Myelin sheath

Occurrence

Myelin is a fatty substance that surrounds many nerve cells.
Since it is wrapped in a spiral around the nerve cells, the structure that is created is called a myelin sheath, also called myelin sheath.

Myelin sheaths occur in the central nervous system, i.e. in the brain, and in the peripheral nervous system, i.e. on all other nerves in the human body.

They surround the nerve cells that require rapid transmission of signals. These are, for example, the nerve cells that are responsible for executing movements.

Also in the brain and in the Spinal cord Fast forwarding is necessary, which is why there are myelin sheaths here.

Here the totality of the medullary sheaths is also called white matter designated.

function

The myelin sheaths that surround the nerve cells are for electrical insulation necessary.

The medullary sheath isolates the nerve cell to prevent new electrical impulses from constantly forming along the nerve cell in order to be able to transmit the signals. This saves time and enables one faster forwarding.

construction

A nerve cell (Neuron) consists of three parts.
Dem central cell body (Soma), the Dendritesthat receive and transmit signals from other nerve cells on one side of the cell body and the Axon with its terminal branches where the signals are passed on to the next cells.

The axon of the various nerve cells is very long depending on their location in the body.
The nerve cells that supply the legs, for example, are up to one meter in length.
It must be ensured here that the signals are passed along the axon very quickly, so that, for example, a movement initiated by the brain is not carried out seconds later, but immediately.

For this reason, the axons have a myelin sheath that surrounds them: the so-called myelin sheath.

In the central nervous system, i.e. in the brain and spinal cord, the myelin sheaths are made of so-called Oligodendrocytes educated.
This is just the special name of the cells that spiral around the nerve cells. These cells are in the peripheral nervous system Schwann cells called. But there they have the same function.

Since axons can be very long, it is not enough for a single cell to wrap around this axon to isolate them. Many of these cells wrap around the axon all along the axon.
Small gaps are created between the places where the axon is exposed. These spots are about 1 micrometer long.

They are known as Ranvier lace ringsbecause the medullary sheath looks like it is tied up here. An electrical impulse (an action potential) triggered.

Due to the insulation, this can then be passed on through the medullary sheath 1 to 1.5mm until a new impulse is triggered on the next ring. This phenomenon continues to the end of the axon. Here the impulse is then passed on to the next cell.

Diseases

The most common and well-known disease of the myelin sheath is multiple sclerosis.

Here the human body forms antibody against the very cells that make up the medullary sheaths, the oligodendrocytes. This will destroy them.

In multiple sclerosis, the medullary sheaths of the central nervous system are affected, i.e. those of the brain and spinal cord. Frequently occurs Poor eyesight as the first symptom, as the myelin sheaths, which transmit the visual information, are typically affected first.

In the further course you can Sensory disturbances and Muscle weakness added, since the correct forwarding of both incoming and forwarded signals is disturbed. The disease progresses in relapses and requires treatment by a doctor.