Characteristics of a neuron and its types. What are neurons? Motor neurons: description, structure and functions. Reflex arc: definition and brief description

The structure of a neuron.

The neuron body, which is connected to the processes, is the central part of the neuron and provides nutrition to the rest of the cell. The body is covered by a layered membrane, which consists of two layers of lipids with opposite orientations, forming a matrix in which proteins are enclosed. The neuron body has a nucleus or nuclei containing genetic material. The nucleus regulates protein synthesis throughout the cell and controls the differentiation of young nerve cells. The cytoplasm of the neuron body contains a large number of ribosomes Some ribosomes are located freely in the cytoplasm one at a time or form clusters. Other ribosomes attach to the endoplasmic reticulum, which represents internal system membranes, tubules, vesicles. Ribosomes attached to membranes synthesize proteins, which are then transported out of the cell. Clusters of smooth endoplasmic reticulum, in which ribosomes are not embedded, constitute the Golgi reticular apparatus; it is assumed to be important for the secretion of neurotransmitters and neuromodulators. Lysosomes are membrane-enclosed accumulations of various hydrolytic enzymes. Important organelles of nerve cells are mitochondria - the main energy-producing structures. The inner membrane of the mitochondrion contains all the enzymes of the cycle. citric acid- the most important link in the aerobic pathway for the breakdown of glucose, which is tens of times more effective than the anaerobic pathway. Nerve cells also contain microtubules, neurofilaments, and microfilaments that vary in diameter. Microtubules (diameter 300 nm) extend from the body nerve cell into the axon and dendrites and represent an intracellular transport system. Neurofilaments (diameter 100 nm) are found only in nerve cells, especially in large axons, and also form part of it transport system. Microfilaments (diameter 50 nm) are well expressed in the growing processes of nerve cells; they are involved in some types of interneuron connections. Dendrites are tree-like branching processes of a neuron, its main receptive field, ensuring the collection of information that comes through synapses from other neurons or directly from the environment. With distance from the body, dendritic branching occurs: the number of dendritic branches increases, and their diameter narrows.

On the surface of the dendrites of many neurons ( pyramidal neurons cortex, Purkinje cells of the cerebellum, etc.) there are spines. The spinous apparatus is integral part dendritic tubule systems: dendrites contain microtubules, neurofilaments, Golgi reticulum and ribosomes. Functional maturation and onset active work nerve cells coincides with the appearance of spines; a prolonged cessation of information flow to the neuron leads to the resorption of spines. The presence of spines increases the receptive surface of dendrites. An axon is a single, usually long, output process of a neuron that serves to quickly conduct excitation. In the end, it can branch into a large (up to 1000) number of branches. Nerve cells perform a number of general functions , aimed at maintaining own processes organizations. This is an exchange of substances with environment, formation and expenditure of energy, protein synthesis, etc. In addition, nerve cells perform specific functions unique to them in the perception, processing and storage of information. Neurons are able to perceive information, process (encode) it, quickly transmit information along specific pathways, organize interaction with other nerve cells, store information and generate it. To perform these functions, neurons have a polar organization with separation of inputs and outputs and contain a number of structural and functional parts.

Structural classification.

Based on the number and arrangement of dendrites and axons, neurons are divided into axonless neurons, unipolar neurons, pseudounipolar neurons, bipolar neurons, and multipolar (many dendritic arbors, usually efferent) neurons.

Axonless neurons- small cells, grouped nearby spinal cord in intervertebral ganglia that do not have anatomical signs of division of processes into dendrites and axons. All processes of the cell are very similar. The functional purpose of axonless neurons is poorly understood.

Unipolar neurons- neurons with one process, present, for example, in the sensory nucleus trigeminal nerve in the midbrain.

Bipolar neurons- neurons having one axon and one dendrite, located in specialized sensory organs - the retina, olfactory epithelium and bulb, auditory and vestibular ganglia.

Multipolar neurons- neurons with one axon and several dendrites. This type nerve cells predominate in the central nervous system.

The human body is a rather complex and balanced system that functions in accordance with clear rules. Moreover, outwardly it seems that everything is quite simple, but in fact our body is an amazing interaction of every cell and organ. This entire “orchestra” is conducted by the nervous system, consisting of neurons. Today we will tell you what neurons are and how important a role they play in the human body. After all, they are the ones responsible for our mental and physical health.

Every schoolchild knows that we are controlled by the brain and nervous system. These two blocks of our body are represented by cells, each of which is called nerve neuron. These cells are responsible for receiving and transmitting impulses from neuron to neuron and other cells of human organs.

To better understand what neurons are, they can be represented as the most important element nervous system, which performs not only a conducting role, but also a functional one. Surprisingly, neuroscientists still continue to study neurons and their work in transmitting information. Of course, they have achieved great success in their scientific research and managed to uncover many secrets of our body, but they still cannot once and for all answer the question of what neurons are.

Nerve cells: features

Neurons are cells and are in many ways similar to their other “brethren” that make up our body. But they have a number of features. Due to their structure, such cells in the human body, when connected, create a nerve center.

A neuron has a nucleus and is surrounded by a protective membrane. This makes it similar to all other cells, but that’s where the similarity ends. Other characteristics of a nerve cell make it truly unique:

Neurons don't divide

Neurons of the brain (brain and spinal cord) do not divide. This is surprising, but they stop developing almost immediately after their appearance. Scientists believe that a certain precursor cell completes division even before full development neuron. In the future, it increases only connections, but not its quantity in the body. Many diseases of the brain and central nervous system are associated with this fact. With age, some neurons die off, and the remaining cells, due to the low activity of the person himself, cannot build up connections and replace their “brothers”. All this leads to imbalance in the body and, in some cases, to death.

Nerve cells transmit information

Neurons can transmit and receive information using processes - dendrites and axons. They are able to perceive certain data using chemical reactions and convert it into an electrical impulse, which, in turn, passes through synapses (connections) to the necessary cells of the body.

Scientists have proven the uniqueness of nerve cells, but in fact they now know about neurons only 20% of what they actually hide. The potential of neurons has not yet been revealed; in the scientific world there is an opinion that the revelation of one secret of the functioning of nerve cells becomes the beginning of another secret. And this process in currently seems endless.

How many neurons are there in the body?

This information is not known for certain, but neurophysiologists suggest that there are more than one hundred billion nerve cells in the human body. Moreover, one cell has the ability to form up to ten thousand synapses, allowing it to quickly and effectively communicate with other cells and neurons.

Structure of neurons

Each nerve cell consists of three parts:

neuron body (soma);
dendrites;
axons.

It is still unknown which of the processes develop first in the cell body, but the distribution of responsibilities between them is quite obvious. The axon process of a neuron is usually formed in a single copy, but there can be a lot of dendrites. Their number sometimes reaches several hundred; the more dendrites a nerve cell has, the more cells it can be connected to. In addition, an extensive network of processes allows you to transmit a lot of information in the shortest possible time.

Scientists believe that before the formation of processes, the neuron spreads throughout the body, and from the moment they appear, it is already in one place without changing.

Transmission of information by nerve cells

To understand how important neurons are, it is necessary to understand how they perform their function of transmitting information. Neuron impulses are able to move in chemical and electrical form. The dendrite extension of a neuron receives information as a stimulus and transmits it to the body of the neuron; the axon transmits it as an electronic impulse to other cells. The dendrites of another neuron receive the electronic impulse immediately or with the help of neurotransmitters (chemical messengers). Neurotransmitters are captured by neurons and are subsequently used as their own.

Types of neurons by number of processes

Scientists, observing the work of nerve cells, have developed several types of their classification. One of them divides neurons by the number of processes:

unipolar;
pseudounipolar;
bipolar;
multipolar;
axonless.

A multipolar neuron is considered classic; it has one short axon and a network of dendrites. The most poorly studied are axonless nerve cells; scientists only know their location - the spinal cord.

Reflex arc: definition and brief description

In neurophysics there is such a term as “reflex arc neurons”. Without it it's quite difficult to get full view about the work and significance of nerve cells. Stimuli that affect the nervous system are called reflexes. This is the main activity of our central nervous system, it is carried out with the help of a reflex arc. It can be thought of as a kind of road along which an impulse passes from a neuron to the implementation of an action (reflex).

This path can be divided into several stages:

perception of irritation by dendrites;
transmission of impulse to the cell body;
transformation of information into an electrical impulse;
transmission of impulse to the organ;
change in organ activity (physical response to a stimulus).

Reflex arcs can be different and consist of several neurons. For example, a simple reflex arc is formed from two nerve cells. One of them receives information, and the other forces human organs to perform certain actions. Usually such actions are called an unconditioned reflex. It occurs when a person is hit, for example, kneecap, and in case of touching a hot surface.

Basically, a simple reflex arc conducts impulses through the processes of the spinal cord; a complex reflex arc conducts an impulse directly to the brain, which, in turn, processes it and can store it. Subsequently, when receiving a similar impulse, the brain sends the right command to authorities to perform a certain set of actions.

Classification of neurons by functionality

Neurons can be classified according to their direct purpose, because each group of nerve cells is intended for specific actions. The types of neurons are presented as follows:

Sensitive

These nerve cells are designed to perceive irritation and transform it into an impulse that is redirected to the brain.

They perceive information and transmit impulses to the muscles that move parts of the body and human organs.

3. Insert

These neurons carry out difficult work, they are in the center of the chain between sensory and motor nerve cells. Such neurons receive information, conduct pre-treatment and transmit a command impulse.

4. Secretory

Secretory nerve cells synthesize neurohormones and have a special structure with a large number of membrane sacs.

Motor neurons: characteristics

Efferent neurons (motor) have a structure identical to other nerve cells. Their network of dendrites is the most branched, and axons extend to muscle fibers. They cause the muscle to contract and straighten. The longest axon in the human body is the motor neuron axon, which goes to thumb legs from lumbar region. On average, its length is about one meter.

Almost all efferent neurons are located in the spinal cord, because it is responsible for most of our unconscious movements. This applies not only to unconditioned reflexes (for example, blinking), but also to any actions that we do not think about. When we peer at some object, impulses are sent to optic nerve brain. But the movement eyeball left and right are carried out through commands from the spinal cord, these are unconscious movements. Therefore, as we age and the accumulation of unconscious habitual actions increases, the importance of motor neurons appears in a new light.

Types of motor neurons

In turn, efferent cells have a certain classification. They are divided into the following two types:

a-motoneurons;
y-motoneurons.

The first type of neurons has a denser fiber structure and attaches to various muscle fibers. One such neuron can involve a different number of muscles.

Y-motoneurons are slightly weaker than their “brothers”; they cannot use several muscle fibers at the same time and are responsible for muscle tension. We can say that both types of neurons are the controlling organ of motor activity.

What muscles do motor neurons connect to?

Neuron axons are connected to several types of muscles (they are working muscles), which are classified as:

animal;
vegetative.

The first group of muscles is represented by skeletal muscles, and the second belongs to the category of smooth muscles. The methods of attachment to muscle fiber. Skeletal muscles At the point of contact with neurons, they form peculiar plaques. Autonomic neurons communicate with smooth muscles through small swellings or bubbles.

Conclusion

It is impossible to imagine how our body would function in the absence of nerve cells. They perform incredibly difficult work every second, responsible for our emotional condition, taste preferences And physical activity. Neurons have not yet revealed many of their secrets. After all, even the simplest theory about the non-restoration of neurons raises many disputes and questions among some scientists. They are ready to prove that in some cases nerve cells are capable of not only forming new connections, but also self-reproducing. Of course, this is just a theory for now, but it may well turn out to be viable.

Work on the functioning of the central nervous system is extremely important. Indeed, thanks to discoveries in this area, pharmacists will be able to develop new drugs to activate brain activity, and psychiatrists will better understand the nature of many diseases that now seem incurable.

The structural unit of the nervous system is the nerve cell, or neuron. Neurons differ from other cells in the body in many ways. First of all, their population, numbering from 10 to 30 billion (and perhaps more*) cells, is almost completely “complete” by the time of birth, and not a single neuron, if it dies, is replaced by a new one. It is generally accepted that after a person passes the period of maturity, about 10 thousand neurons die every day, and after 40 years this daily figure doubles.

* The assumption that the nervous system consists of 30 billion neurons was made by Powell and his colleagues (Powell et al., 1980), who showed that in mammals, regardless of species, there are about 146 thousand nerve cells per 1 mm 2 of nervous tissue. The total surface area of the human brain is 22 dm 2 (Changeux, 1983, p. 72).

Another feature of neurons is that, unlike other types of cells, they do not produce, secrete or structure anything; their only function is to conduct neural information.

Neuron structure

There are many types of neurons, the structure of which varies depending on the functions they perform in the nervous system; sensory neuron differs in structure from motor neuron or a neuron of the cerebral cortex (Fig. A.28).

Rice. A.28. Different types of neurons.

But whatever the function of a neuron, all neurons are made up of three main parts: the cell body, dendrites and axon.

Body neuron, Like any other cell, it consists of cytoplasm and nucleus. The cytoplasm of a neuron, however, is especially rich mitochondria, responsible for producing the energy necessary to maintain high cell activity. As already noted, clusters of neuron bodies form nerve centers in the form of a ganglion, in which the number of cell bodies is in the thousands, a nucleus, where there are even more of them, or, finally, a cortex consisting of billions of neurons. The cell bodies of neurons form the so-called Gray matter.

Dendrites serve as a kind of antenna for the neuron. Some neurons have many hundreds of dendrites that receive information from receptors or other neurons and conduct it to the cell body and its only other type of process. - axon.

Axon is the part of a neuron responsible for transmitting information to the dendrites of other neurons, muscles or glands. In some neurons, the axon length reaches a meter, in others the axon is very short. As a rule, the axon branches, forming the so-called terminal tree; at the end of each branch there is synoptic plaque. It is she who forms the connection (synapse) of a given neuron with the dendrites or cell bodies of other neurons.

Most nerve fibers (axons) are covered with a sheath consisting of myelin- a white fat-like substance that acts as an insulating material. The myelin sheath is interrupted by constrictions at regular intervals of 1-2 mm - interceptions of Ranvier, which increase the speed of a nerve impulse traveling along a fiber, allowing it to “jump” from one interception to another, rather than gradually spreading along the fiber. Hundreds and thousands of axons collected in bundles form nerve pathways, which, thanks to myelin, have the appearance white matter.

Nerve impulse

Information enters the nerve centers, is processed there and then transmitted to effectors in the form nerve impulses, running along neurons and the nerve pathways connecting them.

Regardless of what information is transmitted by nerve impulses running along billions of nerve fibers, they are no different from each other. Why, then, do impulses coming from the ear convey information about sounds, and impulses from the eye convey information about the shape or color of an object, and not about sounds or something completely different? Yes, simply because the qualitative differences between nerve signals are determined not by these signals themselves, but by the place where they arrive: if it is a muscle, it will contract or stretch; if it is a gland, it will secrete, reduce or stop secretion; if this is a certain area of the brain, a visual image of an external stimulus will be formed in it, or the signal will be deciphered in the form of, for example, sounds. Theoretically, it would be enough to change the course of nerve pathways, for example, part of the optic nerve to the area of the brain responsible for deciphering sound signals, to force the body to “hear with the eyes.”

Resting potential and action potential

Nerve impulses are transmitted along dendrites and axons not by the external stimulus itself or even its energy. An external stimulus only activates the corresponding receptors, and this activation is converted into energy electric potential, which is created at the tips of dendrites that form contacts with the receptor.

The nerve impulse that arises can be roughly compared to fire running along a fuse and igniting a dynamite cartridge located in its path; The "fire" thus spreads towards ultimate goal due to small explosions following each other. The transmission of a nerve impulse, however, is fundamentally different from this in that almost immediately after the passage of the discharge, the potential of the nerve fiber is restored.

A nerve fiber at rest can be likened to a small battery; on the outside of its membrane there is a positive charge, and on the inside there is a negative charge (Fig. A.29), and this resting potential is converted into electric current only when both poles are closed. This is exactly what happens during the passage of a nerve impulse, when the fiber membrane for a moment becomes permeable and depolarized. Following this depolarization the period is coming refractoriness, during which the membrane repolarizes and restores the ability to conduct a new impulse*. So, due to successive depolarizations, this propagation occurs action potential(i.e., nerve impulse) at a constant speed, varying from 0.5 to 120 meters per second, depending on the type of fiber, its thickness and the presence or absence of a myelin sheath.

* During the refractory period, which lasts about a thousandth of a second, nerve impulses cannot travel along the fiber. Therefore, in one second, a nerve fiber is capable of conducting no more than 1000 impulses.

Rice. A.29. Action potential. The development of the action potential, accompanied by a change in electrical voltage (from -70 to + 40 mV), is due to the restoration of equilibrium between positive and negative ions on both sides of the membrane, the permeability of which is reduced a short time increases.

The law "everything" or nothing". Because everyone nerve fiber a certain electric potential is inherent; impulses propagating along it, regardless of the intensity or any other properties of the external stimulus, always have the same characteristics. This means that an impulse in a neuron can only occur if its activation, caused by stimulation of a receptor or an impulse from another neuron, exceeds a certain threshold below which activation is ineffective; but, if the threshold is reached, a “full” impulse immediately arises. This fact is called the “all or nothing” law.

Synaptic transmission

Synapse. A synapse is the area of connection between the axon terminal of one neuron and the dendrites or body of another. Each neuron can form up to 800-1000 synapses with other nerve cells, and the density of these contacts in the gray matter of the brain is more than 600 million per 1 mm 3 (Fig. A.30)*.

*This means that if you count 1000 synapses in one second, then it will take from 3 to 30 thousand years to completely recount them (Changeux, 1983, p. 75).

Rice. A.30. Synaptic connection of neurons (in the middle - the synapse area at higher magnification). The terminal plaque of the presynaptic neuron contains vesicles with a supply of neurotransmitter and mitochondria that supply the energy necessary for transmission of the nerve signal.

The place where a nerve impulse passes from one neuron to another is, in fact, not a point of contact, but rather a narrow gap called synoptic gap. We are talking about a gap with a width of 20 to 50 nanometers (millionths of a millimeter), which is limited on one side by the membrane of the presynaptic plaque of the neuron transmitting the impulse, and on the other by the postsynaptic membrane of the dendrite or body of another neuron, which receives the nerve signal and then transmits it further.

Neurotransmitters. It is at synapses that processes occur as a result of which chemicals released by the presynaptic membrane transmit a nerve signal from one neuron to another. These substances, called neurotransmitters(or simply mediators), a kind of “brain hormones” (neurohormones), accumulate in the vesicles of synaptic plaques and are released when a nerve impulse arrives here along the axon.

After this, the mediators diffuse into the synaptic cleft and attach to specific receptor sites postsynaptic membrane, i.e. to such areas to which they “fit like a key to a lock.” As a result, the permeability of the postsynaptic membrane changes, and thus the signal is transmitted from one neuron to another; Mediators can also block the transmission of nerve signals at the synapse level, reducing the excitability of the postsynaptic neuron.

Having fulfilled their function, the mediators are broken down or neutralized by enzymes or absorbed back into the presynaptic ending, which leads to the restoration of their supply in the vesicles by the time the next impulse arrives (Fig. A.31).

Rice. A.31. la. Mediator A, whose molecules are released from the terminal plaque of neuron I, binds to specific receptors on the dendrites of neuron II. X molecules, which in their configuration do not fit these receptors, cannot occupy them and therefore do not cause any synaptic effects.

1b. M molecules (for example, the molecules of some psychotropic drugs) are similar in configuration to molecules of the neurotransmitter A and therefore can bind to receptors for this neurotransmitter, thus preventing it from performing its functions. For example, LSD interferes with serotonin's ability to suppress sensory signals.

2a and 2b. Certain substances, called neuromodulators, can act at the axon terminal to facilitate or inhibit neurotransmitter release.

The excitatory or inhibitory function of a synapse depends mainly on the type of transmitter it secretes and on the effect of the latter on the postsynaptic membrane. Some mediators always have only an excitatory effect, others only have an inhibitory effect, and others play the role of activators in some parts of the nervous system and inhibitors in others.

Main functions neurotransmitters. Currently, several dozen of these neurohormones are known, but their functions have not yet been sufficiently studied. This applies, for example, to acetylcholine, who participates in muscle contraction, causes a slowdown in heart and respiratory rates and is inactivated by an enzyme acetylcholinesterase*. The functions of such substances from the group are not fully understood monoamines, as norepinephrine, which is responsible for the wakefulness of the cerebral cortex and increased heart rate, dopamine, present in the "pleasure centers" of the limbic system and some nuclei of the reticular formation, where it participates in the processes of selective attention, or serotonin, which regulates sleep and determines the amount of information circulating in the sensory pathways. Partial inactivation of monoamines occurs as a result of their oxidation by the enzyme monoamine oxidase. This process, which usually returns brain activity to normal level, in some cases can lead to an excessive decrease in it, which psychologically manifests itself in a person in a feeling of depression (depression).

* Apparently, a lack of acetylcholine in some nuclei of the diencephalon is one of the main causes of Alzheimer's disease, and a lack of dopamine in the putamen (one of the basal ganglia) may be the cause of Parkison's disease.

Gamma-aminobutyric acid (GABA) is a neurotransmitter that performs approximately the same physiological function as monoamine oxidase. Its action consists mainly of reducing the excitability of brain neurons in relation to nerve impulses.

Along with neurotransmitters, there is a group of so-called neuromodulators, which are mainly involved in the regulation of the nervous response, interacting with neurotransmitters and modifying their effects. As an example we can name substance P And bradykinin, involved in the transmission of pain signals. The release of these substances at spinal cord synapses, however, can be suppressed by secretion endorphins And enkephalin, which thus leads to a decrease in the flow of pain nerve impulses(Fig. A.31, 2a). The functions of modulators are also performed by substances such as factorS, apparently playing an important role in sleep processes, cholecystokinin, responsible for the feeling of satiety, angiotensin, thirst regulating, and other agents.

Neurotransmitters and the effect of psychotropic substances. It is now known that various psychotropic drugs act at the level of synapses and those processes in which neurotransmitters and neuromodulators participate.

The molecules of these drugs are similar in structure to the molecules of certain mediators, which allows them to “deceive” various mechanisms of synaptic transmission. Thus, they disrupt the action of true neurotransmitters, either taking their place at the receptor sites, or preventing them from being absorbed back into the presynaptic endings or being destroyed by specific enzymes (Fig. A.31, 26).

It has been established, for example, that LSD, by occupying serotonin receptor sites, prevents serotonin from inhibiting the influx of sensory signals. In this way, LSD opens the mind to a wide variety of stimuli that continually assault the senses.

Cocaine enhances the effects of dopamine, taking its place in receptor sites. They act in a similar way morphine and other opiates, the immediate effect of which is explained by the fact that they quickly manage to occupy receptor sites for endorphins*.

* Accidents associated with drug overdose are explained by the fact that the binding of excessive amounts of, for example, heroin by zndorphin receptors in the nerve centers of the medulla oblongata leads to a sharp depression of breathing, and sometimes to a complete stop (Besson, 1988, Science et Vie, Hors serie, n° 162).

Action amphetamines due to the fact that they suppress the reuptake of norepinephrine by presynaptic endings. As a result, the accumulation of excess amounts of neurohormone in the synaptic cleft leads to an excessive degree of wakefulness in the cerebral cortex.

It is generally accepted that the effects of the so-called tranquilizers(for example, Valium) are explained mainly by their facilitating effect on the action of GABA in the limbic system, which leads to increased inhibitory effects of this neurotransmitter. On the contrary, how antidepressants These are mainly enzymes that inactivate GABA, or drugs such as, for example, monoamine oxidase inhibitors, the introduction of which increases the amount of monoamines in synapses.

Death by some poisonous gases occurs due to suffocation. This effect of these gases is due to the fact that their molecules block the secretion of an enzyme that destroys acetylcholine. Meanwhile, acetylcholine causes muscle contraction and a slowdown in heart and respiratory rates. Therefore, its accumulation in synaptic spaces leads to inhibition and then complete blockade of cardiac and respiratory functions and a simultaneous increase in the tone of all muscles.

The study of neurotransmitters is just beginning, and we can expect that hundreds, and perhaps thousands of these substances will soon be discovered, the diverse functions of which determine their primary role in the regulation of behavior.

The human body is complex system, in which many individual blocks and components take part. Externally, the structure of the body seems elementary and even primitive. However, if you look deeper and try to identify the patterns by which interaction occurs between different organs, then the nervous system will come to the fore. The neuron, which is the main functional unit of this structure, acts as a transmitter of chemical and electrical impulses. Despite the external similarity with other cells, it performs more complex and responsible tasks, the support of which is important for human psychophysical activity. To understand the features of this receptor, it is worth understanding its structure, operating principles and tasks.

What are neurons?

A neuron is a specialized cell that is capable of receiving and processing information in the process of interaction with other structural and functional units of the nervous system. The number of these receptors in the brain is 10 11 (one hundred billion). Moreover, one neuron can contain more than 10 thousand synapses - sensitive endings, through which they occur. Taking into account the fact that these elements can be considered as blocks capable of storing information, we can conclude that they contain huge amounts of information. A neuron is also a structural unit of the nervous system that ensures the functioning of the sense organs. That is, this cell should be considered as a multifunctional element designed to solve various problems.

Features of a neuron cell

Types of neurons

The main classification involves the division of neurons according to structural characteristics. In particular, scientists distinguish axonless, pseudounipolar, unipolar, multipolar and bipolar neurons. It must be said that some of these species have not yet been studied enough. This refers to axonless cells that cluster in areas of the spinal cord. There is also controversy regarding unipolar neurons. There are opinions that such cells are not present in the human body at all. If we talk about which neurons predominate in the body of higher beings, then multipolar receptors will come to the fore. These are cells with a network of dendrites and one axon. We can say that this is a classic neuron, the most commonly found in the nervous system.

Conclusion

Neuronal cells are an integral part human body. It is thanks to these receptors that the daily functioning of hundreds and thousands of chemical transmitters in the human body is ensured. On modern stage Developmental science provides an answer to the question of what neurons are, but at the same time leaves room for future discoveries. For example, today there is different opinions regarding some of the nuances of the work, growth and development of cells of this type. But in any case, the study of neurons is one of the most important tasks of neurophysiology. Suffice it to say that new discoveries in this area can shed light on more effective ways treatment of many mental illness. In addition, a deep understanding of the principles of neuron operation will make it possible to develop means that stimulate mental activity and improving memory in the new generation.

Last updated: 10/10/2013

Popular scientific article about nerve cells: structure, similarities and differences between neurons and other cells, the principle of transmission of electrical and chemical impulses.

Neuron is a nerve cell that is the main building block for the nervous system. Neurons are similar to other cells in many ways, but there is one important difference between a neuron and other cells: neurons are specialized in transmitting information throughout the body.

These highly specialized cells are capable of transmitting information both chemically and electrically. There are also several various types neurons that perform various functions V human body.

Sensory neurons carry information from sensory receptor cells to the brain. Motor (motor) neurons transmit commands from the brain to the muscles. Interneurons (interneurons) are capable of communicating information between different neurons in the body.

Neurons compared to other cells in our body

Similarities with other cells:

Neurons, like other cells, have a nucleus containing genetic information
Neurons and other cells are surrounded by a membrane that protects the cell.
The cell bodies of neurons and other cells contain organelles that support cell life: mitochondria, Golgi apparatus, and cytoplasm.

Differences that make neurons unique

Unlike other cells, neurons stop reproducing shortly after birth. Therefore, some parts of the brain have large quantity neurons at birth than later, because neurons die, but do not move. Despite the fact that neurons do not reproduce, scientists have proven that new connections between neurons appear throughout life.

Neurons have a membrane that is designed to send information to other cells. - These are special devices that transmit and receive information. Intercellular connections are called synapses. Neurons release chemical compounds(neurotransmitters or neurotransmitters) into synapses to communicate with other neurons.

Neuron structure

A neuron has only three main parts: the axon, cell body and dendrites. However, all neurons vary slightly in shape, size, and characteristics depending on the neuron's role and function. Some neurons have only a few dendritic branches, while others are highly branched in order to receive a large amount of information. Some neurons have short axons, while others may have quite long axons. The longest axon in the human body runs from the bottom of the spine to the big toe, measuring approximately 0.91 meters (3 feet) in length!

More about the structure of a neuron

Action potential

How do neurons send and receive information? For neurons to communicate, they need to transmit information both within the neuron itself and from one neuron to the next neuron. This process uses both electrical signals and chemical transmitters.

Dendrites receive information from sensory receptors or other neurons. This information is then sent to the cell body and to the axon. Once this information leaves the axon, it travels along the entire length of the axon using an electrical signal called an action potential.

Communication between synapses

As soon as the electrical impulse reaches the axon, information must be sent to the dendrites of the adjacent neuron through the synaptic cleft. In some cases, the electrical signal can cross the cleft between neurons almost instantly and continue its movement.

In other cases, neurotransmitters need to transmit information from one neuron to the next. Neurotransmitters are chemical messengers that are released from axons to cross the synaptic cleft and reach the receptors of other neurons. In a process called “reuptake,” neurotransmitters attach to a receptor and are absorbed into the neuron for reuse.

Neurotransmitters

It is an integral part of our daily functioning. It is not yet known exactly how many neurotransmitters there are, but scientists have already found more than a hundred of these chemical transmitters.

What effect does each neurotransmitter have on the body? What happens when illness or medical supplies encounter these chemical messengers? Let's list some of the main neurotransmitters, their known effects and diseases associated with them.