized by impaired coordination, sensitivity and functions of the pelvic organs. She is distinguished by severe visual impairment and even blindness. In the clinical picture, paresis, muscle weakness and autonomic dysfunction are also observed.
5. Osmotic demyelination syndrome. It occurs due to a lack of sodium in the cells. Symptoms are seizures, personality disorders, loss of consciousness, up to coma and death. The consequence of the disease is cerebral edema, hypothalamic infarction and hernia of the brain stem.
6. Myelopathy - various dystrophic changes in the spinal cord. They are characterized by muscle disorders, sensory disorders and pelvic dysfunction.
7. Leukoencephalopathy - destruction of the myelin sheath in the subcortex of the brain. Patients suffer from constant headache and epileptic seizures. Impaired vision, speech, coordination and walking are also observed. Sensitivity decreases, personality and consciousness disorders are observed, dementia progresses.
8. Leukodystrophy - a genetic metabolic disorder that causes the destruction of myelin. The course of the disease is accompanied by muscle and movement disorders, paralysis, impaired vision and hearing, progressive dementia.

Demyelinating diseases of the peripheral nervous system:

1. Guillain-Barré syndrome is an acute inflammatory demyelination. It is characterized by muscle and movement disorders, respiratory failure, partial or complete absence of tendon reflexes. Patients suffer from heart disease, disruption of the digestive system and pelvic organs. Paresis and sensory disturbances are also signs of this syndrome.
2. Charcot-Marie-Tooth neural amyotrophy is a hereditary pathology of the myelin sheath. It is distinguished by sensitivity disorders, dystrophy of the limbs, spinal deformity and tremor.

This is only part of the diseases that arise due to the destruction of the myelin layer. The symptoms are similar in most cases. An accurate diagnosis can only be made after a computed tomography or magnetic resonance imaging. The level of qualification of the doctor plays an important role in the diagnosis.

Principles of casing defects treatment

Diseases associated with the destruction of the pulp are very difficult to treat. Therapy is aimed mainly at relieving symptoms and stopping the destruction processes. The earlier the disease is diagnosed, the more chances to stop its course.

Myelin recovery options

Thanks to timely treatment, the myelin recovery process can be triggered. However, the new myelin sheath will not function as well. In addition, the disease can go into a chronic stage, and the symptoms will persist, only slightly soften. But even a slight remyelination can stop the course of the disease and partially restore the lost functions.

Modern drugs aimed at myelin regeneration are more effective, but they are very expensive.

Therapy

For the treatment of diseases caused by the destruction of the myelin sheath, the following drugs and procedures are used:

• beta-interferons (stop the course of the disease, reduce the risk of relapse and disability);
• immunomodulators (affect the activity of the immune system);
• muscle relaxants (help restore motor functions);

• nootropics (restore conductive activity);
• anti-inflammatory (relieve the inflammatory process that caused the destruction of myelin);
• neuroprotectors (prevent damage to brain neurons);
• pain relievers and anticonvulsants;
• vitamins and antidepressants;
• filtration of cerebrospinal fluid (a procedure aimed at cleansing cerebrospinal fluid).

Disease prognosis

Currently, the treatment of demyelination does not give one hundred percent result, but scientists are actively developing drugs aimed at restoring the pulp. Research is carried out in the following areas:

1. Stimulation of oligodendrocytes. These are the cells that make myelin. In a demyelinated organism, they do not work. Artificial stimulation of these cells will help start the process of repairing damaged areas of the myelin sheath.
2. Stem cell stimulation. Stem cells can be transformed into complete tissue. There is a possibility that they can fill the flesh as well.
3. Regeneration of the blood-brain barrier. During demyelination, this barrier breaks down and allows lymphocytes to negatively affect myelin. Its restoration protects the myelin layer from the attack of the immune system.

Perhaps, in the near future, diseases associated with the destruction of myelin will cease to be incurable.