Nerve impulse, its transformation and transmission mechanism

The human nervous system acts as a kind of coordinator in our body. It transmits commands from the brain to the musculature, organs, tissues and processes signals coming from them. As a kind of data carrier, a nerve impulse is used. What is he like? How fast does it work? On these, as well as on a number of other issues, one can find the answer in this article.

What is a nerve impulse?

This is the name of the excitation wave that propagates through the fibers as a response to neuronal stimulation. Thanks to this mechanism, information is transmitted from various receptors to the central nervous system. And from it, in turn, to different organs (muscles and glands). And what does this process mean at the physiological level? The mechanism of nerve impulse transmission is that the membranes of neurons can change their electrochemical potential. And the process that interests us is accomplished in the field of synapses. The velocity of the nerve impulse can vary within the range of 3 to 12 meters per second. More details about it, as well as the factors that affect it, we'll talk more.

Study of structure and work

For the first time the passage of a nerve impulse was demonstrated by German scientists E. Goering and H. Helmholtz on the example of a frog. At the same time, it was established that the bioelectric signal propagates with the speed indicated above. In general, this is possible due to the special construction of nerve fibers. In some ways they resemble an electrical cable. So, if you draw parallels with it, the conductors are the axons, and the insulators are their myelin sheaths (they are a membrane of the Schwann cell that is wound in several layers). And the speed of the nerve impulse depends primarily on the diameter of the fibers. The second in importance is the quality of electrical insulation. By the way, lipoprotein myelin is used as a material by the body, which possesses dielectric properties. Other things being equal, the larger the layer, the faster the nerve impulses will pass. Even at the moment it can not be said that this system has been fully investigated. Much that relates to nerves and impulses remains a mystery and subject of study.

Features of the structure and functioning

If we talk about the path of the nerve impulse, it should be noted that the myelin sheath does not cover the fiber over its entire length. The features of the construction are such that the situation is best compared with the creation of insulating ceramic couplings, which are tightly threaded onto the rod of the electrical cable (although in this case the axon). As a result, there are small non-isolated electrical sections from which the ion current can safely flow from the axon into the environment (or vice versa). This irritates the membrane. As a result, the action potential is generated in areas that are not isolated. This process is called Ranvier interception. The presence of such a mechanism makes it possible to make the nerve impulse spread much faster. Let's talk about this with examples. Thus, the speed of the nerve impulse in a thick myelinated fiber, whose diameter fluctuates within 10-20 microns, is 70-120 meters per second. While those who have a non-optimal structure, this figure is less than 60 times!

Where are they created?

Nerve impulses arise in neurons. The possibility of creating such "messages" is one of their main properties. The nerve impulse ensures rapid propagation of the same type of signals along axons for a long distance. Therefore, this is the most important means of the body for the exchange of information in it. Data on irritation are transmitted by changing the frequency of their occurrence. Here there is a complex system of periodicals that can count hundreds of nerve impulses in one second. By a somewhat similar principle, although considerably more complicated, computer electronics works. So, when nerve impulses arise in neurons, they are coded in a certain way, and only then are already transmitted. Thus the information is grouped in special "packs", which have different number and character of following. All this, combined together, is the basis for the rhythmic electrical activity of our brain, which can be registered thanks to an electroencephalogram.

Types of cells

Speaking about the sequence of the passage of the nerve impulse, we can not ignore the nerve cells (neurons), through which the transmission of electrical signals occurs. So, thanks to them, different parts of our body exchange information. Depending on their structure and functional, three types are distinguished:

1. Receptor (sensitive). They are encoded and transformed into nerve impulses of all temperature, chemical, sound, mechanical and light stimuli.
2. Insert (also called conductor or closing). They serve to process and switch impulses. The largest number is in the human brain and spinal cord.
3. Effectoral (motor). They receive commands from the central nervous system to ensure that certain actions are performed (in the bright sun, close your eyes and so on).

Each neuron has a cell body and an outgrowth. The path of the nerve impulse along the body begins precisely with the latter. The processes are of two types:

1. Dendrites. They have the function of perceiving the irritation of the receptors located on them.
2. Axons. Thanks to them, nerve impulses are transmitted from cells to the working organ.

Interesting aspect of activity

Speaking about carrying out of a nervous impulse by cages, it is difficult to not tell about one interesting moment. So, when they are at rest, then, let's say, the sodium-potassium pump moves the ions in such a way as to achieve the effect of fresh water inside and salty outwardly. Due to the resulting imbalance of the potential difference, up to 70 millivolts can be observed on the membrane. For comparison, this is 5% of the usual AA batteries. But as soon as the state of the cell changes, the resulting equilibrium is broken, and the ions begin to change places. This happens when the path of a nerve impulse passes through it. Due to the active action of ions, this action is also called the action potential. When it reaches a certain index, then the reverse processes begin, and the cell reaches a state of rest.

On the action potential

Speaking about the transformation of the nerve impulse and its spread, it should be noted that it could amount to a miserable millimeter per second. Then the signals would pass from the hand to the brain in minutes, which is clearly not good. Here, and played a role in strengthening the potential of the action, the previously examined shell of myelin. And all of its "gaps" are placed in such a way that they only have a positive effect on the speed of signal transmission. So, when the end of the main part of one axon body is reached by the impulse, it is transmitted either to the next cell, or (if to speak of the brain) to the numerous branches of the neurons. In the latter cases, a slightly different principle works.

How does it work in the brain?

Let's talk, which transfer sequence of the nerve impulse works in the most important parts of our CNS. Here neurons from their neighbors are separated by small slits, which are called synapses. The potency of action can not pass through them, so it seeks a different way to get to the next nerve cell. At the end of each process there are small sacs, which are called presynaptic vesicles. In each of them there are special compounds - neurotransmitters. When the action potential comes to them, then the molecules are released from the sacs. They cross the synapse and join the special molecular receptors that are located on the membrane. At the same time, the equilibrium is disturbed and, probably, a new action potential appears. It is not certain yet, neurophysiologists are engaged in studying the issue to this day.

Neurotransmitter work

When they transmit nerve impulses, then there are several options that will happen to them:

1. They will diffuse.
2. Undergo chemical cleavage.
3. Go back to their bubbles (this is called reverse capture).

At the end of the 20th century, a striking discovery was made. Scientists have learned that drugs that affect neurotransmitters (as well as their ejection and re-acquisition) can change a person's mental state in a fundamental way. So, for example, a number of antidepressants like "Prozac" block the reverse capture of serotonin. There are some reasons to believe that Parkinson's disease is responsible for the deficiency in the brain of the neurotransmitter dopamine.

Now researchers who study the borderline states of the human psyche are trying to figure out how this all affects the human mind. In the meantime, we do not have an answer to such a fundamental question: what makes a neuron create the potential for action? While the mechanism of "launching" this cell for us is a secret. Particularly interesting from the point of view of this puzzle is the work of the neurons of the brain.

In short, they can work with thousands of neurotransmitters that are sent by their neighbors. Details on the processing and integration of this type of impulse are almost unknown to us. Although this is working on a lot of research groups. At the moment it turned out that all the impulses received are integrated, and the neuron decides whether it is necessary to maintain the action potential and transfer them further. On this fundamental process, the functioning of the human brain is based. Well, then it's no wonder that we do not know the answer to this riddle.

Some theoretical features

The article "nervous impulse" and "action potential" were used as synonyms. Theoretically, this is true, although in some cases it is necessary to take into account some features. So, if we go into details, then the action potential is only a part of the nerve impulse. With a detailed examination of scholarly books, one can learn that this is only called a change in the membrane charge from positive to negative, and vice versa. Whereas a nervous impulse is understood as a complex structural-electrochemical process. It propagates through the neuron's membrane as a traveling wave of changes. The action potential is just an electrical component in the nerve impulse. It characterizes the changes that occur with the charge of the local portion of the membrane.

Where are the nerve impulses created?

Where do they start their journey? The answer to this question can be given by any student who diligently studied the physiology of excitement. There are four options:

1. Receptor end of dendrite. If it is (which is not a fact), then it is possible to have an adequate stimulus, which will first create a generator potential, and then a nerve impulse. Pain receptors work in a similar way.
2. Membrane of excitatory synapse. As a rule, this is possible only if there is strong irritation or their summation.
3. Trigger zone of dentrida. In this case, local excitatory postsynaptic potentials are formed as a response to the stimulus. If the first interception of Ranvier is myelinated, then they are summed up on it. Due to the presence of a membrane site, which has an increased sensitivity, a nerve impulse appears here.
4. Axon mound. This is the place where the axon begins. A hillock is the most frequent to create impulses on a neuron. In all other places that were considered earlier, their occurrence is much less likely. This is due to the fact that here the membrane has an increased sensitivity, as well as a lower critical level of depolarization. Therefore, when the summation of numerous excitatory postsynaptic potentials begins, the mound reacts first of all to them.

Example of propagating excitation

Story medical terms can cause misunderstanding of certain moments. To eliminate this, it is worthwhile to briefly go over the above knowledge. As an example, let's take a fire.

Remember the summaries of last summer's news (also it will soon be heard again). The fire is spreading! In this case, trees and shrubs that burn, remain in their places. But the front of the fire goes farther from the place where the fire was. The nervous system works in a similar way.

Often it is necessary to calm the onset of excitation of the nervous system. But this is not so easy to do, as in the case of fire. To do this, they perform artificial interference in the work of a neuron (for therapeutic purposes) or use various physiological means. This can be compared to flooding a fire with water.