Functions of the neuron. What function is performed by neurons. Function of the motor neuron

The ability of cells to respond to stimuli of the external world is the main criterion of a living organism. Structural elements of the nervous tissue - mammalian and human neurons - are able to transform stimuli (light, smell, sound waves) into the excitation process. Its final result is an adequate reaction of the organism in response to various environmental influences. In this article we will study what function the neurons of the brain and the peripheral parts of the nervous system perform, and also consider the classification of neurons in connection with the features of their functioning in living organisms.

Nerve tissue formation

Before studying the functions of a neuron, let's look at how neuronal cells are formed. At the neurula stage, a neural tube is laid in the embryo. It is formed from an ectodermal leaf that has a thickening - a neural plate. The extended end of the tube will subsequently form five parts in the form of cerebral bubbles. From them the brain regions are formed . The main part of the neural tube in the process of embryonic development forms the spinal cord, from which 31 pairs of nerves leave.

Neurons of the brain combine to form nuclei. Of these, 12 pairs of cranial nerves come out. In the human body, the nervous system is differentiated into the central part - the brain and spinal cord, which consists of neurocells, and the supporting tissue - neuroglia. The peripheral department consists of a somatic and a vegetative part. Their nerve endings innervate all the organs and tissues of the body.

Neurons are structural units of the nervous system

They have different sizes, shapes and properties. Functions of the neuron are diverse: participation in the formation of reflex arcs, perception of stimulation from the external environment, transfer of the arising excitation to other cells. From the neuron departs a few processes. The long one is an axon, short branches and are called dendrites.

Cytological studies revealed in the body of the nerve cell a nucleus with one or two nucleoli, a well-formed endoplasmic reticulum, many mitochondria and a powerful protein-synthesizing apparatus. It is represented by ribosomes and molecules of RNA and mRNA. These substances form a specific structure of neurocytes - the substance of Nissl. A feature of nerve cells - a large number of processes contributes to the fact that the main function of the neuron is the transmission of nerve impulses. It is provided by both dendrites and axon. The first perceive the signals and transmit them to the body of the neurocyte, and the axon is the only very long process, conducts excitation to other nerve cells. Continuing to find the answer to the question: what function do the neurons do to the structure of such a substance as neuroglia.

Nerve tissue structures

Neurocytes are surrounded by a special substance, which has basic and protective properties. For him also a characteristic ability to divide. This compound is called neuroglia.

This structure is closely related to nerve cells. Since the main functions of the neuron are the generation and conduction of nerve impulses, the glial cells are under the influence of the excitation process and change their electrical characteristics. In addition to trophic and protective functions, glia provides metabolic reactions in neurocytes and promotes the plasticity of the nervous tissue.

The mechanism of excitation in neurons

Each nerve cell forms several thousand contacts with other neurocytes. Electrical impulses, which are the basis of excitation processes, are transmitted from the body of the neuron along the axon, and it contacts other structural elements of the nervous tissue or enters directly into the working organ, for example, into the muscle. To establish what function neurons perform, it is necessary to study the mechanism of transmission of excitation. It is carried out by axons. In motor nerves they are covered with a myelin sheath and are called pulpy. In the autonomic nervous system there are demyelinous processes. According to them, the stimulation should go to the neighboring neurocyte.

What is a synapse?

The place of contact of two cells is called a synapse. Transmission of excitation in it occurs either with the help of chemical substances - mediators, or by passing ions from one neuron to another, that is, electrical impulses.

Due to the formation of synapses, neurons create a reticular structure of the trunk portion of the brain and parts of the spinal cord. It is called the reticular formation, it starts from the lower part of the medulla oblongata and captures the nuclei of the brain stem, or neurons of the brain. The mesh structure supports the active state of the cerebral cortex and directs the reflex acts of the spinal cord.

Artificial Intelligence

The idea of synaptic connections between the neurons of the central nervous system and the study of the functions of the reticular information is currently embodied in science as an artificial neural network. In it, the outputs of one artificial nerve cell are connected to the entrances by another special connections duplicating their functions with real synapses. The activation function of the neuron of an artificial neurocomputer is the summation of all input signals entering the artificial nerve cell, transformed into a nonlinear function from the linear component. It is also known as the actuation function (transfer function). When creating artificial intelligence, linear, semilinear and step activation functions of the neuron were most widely used.

Afferent neurocytes

They are also called sensitive and have short processes that enter the skin cells and all internal organs (receptors). Perceiving the stimulation of the external environment, the receptors transform them into the process of excitation. Depending on the type of stimulus, the nerve endings are divided into: thermoreceptors, mechanoreceptors, nociceptors. Thus, the functions of a sensitive neuron are the perception of stimuli, their discrimination, the generation of excitation and its transfer to the central nervous system. Sensory neurons enter the posterior horns of the spinal cord. Their bodies are located in the nodes (ganglia) located outside the central nervous system. Thus, the ganglions of the brain and spinal nerves are formed. Afferent neurons have a large number of dendrites, together with the axon and the body they are an obligatory component of all reflex arcs. Therefore, the functions of a sensitive neuron are both in the transmission of the excitation process to the brain and spinal cord, and in the participation in the formation of reflexes.

Features of interneuron

Continuing to study the properties of the structural elements of the nervous tissue, we will find out what function the intercalary neurons perform. This kind of nerve cells takes bioelectric impulses from the sensory neurocyte and transmits them:

A) other interneurons;

B) motor neurocytes.

Most interneurons have axons, terminal sections of which are terminus, are associated with the neurocytes of one center.

The insertion neuron, whose functions - the integration of excitation and its spreading further into the central nervous system, are an obligatory component of most unconditioned reflex and conditioned reflex nerve arches. Excitatory interneurons contribute to signal transmission between the functional groups of the neurocytes. Braking interstitial nerve cells are excited from their own center by feedback. This contributes to the fact that the intercalary neuron, whose functions - transmission and long-term preservation of nerve impulses, provides activation of sensory spinal nerves.

Function of the motor neuron

Motoneuron is the final structural unit of the reflex arc. He has a large body enclosed in the anterior horn of the spinal cord. Those nerve cells that innervate skeletal muscles have the names of these motor elements. Other efferent neurocytes enter the gland secreting cells and cause secretion of the corresponding substances: secretions, hormones. In the involuntary, that is, unconditioned reflex acts (swallowing, salivation, defecation) efferent neurons depart from the spinal cord or from the brain stem part. To perform complex actions and movements, the body uses two types of centrifugal neurocytosis: the central motor and peripheral motor cells. The body of the central motoneuron is located in the cerebral cortex, near the Roland furrow.

The bodies of peripheral motor neurocytes innervating the muscles of the limbs, trunk, and neck are located in the anterior horns of the spinal cord, and their long processes - the axons - come out from the front roots. They form motor fibers of 31 pairs of spinal nerves. Peripheral motor neurocytes innervating the muscles of the face, pharynx, larynx, and tongue are located in the nuclei of the wandering, sublingual and glossopharyngeal cranial nerves. Therefore, the main function of the motor neuron is the unimpeded excitation of muscles, secreting cells and other working organs.

Metabolism in Neurocytes

The main functions of the neuron - the formation of the bioelectric potential of the action and its transfer to other nerve cells, muscles, secreting cells - are due to the peculiarities of the structure of the neurocyte, as well as to specific metabolic reactions. Cytological studies have shown that neurons contain a large number of mitochondria, synthesizing ATP molecules, a developed granular reticulum with a variety of ribosomal particles. They actively synthesize cellular proteins. The membrane of the nerve cell and its processes, the axon and dendrites, serves as a selective transport of molecules and ions. Metabolic reactions in neurocytes occur with the participation of a variety of enzymes and are characterized by high intensity.

Transmission of excitation in synapses

Considering the mechanism of conduction of excitation in neurons, we got acquainted with synapses - formations arising at the site of contact of two neurocytes. Excitation in the first nerve cell causes the formation in the collaterals of its axon molecules of chemical substances - mediators. These include amino acids, acetylcholine, noradrenaline. Standing out of the bubbles of the synoptic endings in the synoptic gap, it can affect both its own postsynaptic membrane and affect the envelopes of neighboring neurons.

Molecules of neurotransmitters serve as an irritant for another nerve cell, causing changes in charge in its membrane - the action potential. Thus, the excitation rapidly spreads through the nerve fibers and reaches the central nervous system or enters the muscles and glands, causing them to act adequately.

Plasticity of neurons

Scientists found that in the process of embryogenesis, namely in the stage of neurulation, a very large number of primary neurons develop from the ectoderm. About 65% of them die before birth. During ontogenesis, some cells of the brain continue to be eliminated. This is a natural programmed process. Neurocytes, unlike epithelial or connective cells, are incapable of dividing and regenerating, since the genes responsible for these processes are inactivated in human chromosomes. Nevertheless, the brain and mental performance may persist for many years, not significantly decreasing. This is due to the fact that the functions of the neuron lost in the process of ontogenesis are assumed by other nerve cells. They have to increase their metabolism and create new additional neural connections that compensate for lost functions. This phenomenon is called the plasticity of the neurocytes.

What is reflected in neurons

At the end of the twentieth century, a group of Italian neurophysiologists found an interesting fact: in the nerve cells a mirror reflection of consciousness is possible. This means that the phantom of the consciousness of people with whom we communicate is formed in the cerebral cortex. The neurons entering the mirror system act as resonators of the mental activity of the surrounding people. Therefore, a person is able to foresee the intentions of the interlocutor. The structure of such neurocytes also provides a special psychological phenomenon, called empathy. It is characterized by the ability to penetrate into the world of the other person's emotions and empathize with his feelings.