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Interneurons. Sensory or sensory neuron In what substance of the brain is the interneuron located?

A neuron is a specific, electrically excitable cell in the human nervous system and has unique characteristics. Its functions are to process, store and transmit information. Neurons are characterized by a complex structure and narrow specialization. They are also divided into three types. This article describes in detail the interneuron and its role in the action of the central nervous system.

Classification of neurons

The human brain has approximately 65 billion neurons that constantly communicate with each other. These cells are divided into several types, each of which performs its own special functions.

The sensory neuron plays the role of a transmitter of information between the sense organs and the central parts of the human nervous system. It perceives a variety of irritations, which it converts into nerve impulses, and then transmits the signal to the human brain.

Motor - sends impulses to various organs and tissues. This type is mainly involved in the control of spinal cord reflexes.

The interneuron is responsible for processing and switching impulses. The functions of this type of cell are to receive and process information from the sensory and motor neurons between which they are located. Moreover, interneurons (or intermediate neurons) occupy 90% of the human central nervous system, and are also found in large quantities in all areas of the brain and spinal cord.

The structure of intermediate neurons

An interneuron consists of a body, an axon and dendrites. Each part has its own specific functions and is responsible for a specific action. Its body contains all the components from which cellular structures are created. The important role of this part of the neuron is to generate nerve impulses and perform trophic function. The elongated process that carries the signal from the cell body is called an axon. It is divided into two types: myelinated and non-myelinated. At the end of the axon there are various synapses. The third component of neurons is dendrites. They are short processes that branch in different directions. Their function is to deliver impulses to the neuron body, which ensures communication between different types of neurons in the central nervous system.

Sphere of influence

What determines the area of influence of an interneuron? First of all, his own structure. Basically, cells of this type have axons whose synapses end on neurons of the same center, which ensures their unification. Some interneurons are activated by others, from other centers, and then deliver information to their neural center. Such actions enhance the impact of the signal, which is repeated in parallel paths, thereby extending the storage period of information data in the center. As a result, the location where the signal was delivered increases the reliability of the influence on the executive structure. Other interneurons can receive activation from connections of motor “brothers” from their center. Then they become transmitters of information back to their center, thereby creating feedback connections. Thus, the interneuron plays an important role in the formation of special closed networks that extend the storage period of information in the nerve center.

Excitatory type of interneurons

Interneurons are divided into two types: excitatory and inhibitory. When the former are activated, the transfer of data from one neural group to another is facilitated. This task is performed by “slow” neurons, which have the ability to activate for a long time. They transmit signals for quite a long time. In parallel with these actions, intermediate neurons activate their “fast” “colleagues”. When the activity of “slow” neurons increases, the reaction time of “fast” ones decreases. At the same time, the latter somewhat slow down the work of the “slow” ones.

Inhibitory type of interneurons

An inhibitory interneuron comes into an active state due to direct signals that enter or emanate from their center. This action occurs through feedback. Direct excitation of this type of interneurons is characteristic of the intermediate centers of the sensory pathways of the spinal cord. And in the motor centers of the cerebral cortex, interneurons are activated due to feedback.

The role of interneurons in the functioning of the spinal cord

In the functioning of the human spinal cord, an important role is played by the conduction pathways, which are located outside the bundles that perform the conduction function. It is along these paths that the impulses sent by the intercalary and sensory neurons move. Signals travel up and down these pathways, conveying various information to the corresponding parts of the brain. The interneurons of the spinal cord are located in the intermedial nucleus, which, in turn, is located in the dorsal horn. Interneurons are an important anterior part of the spinocerebellar tract. On the back of the spinal cord horn are fibers consisting of interneurons. They form the lateral spinothalamic tract, which performs a special function. It is a conductor, that is, it transmits signals about pain and temperature sensitivity first to the diencephalon, and then to the cerebral cortex itself.

More information about interneurons

In the human nervous system, interneurons perform a special and extremely important function. They connect different groups of nerve cells and transmit signals from the brain to the spinal cord. Although this type is the smallest in size. The shape of the interneurons resembles a star. The bulk of these elements are located in the gray matter of the brain, and their processes do not protrude beyond the human central nervous system.

Interneurons (also interneurons, conductor or intermediate, interneuron) are a type that are usually located in integral parts, whose (output elements) and (processes) are limited to one area of the brain.

This feature distinguishes them from others, which often have axonal projections outside the brain region where their cell bodies and dendrites are located.

While the main networks of neurons are entrusted with the functions of processing and storing information, as well as the formation of the main sources of information output from any region of the brain, conductor neurons, by definition, have local axons that control activity.

Sensory and motor neurons use glutamate as a neurotransmitter, while conductor neurons often use gamma-aminobutyric acid () for inhibition.

Interneurons work by hyperpolarizing large groups of principal cells. Spinal cord interneurons may use glycine or GABA and glycine to inhibit principal cells, while interneurons of the cortical regions or basal ganglia may release various peptides (cholecystokinin, somatostatin, vasoactive intestinal polypeptide, enkephalins, neupopeptide Y, galanin, etc.) and GABA .

Their diversity, both in structure and functionality, increases with the complexity of local networks in a given brain region, which is likely correlated with the complexity of the functions performed by the brain region. Accordingly, the six-layer (neocerebral cortex), as the center of higher mental functions such as conscious perception or cognition, has the largest number of types of interneurons.

Video about the principle of structure and operation of interneuron (in English):

The role of interneurons in the functioning of the spinal cord

The integration of sensory feedback signals and central motor commands at multiple levels of the central nervous system plays a critical role in motor control.

Studies of the cat spinal cord have shown that receptor afferents and descending motor pathways at this level converge on common spinal interneurons.

Human studies have documented how the integration of motor commands and receptor response signals are used to control muscle activity during movement. During locomotion, a collection of convergent inputs from a central order generator (a neural network that supplies rhythmically ordered motor signals without feedback), sensory feedback, descending commands, and other intrinsic properties caused by various neurotransmitters, results in the activity of conductor neurons.

Neurotransmitters

Sensory information transmitted to the spinal cord is modulated by a complex network of excitatory and inhibitory interneurons. Different neurotransmitters are released from different interneurons, but the two most common neurotransmitters are GABA, the primary inhibitory neurotransmitter, and glutamate, the primary excitatory neurotransmitter. – , which activates interneurons by binding to a receptor on the membrane.

Inhibitory interneuron

Joints are controlled by two opposing sets of muscles called extensors and flexors, which must work in unison to produce the correct, specified movement. When the neuromuscular spindle is stretched and the stretch reflex is activated, the opposing muscles must be blocked to prevent the agonist muscle from working. The spinal interneuron is responsible for its inhibition. Thus, during intentional movement, inhibitory interneurons are used to coordinate muscle contraction.

Afferent innervation of antagonist muscles is not possible without the work of interneurons

In general, depending on the tasks and responsibilities assigned to neurons, they are divided into three categories:

- Sensory neurons receive and transmit impulses from receptors “to the center”, i.e. central nervous system. Moreover, the receptors themselves are specially trained cells of the sensory organs, muscles, skin and joints that can detect physical or chemical changes inside and outside our body, convert them into impulses and joyfully transmit them to sensory neurons. Thus, signals travel from the periphery to the center.

Next type:

- Motor (motor) neurons, which rumbling, fircha and beeping, carry signals coming from the brain or spinal cord to the executive organs, which are muscles, glands, etc. Yeah, that means the signals go from the center to the periphery.

Well intermediate (intercalary) neurons, simply put, they are “extension cords”, i.e. receive signals from sensory neurons and send these impulses further to other intermediate neurons, or directly to motor neurons.

In general, this is what happens: in sensory neurons, dendrites are connected to receptors, and axons are connected to other neurons (interneurons). In motor neurons, on the contrary, dendrites are connected to other neurons (interneurons), and axons are connected to some effector, i.e. a stimulator of muscle contraction or gland secretion. Well, accordingly, interneurons have both dendrites and axons connected to other neurons.

It turns out that the simplest path along which a nerve impulse can travel will consist of three neurons: one sensory, one intercalary and one motor.

Yeah, let’s now remember the guy - a very “nervous pathologist”, with a malicious smile, knocking his “magic” hammer on his knee. Sound familiar? Now, this is the simplest reflex: when it hits the knee tendon, the muscle attached to it stretches and the signal from the sensory cells (receptors) located in it is transmitted along sensory neurons to the spinal cord. And already in it, sensory neurons contact either through intercalary or directly with motor neurons, which in response send impulses back to the same muscle, causing it to contract and the leg to straighten.

The spinal cord itself is conveniently nestled inside our spine. It is soft and vulnerable, which is why it hides in the vertebrae. The spinal cord is only 40-45 centimeters in length, as thick as a little finger (about 8 mm) and weighs some 30 grams! But, despite all its frailty, the spinal cord is the control center of a complex network of nerves spread throughout the body. Almost like a mission control center! :) Without it, neither the musculoskeletal system nor the main vital organs can function and work.

The spinal cord originates at the level of the edge of the occipital foramen of the skull and ends at the level of the first and second lumbar vertebrae. But below the spinal cord in the spinal canal there is such a dense bundle of nerve roots, funny called the cauda equina, apparently for its resemblance to it. So, the cauda equina is a continuation of the nerves coming out of the spinal cord. They are responsible for the innervation of the lower extremities and pelvic organs, i.e. transmit signals from the spinal cord to them.

The spinal cord is surrounded by three membranes: soft, arachnoid and hard. And the space between the soft and arachnoid membranes is also filled with a large amount of cerebrospinal fluid. Through the intervertebral foramina, spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 or 2 coccygeal. Why steam? Yes, because the spinal nerve exits through two roots: posterior (sensitive) and anterior (motor), connected into one trunk. So, each such pair controls a certain part of the body. That is, for example, if you accidentally grabbed a hot pan (God forbid! Pah-pah-pah!), then a pain signal immediately arises in the endings of the sensory nerve, immediately entering the spinal cord, and from there - into paired motor nerve, which transmits the order: “Akhtung-akhtung! Remove your hand immediately!” Moreover, believe me, this happens very quickly - even before the brain registers the pain impulse. As a result, you manage to pull your hand away from the pan before you feel pain. Of course, this reaction saves us from severe burns or other damage.

In general, almost all of our automatic and reflex actions are controlled by the spinal cord, well, with the exception of those that are monitored by the brain itself. Well, for example: we perceive what we see with the help of the optic nerve going to the brain, and at the same time we turn our gaze in different directions with the help of the eye muscles, which are controlled by the spinal cord. Yes, and we cry the same on the orders of the spinal cord, which “manages” the lacrimal glands.

We can say that our conscious actions come from the brain, but as soon as we begin to perform these actions automatically and reflexively, they are transferred to the spinal cord. So, when we are just learning to do something, then, of course, we consciously think about and think through and comprehend every movement, which means we use the brain, but over time we can already do it automatically, and this means that the brain transfers the “reins of power” of this action to the spinal one, it’s just that he has already become bored and uninteresting... because our brain is very inquisitive, inquisitive and loves to learn!

Well, it’s time for us to get curious......

In the gray matter of the anterior horns each segment of the spinal cord there are several thousand neurons that are 50-100% larger than most other neurons. They are called anterior motor neurons. The axons of these motor neurons exit the spinal cord through the ventral roots and directly innervate skeletal muscle fibers. There are two types of these neurons: alpha motor neurons and gamma motor neurons.

Alpha motor neurons. Alpha motor neurons give rise to large motor fibers of the A-alpha (Ace) type with an average diameter of 14 μm. After entering the skeletal muscle, these fibers branch repeatedly to innervate large muscle fibers. Stimulation of a single alpha fiber excites from three to several hundred skeletal muscle fibers, which, together with the motor neuron innervating them, constitute the so-called motor unit.

Gamma motor neurons. Along with alpha motor neurons, the stimulation of which leads to contraction of skeletal muscle fibers, much smaller gamma motor neurons are localized in the anterior horns of the spinal cord, the number of which is approximately 2 times less. Gamma motor neurons transmit impulses along much thinner motor fibers of the A-gamma (Ay) type with an average diameter of about 5 microns.

They innervate small special fibers skeletal muscles, called intrafusal muscle fibers. These fibers form the central part of the muscle spindles involved in the regulation of muscle tone.

Interneurons. Interneurons are present in all areas of the gray matter of the spinal cord, in the dorsal and anterior horns, and in the space between them. These cells are approximately 30 times more numerous than anterior motor neurons. Interneurons are small in size and very excitable, often exhibit spontaneous activity and are capable of generating up to 1500 impulses/sec.

They have numerous connections each other, and many also synapse directly with anterior motor neurons. Interconnections between interneurons and anterior motor neurons are responsible for most of the integrative functions of the spinal cord, as discussed later in this chapter.

Essentially the whole set of different types of nerve circuits, is found within a pool of spinal cord interneurons, including diverging, converging, rhythmically discharging, and other types of circuits. This chapter outlines the many ways in which these various circuits are involved in the spinal cord's execution of specific reflex actions.

Only few sensory signals, entering the spinal cord along the spinal nerves or descending from the brain, reach directly the anterior motor neurons. Instead, almost all signals are conducted first through interneurons, where they are processed accordingly. The corticospinal tract terminates almost entirely at the spinal interneurons, where signals from this tract combine with signals from other spinal tracts or spinal nerves before they converge on the anterior motor neurons to regulate muscle function.

The function of the nervous system is

1) management of the activities of various systems that make up the whole organism,

2) coordination of the processes occurring in it,

3) establishing relationships between the body and the external environment.

The activity of the nervous system is reflexive in nature. Reflex (lat. reflexus - reflected) is the body's response to any impact. This can be external or internal influence (from the external environment or from one’s own body).

The structural and functional unit of the nervous system is neuron(nerve cell, neurocyte). A neuron consists of two parts - body And shoots. The processes of a neuron, in turn, are of two types - dendrites And axons. The processes along which the nerve impulse is carried to the body of the nerve cell are called dendrites. The process along which the nerve impulse is directed from the body of the neuron to another nerve cell or to the working tissue is called axon. Nervenaya cellcapable of transmitting nervousimpulse in one direction onlynii - from the dendrite through the cell body toaxon.

Neurons in the nervous system form chains along which nerve impulses are transmitted (moved). The transmission of a nerve impulse from one neuron to another occurs at the places of their contacts and is ensured by a special kind of anatomical structures called interneuronal synapseowls.

In a nerve chain, different neurons perform different functions. In this regard, the following three main types of neurons are distinguished:

1. sensory (afferent) neuron.

2. interneuron.

3. effector (efferent) neuron.

Sensitive, (receptive,orafferent) neurons. Main characteristics of sensory neurons:

A) Tate sensory neurons always lie in nodes (spinal nodes), outside the brain or spinal cord;

b) a sensory neuron has two processes - one dendrite and one axon;

V) sensory neuron dendrite follows to the periphery to one or another organ and ends there with a sensitive ending - receptor. Receptor this is an organ which is capable of converting the energy of external influence (irritation) into a nerve impulse;

G) sensory neuron axon sent to the central nervous system, to the spinal cord or to the brainstem, as part of the dorsal roots of the spinal nerves or corresponding cranial nerves.

A receptor is an organ that is capable of converting the energy of external influence (irritation) into a nerve impulse. It is located at the end of the dendrite of the sensory neuron

The following are distinguished: types of recipetori depending on location:

1) Exteroceptors perceive irritation from the external environment. They are located in the outer integument of the body, in the skin and mucous membranes, in the sensory organs;

2) Interoceptors receive irritation from the internal environment of the body, they are located in the internal organs;

3) Proprioceptors perceive irritations from the musculoskeletal system (in muscles, tendons, ligaments, fascia, joint capsules.

Sensory neuron function– perception of an impulse from the receptor and its transmission to the central nervous system. I.P. Pavlov attributed this phenomenon to the beginning of the analysis process.

Insertable, (associative, closing, or conductor neuron ) carries out the transfer of excitation from the sensitive (afferent) neuron to the efferent ones. Closing (intercalary) neurons lie within the central nervous system.

Effector, (efferent)neuron. There are two types of efferent neurons. This dvigator neuron,Andsecretory neuron. Basic properties motor neurons:

(nerve cell) - the main structural and functional unit of the nervous system; a neuron generates, receives and transmits nerve impulses, thus transmitting information from one part of the body to another (see figure). Each neuron has a large cell body (or perikaryon (...

Psychological Encyclopedia

Nerve cell, the basic structural and functional unit of the nervous system. Although they come in a wide variety of shapes and sizes and are involved in a wide range of functions, all neurons consist of a cell body, or soma, containing a nucleus and nerve processes: an axon and...

In general, depending on the tasks and responsibilities assigned to neurons, they are divided into three categories:

Next type:

It turns out that the simplest path along which a nerve impulse can travel will consist of three neurons: one sensory, one intercalary and one motor.

Yeah, let’s now remember the guy - a very “nervous pathologist”, with a malicious smile, knocking his “magic” hammer on his knee. Sound familiar? Now, this is the simplest reflex: when it hits the knee tendon, the muscle attached to it stretches and the signal from the sensory cells (receptors) located in it is transmitted through sensory neurons to the spinal cord. And already in it, sensory neurons contact either through intercalary or directly with motor neurons, which in response send impulses back to the same muscle, causing it to contract and the leg to straighten.

Well, it’s time for us to get curious......

The peripheral nervous system (systerna nervosum periphericum) is a conditionally distinguished part of the nervous system, the structures of which are located outside the brain and spinal cord. The peripheral nervous system includes 12 pairs of cranial nerves extending from the spinal cord and brain to the periphery and 31 pairs of spinal nerves.
Cranial nerves include: Olfactory nerve(nervus olfactorius) - 1st pair, refers to the nerves of special sensitivity. It starts from the olfactory receptors of the nasal mucosa in the superior nasal concha. It consists of 15 - 20 thin nerve filaments formed by non-pulp fibers. The threads do not form a common trunk, but penetrate into the cranial cavity through the cribriform plate of the ethmoid bone, where they are attached to the cells of the olfactory bulb. The fibers of the olfactory pathway conduct impulses to the subcortical, or primary, centers of smell, from where some of the fibers are sent to the cerebral cortex. Oculomotor nerve(nervus oculomotorius) - 3rd pair, is a mixed nerve. Nerve fibers emerge from the brain stem onto the inner surfaces of the cerebral peduncles and form a relatively large nerve that runs forward in the outer wall of the cavernous sinus. Along the way, the nerve fibers of the sympathetic plexus of the internal carotid artery join it. The branches of the oculomotor nerve approach the levator palpebrae superioris, the superior, internal and inferior rectus muscles and the inferior oblique muscle of the eyeball.
Trochlear nerve(nervus trochlearis) - 4th pair, belongs to the motor nerves. The nucleus of the trochlear nerve is located in the midbrain. Curving around the cerebral peduncle from the lateral side, the nerve exits the base of the brain, passing between the peduncle and the temporal lobe. Then, together with the oculomotor nerve, it passes from the skull to the orbit and innervates the superior oblique muscle of the eyeball.