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What are the axons of neurons?

What are the axons of neurons?

May 23, 2022

Neurons are nerve cells thanks to which we are able to think, feel, make decisions and, even more, have awareness.

However, although the concept of "neuron" is well known even beyond laboratories and university classrooms, the truth is that to understand what our mental life is like, it is not enough to know that in our heads there are tiny cells that They send nerve impulses to each other. You also have to understand that there are different parts of neurons, responsible for different tasks . Axons are one of these components .

What is an axon?

A neuronal axon is a kind of sleeve or "arm" that leaves from the center of the neuron and goes to a place away from this . The shape of this small structure gives us clues about its function. Basically, the role of the axons is to make the electrical signals that travel through the neurons go to another place in the body.

The axon is, therefore, a kind of conduit through which nervous impulses pass at full speed ; It acts as a communication channel between the central part of the neuron (which is called neuronal soma or body of the neuron and where the nucleus is with DNA) and another part of the nervous system that this electrical stimulus has to reach.

At the end of the axons there is either a part of nerve fiber that contracts when the electrical signal is delivered to it, or there is a synaptic space between neurons, which is the point at which these nerve cells communicate with each other, usually through of chemical signals. That is to say, that at the tip of the axons, the electric impulse usually becomes a pattern of chemical particle release that they reach the other neuron through the synaptic space .

The size of axons

If the human body is characterized by something, it is because of its complexity and because of the great variety of pieces that work together to make it work well. In the case of neuronal axons, that means that the size of these depends on the type of neuron to which it belongs and its location and function. In the end, what happens in our nervous system has a decisive influence on our chances of survival, and that is why evolution has been responsible for the existence in our species of many specialized nerve cells of different shape and configuration.

The length of axons of neurons can vary greatly depending on their function. For example, neurons with axons shorter than one millimeter are often found in gray matter regions of the brain, while outside the central nervous system there are several axons that measure more than one span, despite being very thin. In short, in many cases, axons are so short that the distance between their tip and the body of the neuron is microscopic, and in other cases they can be several centimeters long to be able to reach remote areas without intermediaries.

As for the thickness of axons in humans, they are usually between one and 20 micrometers (thousandths of a millimeter) in diameter. However, this is not a universal rule that applies to all animals with nerve cells. For example, in some invertebrate species, such as squid, the axons can reach a millimeter thick , which can be easily seen with the naked eye. This is so because the thicker the axon is, the faster the electric impulse travels, and in the case of squid this is an important ability to make the siphon through which water is ejected work well, since they must contract a large part of muscle tissue at the same time to be able to escape quickly by jet propulsion.

The formation of the nerves

As we have seen, axons are not found only in the brain. Like what happens with neuronal soma, They are spread throughout the body : by internal organs, arms and legs, etc.

In fact, a nerve is, mainly, a set of axons which is so thick that we can see it directly without the need for a microscope. When we find a nerve in a portion of meat, what we are seeing is nothing more and nothing less than many axons grouped in a bundle, combined with other auxiliary nerve cells.

The myelin sheaths

Many times the axons are not alone, but rather they are accompanied by elements known as myelin sheaths , which adhere to its surface to the point of appearing to be an inseparable component of the neuron.

Myelin is a fatty substance that acts on axons in a similar way to a rubber insulator along an electrical cord, but not exactly.In short, the myelin sheaths, which are distributed along the axon creating a shape similar to a string of sausages, separate the inside of the axons from the outside of these, so the electrical signal is not lost through from the walls and travel much faster. The protection offered is directed both to the neuron itself and to the electrical signal that is transmitted through it.

In fact, thanks to the myelin sheaths the electricity is not progressing continuously along the axon, but it is jumping between the points of this in which there is a separation between the myelin sheaths, some areas called Ranvier nodules . To understand it better, for the purposes of the agility with which electricity travels, this supposes the same difference between going up a ramp and going up stairs, appearing each time two steps higher. Something similar to what might be expected happens if the electrical impulse were teleported to travel small axon stretches, from one node of Ranvier to the next.

2-Minute Neuroscience: The Neuron (May 2022).

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