Neurite

Neurite is the term used to describe the cell extension of a nerve cell through which electrical impulses are transmitted to its environment. If the neurite is also surrounded by “glial cells” that isolate it, it is called an axon.

Function and structure

A neurite is the extension of a nerve cell, and directs its action potentials into the environment. It can be thought of as the connecting cable between two computers, where the computers are the nerve cells. In order to accelerate the transmission between the nerve cells, the electrical impulses it conducts “jump” at certain intervals.

It is true that for faster transmission it is often already isolated by a layer of fat (the so-called myelin sheath, which is formed by the Schwann cells). But this alone is not enough to achieve the fast impulse conduction speed of up to 400 km/h (!). At a distance of 0.2 – 1.5 mm there are also so-called “Ranvier rings” on the neurite, which interrupt the myelin sheath.

The electrical signal literally “jumps” between these rings, resulting in a strong increase in speed. A neuron usually has only one neurite as an extension, neurons with two neurites are called bipolar neurons. The neurite usually ends at another nerve cell, more precisely at a synapse.

There, the electrical signal it conducts is converted into a chemical signal and can be amplified or inhibited on its way to the next cell. A neurite that is surrounded by a myelin sheath is also called an axon. These can be up to half a meter long, as is the case in the spinal cord, but can also be only a few millimeters long.

Multiple Sclerosis

A well-known disease that has its origin in the nervous system is multiple sclerosis. The neurite is normally isolated through a myelin sheath for better isolation and faster signal transmission. In multiple sclerosis, this fat layer is destroyed by chronic inflammatory processes for reasons still unknown.

Hence the name “demyelinating disease”. Over time, nerve impulses can be transmitted more and more poorly and slowly, which leads to the typical symptoms of MS. The decline of the myelin sheath is also radiologically visible and is part of the diagnosis. MS is currently not curable, although it is easily treatable for decades.