Introduction

The nervous system (systema nervosum) is divided into central and peripheral sections. The central nervous system (CNS) is represented by the brain (encephalon) and spinal cord (medulla spinalis). The central nervous system ensures the interconnection of all parts of the nervous system and their coordinated work.

Spinal cord

The spinal cord is located in the spinal canal and is a cylindrical cord, flattened from front to back, with an average length of 45 cm in men and 41-42 cm in women.

The spinal cord performs two important functions: reflex and conduction. The entire nervous system functions according to reflex principles. By participating in the perception of sensory information, the spinal cord regulates segmental reflex activity.

The spinal cord is protected by the bone tissue of the spine and surrounded by membranes. The thickness of the spinal cord is uneven and along its length there are 2 thickenings: cervical (intemescentia cervicalis) and lumbar (intemescentia lumbalis)

Following the lumbar enlargement, the brain disappears, forming the conus medullaris. It is located at the level of the second lumbar vertebra. And then the final thread stretches, which ends at the level of the second coccygeal vertebra. And it is attached to it. Thickening develops in parallel with the growth and formation of the limbs. Nerves extend from the cervical thickening to the arms, and from the lumbar to the legs. Thickenings are accumulations of nerve cells.

The spinal cord is much shorter than the spine, as it matures earlier and finishes growing earlier.

Rice. Structure of the spinal cord: 1 - Pia mater spinalis (soft shell); 2 - Sulcus medianus posterior (posterior median groove); 3 - Sulcus intermedius posterior (intermediate posterior groove); 4 - Radix dorsalis (posterior root); 5 - Cornu dorsale (back horn); 6 - Cornu laterale (lateral horn); 7 - Cornu ventrale (front horn); 8 - Radix ventralis (anterior root); 9 - A. spinalis anterior (anterior spinal artery); 10 - Fissura mediana anterior (anterior median fissure)

Gray and white matter of the spinal cord

The substance of the spinal cord is heterogeneous. Gray and white matter are distinguished.

Gray matter - substantia grisea

White matter - substantia alba

On a cross section of the spinal cord, the zone of gray matter surrounding the central canal is clearly visible in the form of a butterfly, or in the shape of the letter H. This zone is formed by the bodies and dendrites of neurons. Along the periphery there is white matter, consisting of axons, the fat-like myelin sheaths of which determine the characteristic color of this zone.

Gray matter of the spinal cord

Gray matter is formed by a huge number of neurons grouped into nuclei. It distinguishes between three types of multipolar neurons:

1. Root cells - large motor neurons (motoneurons) and efferent motor neurons of the autonomic nervous system. They participate in the formation of the anterior roots (Radix ventralis) of the spinal nerves. They are directed to the periphery and innervate skeletal muscles.

2. Tufted neurons - their axons form the majority of the ascending pathways going from the spinal cord to the brain (bundles of white matter), as well as their own bundles of the spinal cord, connecting different segments of the spinal cord. These are switching neurons.

3. Internal cells - their numerous processes do not extend beyond the gray matter, forming synapses in it with other neurons of the spinal cord.

Gray matter, substantia grisea, is located inside the spinal cord and is surrounded on all sides by white matter. Gray matter forms two vertical columns located in the right and left halves of the spinal cord. In the middle of it is a narrow central canal, canalis centralis, of the spinal cord, running the entire length of the latter and containing cerebrospinal fluid. The gray matter surrounding the central canal is called the intermediate, substantia intermedia centralis. Each column of gray matter has 2 columns: anterior, coliimna anterior, and posterior, coliimna posterior.

On transverse sections of the spinal cord, these columns look like horns: anterior, widened, cornu anterius, and posterior, pointed, cornu posterius. Therefore, the general appearance of gray matter against a white background resembles the letter H.

Throughout the entire spinal cord, the gray matter is divided into paired anterior and posterior columns (columna grisea anterior et posterior). In the interval from the I thoracic to the I-II lumbar vertebrae, lateral columns (columna lateralis) are added to them.

On a cross section, three horns are distinguished in the gray matter: cornu posterior, cornu lateralis and cornu anterior (anterior, lateral and posterior horns).

Hind horns

The dorsal horns contain intercalary neurons, which either form part of reflex arcs that close at the segment level, or form ascending pathways that carry sensory information to the brain. The neurons that switch and process pain signals are located closest to the surface of the dorsal horn. Somewhat more ventral are the cells, the axons of which conduct impulses from skin receptors. Deepest in the dorsal horns are interneurons that receive information from muscle receptors.

Structure of the posterior horn

Roland's jellylike substance consists of neuroglia. It contains small neurons of stellate and triangular shape. Their axons serve intrasegmental connections. Roland's substance is especially clearly expressed in the upper cervical and lumbar segments, and somewhat decreases in the thoracic segments.

The zona spongiosum is also formed by glial tissue and contains small multipolar neurons.

The marginal Lissauer zone is well defined in the lumbosacral region and mainly consists of the central processes of the spinal ganglion cells, which enter the spinal cord as part of the dorsal roots (radix dorsalis). There are also small fusiform neurons. Their dendrites branch in the spongy zone, and the axons extend into the lateral cord of the white matter and participate in the formation of their own bundles of the spinal cord.

The head of the posterior horn contains its own nucleus. Its head forms the spinothalamic tract and the anterior spinal tract. At the base of the posterior horn, in its medial part, there is Clark's column. This is a large thoracic core. Clark's column stretches from the I thoracic to the II lumbar segment of the vertebrae. From it arise fibers that form the posterior spinal tract. The lateral part of the base of the dorsal horn is occupied by neurons that participate in the formation of intra- and intersegment connections of the spinal cord.

Neurons of the spongy zone and gelatinous substance, as well as intercalary cells in other parts of the posterior columns, close reflex connections between the sensory cells of the spinal ganglia and the motor cells of the anterior horns with switching in the nucleus proper.

Side horns

The lateral horns are clearly defined only in the case of the sympathetic nervous system. The axons of the lateral horn cells exit the spinal cord as part of the anterior roots. In the sacral region, the lateral horns are no longer prominent, and the vegetative cells located there lie at the base of the anterior horn.

The lateral horns project only in the thoracolumbar spinal cord and contain sympathetic neurons. Here lie the medial and lateral intermediate nuclei.

Parasympathetic neurons are located below, reaching the V sacral segment. They also form an intermediate nucleus. Its fibers go to the pelvic internal organs.

Front horns

The ventral horns of the gray matter contain motonerones. They are not located randomly, but in accordance with the innervated muscles. Thus, contractions of the trunk muscles are triggered by motor neurons located more ventrally, and contractions of the limb muscles are triggered by motor neurons located more dorsally. The anterior horns are most developed in the cervical and sacral parts of the spinal cord, where the motor neurons innervating the limbs are located. The largest motor nerve cells belong to the group of alpha motor neurons. In addition to them, relatively small gamma motor neurons are also present in the ventral horns. Their function is not related to the control of skeletal muscle contractions (as in the case of alpha neurons), but to the work of muscle receptors.

Between the lateral and posterior horns of the white matter there are short strands of gray matter that make up the reticular formation of the spinal cord

The right and left columns of the gray matter of the spinal cord are connected by commissures (commissura grissa posterior and commissura grissa anterior), separated by the central canal of the spinal cord.

The gray matter of the spinal cord directly passes into the gray matter of the brain stem, and part of it spreads along the rhomboid fossa and the walls of the aqueduct, and part of it is divided into separate nuclei of cranial nerves or nuclei of bundles of pathways.

White matter of the spinal cord

The white matter of the spinal cord performs a conductive function and transmits nerve impulses. It includes three systems of pathways - ascending, descending and the spinal cord's own pathways.

The ascending tracts of the spinal cord transmit sensory information from the trunk and limbs (pain, skin, muscle, visceral) to the brain. Descending pathways carry control commands (somatic and autonomic) from the brain to the spinal cord. Proprietary pathways connect the neurons of the higher and lower segments of the spinal cord. This is necessary for the coordinated work of gray matter zones that control different muscles during simultaneous contraction (for example, the muscles of the arms and legs during walking and running). In addition, in the case of many large muscles, the motor neurons innervating them are stretched in the rostro-caudal direction into several segments. The connection between them is also provided by the spinal cord's own pathways.

The white matter of the spinal cord consists of nerve processes that make up three systems of nerve fibers:

1. Short bundles of associative fibers connecting parts of the spinal cord at different levels (afferent and interneurons)

2. Long centripetal (sensitive, afferent) neurons.

3. Long centrifugal (motor, efferent) neurons.

The first system (short fibers) belongs to the spinal cord proper apparatus, and the other two make up the conductive apparatus of bilateral connections with the brain.

The distribution of white fibers in the white matter is ordered. Having the same origin and initial function, nerve fibers are collected in bundles, forming cords (funiculus) - posterior, middle and anterior.

In the posterior cords there are ascending tracts, in the anterior cords there are mainly descending tracts, in the lateral cords there are both. The spinal cord's own tracts are directly adjacent to the gray matter in the region of both the posterior, anterior and lateral cords.

A cross-section of different levels of the spinal cord shows that in the upper segments there is much more white matter than gray matter; in the lower segments it is the other way around. This is explained by the fact that in the thoracic and, especially, cervical regions, the white matter contains almost all the axons connecting the spinal cord with the brain (both ascending and descending). The fibers that reach the lower sections connect only the lumbar, sacral and coccygeal segments of the spinal cord to the brain. Consequently, there are significantly fewer of them left.

The spinal cord is made of gray and white matter . Gray matter consists of nerve cell bodies and nerve fibers - processes of nerve cells. White matter formed only by nerve fibers - processes of nerve cells (spinal cord and brain). Gray matter occupies a central position in the spinal cord. The central canal runs through the center of the gray matter. Outside the gray matter is the white matter of the spinal cord.

In each half of the spinal cord, gray matter forms gray columns. The right and left gray pillars are connected by a transverse plate - a gray commissure, in the center of which the opening of the central channel is visible. Anterior to the central canal is the anterior commissure of the spinal cord, and behind is the posterior commissure. On a cross section of the spinal cord, the gray columns, together with the gray commissure, have the shape of the letter “H” or a butterfly with spread wings (Fig. 2.5). The lateral projections of gray matter are called horns. There are paired, wider anterior horns and narrow, also paired posterior horns. In the anterior horns of the spinal cord there are large nerve cells - motor neurons (motoneurons). Their axons form the bulk of the fibers of the anterior roots of the spinal nerves. The neurons located in each anterior horn form five nuclei: two medial and two lateral, as well as a central nucleus. The processes of the cells of these nuclei are directed to the skeletal muscles.

The posterior horn consists of interneurons, the processes of which (axons) are sent to the anterior horn, and also pass through the anterior white commissure to the opposite side of the spinal cord.

The nerve fibers (sensitive) of the dorsal roots, which are processes of nerve cells whose bodies are located in the spinal ganglia, end on the nerve cells of the nuclei of the dorsal horns. The peripheral part of the dorsal horns processes and conducts pain impulses. The average is associated with skin (tactile) sensitivity. The area at the base of the dorsal horn provides processing and conduction of muscle sensation.

The intermediate zone of gray matter of the spinal cord is located between the anterior and posterior horns. In this zone, from the VIII cervical to the II lumbar segment, there are projections of gray matter - the lateral horns. The lateral horns contain the centers of the sympathetic part of the autonomic nervous system in the form of groups of nerve cells united in the lateral (lateral) intermediate substance. The axons of these cells pass through the anterior horn and exit the spinal cord as part of the anterior roots of the spinal nerves. The intermedial nucleus (see Fig. 2.5) is the main “computing center” of the spinal cord. Here, sensory signals processed in the dorsal horn are compared with signals from the brain and a decision is made to initiate an autonomic or motor response. In the first case, trigger stimuli are sent to the lateral horn, in the second - to the anterior horn.

The spinal cord consists of nerve cells and fibers of gray matter, which in cross section looks like the letter H or a butterfly with spread wings. On the periphery of the gray matter is white matter, formed only by nerve fibers.

The gray matter of the spinal cord contains a central canal. It is a remnant of the neural tube cavity and contains cerebrospinal fluid. The upper end of the canal communicates with the IV ventricle, and the lower, slightly expanding, forms a blindly ending terminal ventricle. The walls of the central canal of the spinal cord are lined with ependyma, around which there is a central gelatinous (gray) substance. In an adult, the central canal becomes overgrown in various parts of the spinal cord, and sometimes throughout its entire length.

The gray matter along the spinal cord to the right and left of the central canal forms symmetrical gray columns. Anterior and posterior to the central canal of the spinal cord, these gray columns are connected to each other by thin plates of gray matter, called the anterior and posterior commissures.

In each column of gray matter, its front part is distinguished - the anterior column, and its back part - the posterior column. At the level of the lower cervical, all thoracic and two upper lumbar segments of the spinal cord, the gray matter on each side forms a lateral protrusion - the lateral column. In other parts of the spinal cord (above the VIII cervical and below the II lumbar segments) there are no lateral columns.

In a cross section of the spinal cord, the columns of gray matter on each side have the appearance of horns. There is a wider anterior horn and a narrow posterior horn, corresponding to the anterior and posterior columns. Side horn, matches

lateral intermediate column (autonomous) of gray matter.

The anterior horns contain large nerve root cells - motor (efferent) neurons. These neurons form 5 nuclei: two lateral (antero- and posterolateral), two medial (antero- and posteromedial) and a central nucleus. The posterior horns of the spinal cord are represented predominantly by smaller cells. The dorsal, or sensory, roots contain central processes of pseudounipolar cells located in the spinal (sensitive) ganglia.

The gray matter of the dorsal horns of the spinal cord is heterogeneous. The bulk of the nerve cells of the dorsal horn form its own nucleus. In the white matter immediately adjacent to the apex of the posterior horn of the gray matter, a border zone is distinguished. Anterior to the latter in the gray matter is a spongy zone, which received its name due to the presence in this section of a large-loop glial network containing nerve cells. A gelatinous substance consisting of small nerve cells is secreted even more anteriorly. The processes of nerve cells of the jellylike substance, the spongy zone and tuft cells diffusely scattered throughout the gray matter communicate with several neighboring segments. As a rule, they end in synapses with neurons located in the anterior horns of their segment, as well as the above and underlying segments. Directing from the posterior horns of the gray matter to the anterior horns, the processes of these cells are located along the periphery of the gray matter, forming a narrow border of white matter near it. These bundles of nerve fibers are called the anterior, lateral and posterior intrinsic bundles.

The cells of all nuclei of the dorsal horns of the gray matter are, as a rule, intercalary (intermediate, or conductor) neurons. Neurites extending from nerve cells, the totality of which

makes up the central and thoracic nuclei of the dorsal horns, are directed in the white matter of the spinal cord to the brain.

The intermediate zone of gray matter of the spinal cord is located between the anterior and posterior horns. Here, from the VIII cervical to the II lumbar segment, there is a protrusion of gray matter - the lateral horn.

In the medial part of the base of the lateral horn, a well-defined layer of white matter, the thoracic nucleus, consisting of large nerve cells, is noticeable. This nucleus extends along the entire posterior column of gray matter in the form of a cellular cord (Clark's nucleus). The largest diameter of this nucleus is at the level from the XI thoracic to the I lumbar segment. The lateral horns contain the centers of the sympathetic part of the autonomic nervous system in the form of several groups of small nerve cells,

united in the lateral intermediate (gray) matter. The axons of these cells pass through the anterior horn and exit the spinal cord as part of the ventral roots.

In the intermediate zone there is a central intermediate (gray) substance, the cell processes of which participate in the formation of the spinocerebellar tract. At the level of the cervical segments of the spinal cord, between the anterior and posterior horns, and at the level of the upper thoracic segments, between the lateral and posterior horns, a reticular formation is located in the white matter adjacent to the gray matter. The reticular formation here looks like thin bars of gray matter intersecting in different directions and consists of nerve cells with a large number of processes.

The gray matter of the spinal cord with the posterior and anterior roots of the spinal nerves and its own bundles of white matter bordering the gray matter forms its own, or segmental, apparatus of the spinal cord. The main thing is

the significance of the segmental apparatus as the phylogenetically oldest part of the spinal cord is the implementation of innate reactions (reflexes) in response to irritation (internal or external). I. P. Pavlov defined this type of activity of the segmental apparatus of the spinal cord with the term<безусловные рефлексы>.

1. Spinal nerves. Reflex arc.

1. Autonomic nervous system: sympathetic, parasympathetic and metasympathetic divisions.

None of the structures of the nervous system can function normally without interaction with others. Nevertheless, the entire NS can be divided into topographical - depending on the location of one or another part of it, and functional – according to the functions performed (principles).

According to topographic principle The nervous system is divided into:

Central - The central nervous system includes the brain and spinal cord, protected by the meninges.

Peripheral- The peripheral nervous system consists of nerves, ganglia, nerve plexuses and nerve endings.

More specific peripheral nervous system human includes 12 pairs of cranial nerves, 31 pairs of spinal nerves, sensory, sensory and autonomic ganglia, nerve plexuses.

The nerve plexus is a collection of nerve fibers from different nerves that innervate the skin, skeletal muscles of the body and internal organs in humans and vertebrates. In addition, the nerve plexus may include small autonomic ganglia.

Depending on their location, nerve plexuses are divided into: intra- and extra-organ. One of the largest and most famous plexuses is the celiac (solar) plexus.

At the ends of the processes of neurons there are nerve endings - the terminal apparatus of the nerve fiber. According to the functional division of neurons, they are distinguished receptor, effector And interneuronal graduation.

Receptor the endings are the terminals of the dendrites of sensory neurons that perceive irritation. Such endings exist, for example, in skin sensitivity systems.

Effector terminals are the endings of the axons of executive neurons that form synapses on muscle fibers or glandular cells.

Interneuronal the endings are the endings of the axons of intercalary and sensory neurons, forming synapses on other neurons.

Functionally the nervous system is divided into somatic And vegetative nervous system. Each of them has a central one, i.e. located in the NS, and peripheral - located outside the NS - parts. Somatic The nervous system is a section of the nervous system that regulates the functioning of skeletal muscles, triggering behavioral reactions and connecting the body with the external environment. A person can arbitrarily (at his own request) control the activity of skeletal muscles. Vegetative (autonomic) nervous system (ANS) - a section of the nervous system that regulates the functioning of internal organs. The ANS controls the activity of smooth and cardiac muscles and glands, regulating (strengthening or weakening) and coordinating the activity of internal organs. A person without special training cannot consciously control the activity of this system, i.e. it is involuntary. The ANS is divided into sympathetic, parasympathetic and metasympathetic divisions.

All body functions can be divided into:

Somatic“animals” - these functions are associated with the perception of external stimuli and motor reactions carried out by skeletal muscles.

Vegetative“plant” - the implementation of metabolism in the body (digestion, blood circulation, respiration, excretion, etc.), as well as growth and reproduction, depends on these functions.

The division of the entire NS into autonomic and somatic is to some extent arbitrary, since the IUD innervates all organs, including somatic ones (the IUD fibers approach the vessels passing through the skeletal muscles, thus taking part in maintaining muscle tone), participating in their nutrition.

As is known, in addition to morphological differences between smooth and skeletal muscles, there are also functional differences between them. The skeletal muscle of the tour responds to the influence of the environment with quick, purposeful movements that can be voluntarily adjusted. Smooth muscles embedded in internal organs and blood vessels work slowly but rhythmically; its activity usually does not lend itself to arbitrary regulation. These functional differences are associated with differences in innervation: skeletal muscles receive impulses from the somatic part of the NS, smooth muscles - from the autonomic part. The autonomic nervous system (ANS) innervates not only smooth muscles, but also other executive organs that are not amenable to voluntary regulation - the heart muscle and glands. In general, the ANS performs an adaptation-trophic function, i.e. adapts the level of activity of tissues and organs to the tasks they are performing at the current time. These tasks, in turn, are usually associated with one or another activity of the body in changing environmental conditions.

Recall that in the autonomic nervous system, the efferent part of the arc consists of two neurons: preganglionic (the last or only central neuron) and ganglionic (located in the autonomic ganglion). From this arrangement of neurons follows the main feature of the ANS - the two-neuronality of the efferent pathway. The axons of the central neurons of the ANS, which end on the cells of the autonomic ganglia, are called preganglionic fibers, and the axons of the executive neurons (which are located in the ganglia) are called postganglionic. Preganglionic fibers are covered with a myelin sheath, postganglionic fibers are characterized by its absence (the so-called gray fibers).

There are some exceptions to the rule of two-neuron effector pathways:

1. Postganglionic sympathetic fibers going to the smooth muscles of the gastrointestinal tract predominantly end not on muscle fibers, but on parasympathetic ganglion cells located in the walls of the stomach and intestines. Apparently, they reduce the activity of these cells and thus have an inhibitory effect on smooth muscle (3-neuron structure of the efferent pathway).

2. Chromaffin cells of the adrenal medulla are innervated not by post-, but by preganglionic sympathetic fibers. Chromaffin cells produce adrenaline under the influence of impulses reaching them through sympathetic fibers. These cells essentially correspond to postganglionic neurons, with which they have a common origin from the ganglion plate (1-neuron structure of the efferent pathway).

The ANS is divided into two sections - sympathetic And parasympathetic , which are usually called systems. Most organs are innervated by both sympathetic and parasympathetic fibers. However, in some cases, a predominant importance of one department is observed. The lacrimal glands and nasopharyngeal glands are innervated only by the parasympathetic nervous system. The bladder has mainly parasympathetic innervation. On the other hand, only sympathetic fibers approach the smooth muscles of blood vessels (with the exception of the vessels of the brain and arteries of the genital organs), sweat glands, spleen, and secretory cells of the adrenal glands.

Recently, another department has been distinguished in the autonomic nervous system - metasympathetic (enteric) nervous system . Its distinctive feature is reflex arcs that do not pass through the central nervous system. That is, both sensory, intercalary, and executive neurons are located outside the central nervous system, directly in the walls of the innervated organ. Thanks to this, many internal organs, after cutting the sympathetic and parasympathetic pathways or even after being removed from the body (if appropriate conditions are created), continue to perform their inherent functions without any noticeable changes. For example, the peristaltic function of the intestine is preserved, the heart, washed with saline, contracts, the lymphatic vessels contract and unclench, etc. At the same time, having quite a lot of independence, the metasympathetic nervous system maintains connection with the rest of the nervous system, since both sympathetic and parasympathetic neurons form synapses on its nerve cells.

The sympathetic and parasympathetic systems are different from each other:

Functionally(according to the activity performed). Functional differences are due to the fact that the sympathetic and parasympathetic systems, as a rule, have opposite effects on various organs and tissues. If the sympathetic department excites any part of the body, then the parasympathetic department inhibits it and vice versa. Thus, irritation of the sympathetic nerve innervating the heart enhances its work, and irritation of the parasympathetic vagus nerve inhibits heart contractions. However, one should not think that there is strict antagonism between the sympathetic and parasympathetic parts of the ANS, and that their functions are completely opposed. These are interacting parts, the relationship between them changes dynamically at different phases of the activity of a particular organ, i.e. they function in harmony. For example, both sympathetic and parasympathetic stimulation cause salivation. But in the first case, the saliva will be thick, saturated with organic substances, and in the second, it will be liquid and watery. The hypothalamus (the highest autonomic center), the reticular formation, and a number of other autonomic centers participate in the regulation of the activity of the entire ANS. The sympathetic nervous system prepares the body for active action. It increases metabolism, enhances breathing and heart function, increases the supply of oxygen to the muscles, dilates the pupil, inhibits the digestive system, contracts the sphincters (circular obturator muscles) of some hollow organs (bladder, gastrointestinal tract), dilates the bronchi. The work of the sympathetic nervous system is enhanced by stressful stimuli. The parasympathetic nervous system performs a protective function; it helps to relax the body and restore its energy reserves. Irritation of parasympathetic fibers leads to weakening of the heart, contraction of the pupil, increased motor and secretory activity of the gastrointestinal tract, emptying of hollow organs, and narrowing of the bronchi. Thus, the sympathetic part of the nervous system adapts the body to intense activity. The parasympathetic department of the nervous system helps restore spent resources of the body. Each of them has a central and peripheral part.

Morphologically (by structure) Morphological differences between the sympathetic and parasympathetic systems are associated with the location of the last two neurons (central and peripheral) of the autonomic reflex arc. Such neurons are grouped into autonomic nuclei within the central nervous system and into autonomic ganglia in the peripheral nervous system. The sympathetic nuclei are located in the thoracic and upper lumbar parts of the spinal cord (in its lateral horns), and the parasympathetic nuclei are located in the brain stem and sacral part of the spinal cord (in the intermediate substance). In connection with the position of the central neurons, the sympathetic system is usually called the sterno-lumbar, or thoraco-lumbar (thoracale - thoracic; lumbale - lumbar), and the parasympathetic - craniosacral, or cranial-sacral (kranion - skull; sacrale - sacral). The sympathetic ganglia run along the spine, forming two (right and left) sympathetic chains. The chains are divided into cervical, thoracic, lumbar and sacral sections, each of which has several pairs of ganglia. It should be noted that in the reflex arc of the sympathetic nervous system the last neuron can be located not only in the nodes of the sympathetic trunk, but also in the nerve plexuses (ganglia celiaca - celiac ganglion, g.mesenterica - mesenteric ganglion, etc.). Parasympathetic ganglia are located either next to the innervated organ (extramural ganglia) or in its walls (intramural ganglia). Thus, it turns out that the preganglionic fibers of the sympathetic nervous system are short, and the postganglionic fibers are long. The opposite pattern is typical for the parasympathetic system. It should be noted that the number of nerve cells in the ganglia is several times greater than the number of preganglionic fibers (in the cervical sympathetic ganglion - 32 times, in the ciliary ganglion - 2 times). Accordingly, each of the preganglionic fibers branches and forms synapses on several ganglion cells. Thus, an expansion of the zone of influence of preganglionic fibers is achieved. From the above it is clear that there are no sympathetic centers in the brain. However, the smooth muscles and glands of the head have sympathetic innervation. Fibers coming from the superior cervical ganglia approach these organs. They penetrate the cranial cavity, forming plexuses around the internal carotid and vertebral arteries. In addition to the head, the cervical ganglia, together with the thoracic ganglia, innervate the organs of the neck and chest cavity. The lumbar ganglia send fibers to the abdominal organs, and the sacral ganglia send fibers to the rectum and genitals. Parasympathetic fibers of the cranial region pass through the oculomotor, facial, glossopharyngeal and vagus nerves. Let us recall that the parasympathetic fibers of the vagus nerve, leaving the cranial cavity, form synapses on the parasympathetic ganglia, which innervate most of the internal organs of the body. Fibers extending from the sacral region are associated with parasympathetic effects on the rectum, bladder, and genitals.

Mediators used in the transmission of nerve impulses. This difference can be called neurochemical, due to different mediators involved in the transmission of nerve impulses to the ANS. All neurons of the autonomic nuclei (i.e. central neurons) are acetylcholinergic. Thus, the transmitter that transmits nerve impulses in the autonomic ganglia (both sympathetic and parasympathetic) is acetylcholine. At the same time, the neurons of the autonomic ganglia differ in the transmitter they produce. In the sympathetic nervous system it is usually norepinephrine, and in the parasympathetic nervous system it is usually acetylcholine. Thus, in the sympathetic nervous system the signal is transmitted to the executive organ using norepinephrine, and in the parasympathetic nervous system - acetylcholine.

The brain (CB) is placed in the cranial cavity. Its dorsal (upper) surface is convex, while its ventral surface is more or less flattened. The main structures of the GM, according to its ontogenesis, have already been given in: this is the hindbrain, including the medulla oblongata, the pons and the cerebellum; midbrain; forebrain, consisting of the diencephalon and telencephalon. If you look at the GM as a whole, it can be divided into three main parts - the cerebral hemispheres, the brainstem and the cerebellum. The largest volume is occupied by the cerebral hemispheres, the smallest by the brain stem. The brainstem includes the medulla oblongata, pons, and midbrain; sometimes the diencephalon is also included in the trunk.

Rostral to the pons lies the midbrain. Its dorsal part is the roof, the ventral part is the cerebral peduncles. The cavity of the midbrain is the cerebral aqueduct. Between the cerebral peduncles there is the posterior perforated substance - holes through which blood vessels enter the medulla. On the border between the midbrain and forebrain in the dorsal part lies the posterior commissure, which is white matter. These are fibers that connect the right and left halves of the midbrain.

Located even more rostrally, the forebrain consists of the diencephalon and telencephalon. The main parts of the diencephalon are the thalamus, pineal gland and several structures of the hypothalamus: gray tubercle, optic nerve and optic chiasm, pituitary gland, mamillary bodies. The remaining structures belong to the telencephalon, consisting of two cerebral hemispheres. The fornix is ​​a bundle of fibers running from the telencephalon to the intermediate brain; transparent partition; The corpus callosum and the anterior commissure are fibers connecting the symmetrical areas of the forebrain. The cerebral hemispheres are divided into several lobes - frontal, parietal, occipital and temporal regions.

1. Structure and anatomical features of the brain stem.

In contrast to mixed (consisting of afferent sensory and efferent motor and autonomic fibers) spinal nerves, among the cranial nerves there are both mixed and only afferent or only efferent.

Only afferent (sensory) nerves are the I, II and VIII pairs.

Only efferent nerves - III, IV, VI, XI and XII pairs.

The remaining four pairs (V, VII, IX and X) are mixed.

The first two pairs (olfactory and optic nerves) are fundamentally different in nature and origin from the other nerves. They are outgrowths of the forebrain.

Let us characterize the remaining ten pairs of cranial nerves. They all arise from the brain stem. III and IV - from the midbrain; V - from the pons; VI, VII and VIII - from the groove between the pons and the medulla oblongata; IX, X, XI and XII - from the medulla oblongata. All nerves, with the exception of IV, exit the brain on the ventral (front) side. The IV nerve exits on the dorsal side, but immediately bends around the brainstem and passes to the ventral side. The neurons whose processes form the cranial nerves are similar to the neurons that form the spinal nerves. Next to the GM lie the cranial ganglia, similar to the spinal ganglia. They contain sensory neurons. Their peripheral processes form sensory fibers of mixed nerves. The central processes enter the brainstem and end on the nuclei in the brainstem. Such nuclei are called sensory nuclei of the cranial nerves. Their cells are similar to the interneurons of the dorsal horns of the SC. Also in the brain stem there are nuclei from which neurons extend axons that form efferent fibers. They come in two types. If fibers from these nuclei go to skeletal (voluntary) muscles, these are somatic-motor nuclei. They belong to the somatic NS. Their neurons are similar to the motor neurons of the anterior horns of the SC. If the fibers from these nuclei end on the autonomic ganglia, such nuclei are called vegetative. Their neurons are similar to the central autonomic neurons lying in the intermediate substance of the SC. All autonomic neurons of the brain stem belong to the parasympathetic part of the ANS (see Chapter 8).

So, depending on which fibers form the nerve, the latter may have one, two or more nuclei. Most of these nuclei (nuclei of the V - XII nerves) lie in the thickness of the medulla oblongata and the pons. In drawings, they are usually projected onto the bottom of the fourth ventricle - the rhomboid fossa. The nuclei of the III and IV nerves are located in the midbrain.

1. Efferent cranial nerves.

Efferent cranial nerves. The oculomotor (III pair), trochlear (IV pair) and abducens (VI pair) nerves control eye movements. Each of these nerves has a somatic motor nucleus, the fibers from which go to the muscles of the eye. The oculomotor nerve innervates the superior, inferior and internal rectus muscles, as well as the inferior oblique muscle of the eye; trochlear - superior oblique muscle of the eye; abductor - external rectus muscle of the eye. The nuclei of the III and IV nerves are located in the midbrain, the nucleus of the VI nerve is in the bridge under the facial tubercle in the rhomboid fossa (see 7.2.4). The oculomotor nerve has another nucleus - the autonomic one. It produces parasympathetic fibers that carry impulses that reduce the diameter of the pupil and regulate the curvature of the lens. There are close mutual connections between the nuclei of these three pairs of nerves, due to which combined eye movements and image stabilization on the retina are achieved. The accessory nerve (XI pair) controls the muscles of the larynx, as well as the sternocleidomastoid muscle of the neck and the trapezius muscle of the shoulder girdle. The nucleus is located in the medulla oblongata, part of it extends into the SC. Hypoglossal nerve (XII pair). Innervates the muscles of the tongue and controls its movements. The nucleus of this nerve extends almost throughout the entire medulla oblongata.

1. Mixed cranial nerves.

Mixed cranial nerves. The trigeminal nerve (V pair) contains afferent and efferent somatic motor fibers. Sensitive fibers innervate the skin of the face, teeth, mucous membranes of the oral and nasal cavities, carrying out pain, temperature, skin and muscle sensitivity. Motor fibers control the muscles of mastication and some muscles of the middle ear. The trigeminal nerve has three sensory nuclei, two of which are located in the medulla oblongata and pons, and one in the midbrain. The only motor nucleus of this nerve is located in the pons. The name “trigeminal” is due to the fact that it consists of three branches carrying information from three “floors” of the face - the forehead; nose, cheeks and upper jaw; lower jaw. Motor fibers pass in the inferior branch of the trigeminal nerve.

Facial nerve(VII pair) contains three types of fibers:

1) afferent sensory fibers bring impulses from the taste buds of the anterior two-thirds of the tongue. These fibers end in the nucleus of the solitary tract - the common sensory nucleus of the facial, glossopharyngeal and vagus nerves. It extends from the medulla oblongata into the pons;

2) somatic motor fibers innervate the facial muscles, as well as the muscles of the eyelids, and some muscles of the ear. These fibers come from the motor nucleus located in the pons;

3) autonomic parasympathetic fibers of the facial nerve innervate the submandibular and sublingual salivary glands, lacrimal glands, and glands of the nasal mucosa. They begin from the parasympathetic superior salivary nucleus, also located in the pons.

Glossopharyngeal nerve(IX pair) is similar in composition to the facial nerve, i.e. also contains three types of fibers:

1) afferent fibers bring information from the receptors of the posterior third of the tongue and end on the neurons of the nucleus of the solitary tract;

2) efferent somatic motor fibers innervate some muscles of the pharynx and larynx. The fibers begin in the nucleus ambiguus - the common motor nucleus for the glossopharyngeal and vagus nerves, located in the medulla oblongata;

3) efferent parasympathetic fibers begin in the inferior salivary nucleus and innervate the near-ear salivary gland.

Nervus vagus(X pair) is so called because of the extensive distribution of its fibers. It is the longest of the cranial nerves; with its branches it innervates the respiratory organs, a significant part of the digestive tract, and the heart. Just like the VII and IX nerves, it contains three types of fibers:

1) afferents carry information from the receptors of the previously mentioned internal organs and vessels of the chest and abdominal cavities, as well as from the dura mater of the brain and the external auditory canal with the auricle. These fibers carry information about the depth of breathing, pressure in blood vessels, stretching of organ walls, etc. They end in the nucleus of the solitary tract;

2) efferent somatic motor innervates the muscles of the pharynx, soft palate, and larynx (including those that control the tension of the vocal cords). The fibers begin in the double core;

3) efferent parasympathetic fibers begin from the parasympathetic nucleus of the vagus nerve in the medulla oblongata. The parasympathetic part of the vagus nerve is very large, so it is predominantly an autonomic nerve.

Of the sensory cranial nerves, only the vestibulo-auditory nerve(VIII pair). It brings impulses from the auditory and vestibular receptors of the inner ear to the central nervous system. The sensory nuclei of this nerve - two auditory (ventral and dorsal) and four vestibular (lateral, medial, superior and inferior) - are located on the border of the medulla oblongata and the pons in the area of ​​the vestibular field. The VIII nerve originates in the inner ear and consists of two separate nerves - the cochlear (auditory) nerve and the vestibular nerve.

In conclusion, it should be noted that the nuclei of the cranial nerves have many afferents and efferents. Thus, all sensory nuclei send efferents to the thalamus (diencephalon), and from there information enters the cerebral cortex. In addition, sensory nuclei transmit signals to the reticular formation of the brain stem. All motor nuclei receive afferents from the cerebral cortex as part of the corticonuclear tract. Finally, there are numerous connections between the cranial nerve nuclei themselves, which facilitates the coordinated activity of various organs. In particular, thanks to the connections between the sensory and motor nuclei, the arcs of the stem unconditioned reflexes (for example, gag, blinking, salivation, etc.), similar to the spinal unconditioned reflexes, are closed.

1. Reticular formation of the trunk.

In the middle part of the brain stem there is a reticular formation (RF) - a cluster of neurons of different sizes and shapes, separated by many fibers passing in different directions, reminiscent of a network (lat. reticulum). A large number of neurons of various types and sizes, grouped into nuclei, are localized in the Russian Federation. The common features of RF neurons are the form and nature of the organization of their connections. RF neurons are Golgi type I cells (with long axons). In this case, the axons have two branches running rostrally and caudally. Thus, both ascending and descending pathways begin from the RF cells, giving rise to numerous collaterals, the endings of which form synapses on neurons at all brain levels, i.e. one reticular neuron can send the impulses it generates simultaneously to various structures of the central nervous system.

The long branching dendrites of RF neurons are oriented predominantly in a plane perpendicular to the longitudinal axis of the brain. The RF is characterized by convergence (convergence) of afferentation from different sensory systems on one neuron. For example, sensory fibers carrying information from skin, visual and auditory receptors can form synapses on one reticular cell. In connection with such features of connections (both afferent and efferent), the reticular system was called non-specific, in contrast to specific systems that receive information from very specific structures and send it to specific “addresses”.

According to structural and functional criteria, the Russian Federation is divided into 3 zones: median - along the midline, medial - the internal sections of the trunk and lateral, the neurons of which lie near the sensory nuclei. In the medial parts of the RF of the medulla oblongata and the pons, large and even giant neurons are found, in the lateral parts of the same level small and medium-sized neurons are found; The midbrain contains predominantly small neurons. The median zone extends from the medulla oblongata to the caudal (posterior) parts of the midbrain. The structures included in this zone are united under the general name of the raphe nucleus. In the midbrain, the raphe nuclei are adjacent to the nuclei of the central gray matter, which are similar in a number of features to the nuclei of the Russian Federation. Neurons of the raphe nuclei are characterized by the presence of serotonin as a mediator. The RF receives the main volume of afferentation from sensory formations, such as sensory nuclei, spinal reticular tract, etc. At the same time, collaterals from a number of descending pathways also form synapses on RF neurons, in particular the corticospinal and rubrospinal tracts. RF also receives afferents from the cerebellum (from the tent nuclei). The RF efferents form two main fiber systems - ascending and descending. Ascending axons go to the forebrain - to the nonspecific nuclei of the thalamus (divencephalon), cerebral cortex; descending axons are sent to the SC. In addition, fibers from the RF go to the cerebellum. Numerous connections exist within the Russian Federation between its various formations, as well as between the nuclei of the Russian Federation and other stem structures. The RF is a brain system that regulates the functioning of the central nervous system and performs the most important integrative (unifying) functions. These functions are very numerous, although not fully explored. The RF plays a key role in controlling the overall level of activity of the nervous system, in particular in regulating the sleep-wake cycle. Through pathways connecting the RF with the spinal cord, it takes part in the control of posture, locomotion and goal-directed movements. The RF nuclei are also involved in regulation associated with vital reflexes. Thus, in the RF of the medulla oblongata and the pons there are breathing centers (divided into an inhalation center and an exhalation center), a vasomotor center (regulating vascular tone and heart function), a center for salivation and the secretion of other digestive juices, a swallowing center, as well as centers for such protective reflexes like coughing, sneezing, vomiting. Due to the presence of respiratory and vasomotor centers in the Russian Federation, the normal functioning of this department is vital. While damage, for example, to the structures of the telencephalon often causes almost no consequences due to the large compensatory capabilities of the central nervous system, even minor damage to the RF of the brain stem leads to severe impairment of body functions, and even death.

1. Medulla oblongata: gray matter nuclei and pathways.

The medulla oblongata lies at the base of the GM, being a continuation of the SC. In this regard, it combines the structural features of the SM and the initial section of the GM. The shape of the medulla oblongata resembles a truncated cone. Its length is approximately 30 mm, width at the base - 10 mm, at the top - 24 mm. Its lower border is the exit point of the first pair of spinal nerves. Above the medulla oblongata is the Varoliev pons, which outwardly looks like a constriction across the brain stem from the ventral side. The upper half of the medulla oblongata is occupied mainly by gray matter, the lower half by white matter. The medulla oblongata, together with the pons and cerebellum, makes up the hindbrain, the cavity of which is the fourth cerebral ventricle. The bottom of the IV ventricle on the dorsal side of the medulla oblongata and pons is the rhomboid fossa

Consider the ventral surface of the medulla oblongata:

The anterior median fissure divides it into two symmetrical halves, and several grooves separate various structures from each other. The IX - XII pairs of cranial nerves depart from the medulla oblongata. VI - VIII pairs emerge from the groove separating the medulla oblongata from the pons.

At the border with the SC, most of the fibers of this tract intersect, forming a pyramidal decussation. Laterally from the pyramids there are oval elevations - olives. In their depths there is gray matter - the nuclei of olives. This is where the spino-olivary tract coming from the SC ends. Olives also receive many other afferents - from the cerebral cortex, red nucleus, etc. These fibers form a dense capsule surrounding the nucleus. The olives themselves send their efferents to the cerebellar cortex (olivocerebellar tract). The olives, together with the cerebellum, are involved in maintaining posture and motor learning.

Let us now consider the dorsal side of the medulla oblongata:

Here it is divided into two symmetrical halves by the posterior median groove. On the sides of it lie two bundles - gentle (more medial) and wedge-shaped (more lateral). This is a continuation of the paths of the same name ascending from the SM (see 6.4). On the sides of the diamond-shaped fossa, thickenings are visible on the bundles - tubercles. Beneath them lie the tender and wedge-shaped nuclei, on which the fibers of the corresponding bundles end. The gray matter of the medulla oblongata is represented by nuclei. We are already familiar with most of them: 1) the nuclei of the trigeminal, facial, vestibulo-auditory, glossopharyngeal, vagus, accessory and hypoglossal nerves; 2) tender and wedge-shaped nuclei; 3) olive kernels; 4) nuclei of the reticular formation. White matter occupies a large volume. It includes the so-called transit paths, i.e. ascending and descending tracts passing through the medulla oblongata without interruption (without forming synapses on its neurons). These include all the spinal tracts with the exception of the gentle and sphenoid fasciculi, as well as the spino-olivary tract, which end directly in the medulla oblongata. Transit tracts occupy the ventral and lateral parts of the medulla oblongata.

In addition, new tracts begin here: 1) the lower cerebellar peduncles. These pathways connect the cerebellum with other brain structures (the cerebellum has three pairs of legs in total). The inferior peduncles include the olivocerebellar tract, the posterior spinocerebellar tract, as well as fibers from the vestibular nuclei of the brainstem; 2) ascending tract - medial loop, or medial lemniscus (lat. lemnisk - loop). Its fibers are formed by the axons of the cells of the tender and cuneate nuclei, which first pass to the other side and then go to the thalamus. The spinothalamic tract, as well as fibers from the sensory nuclei of the brain stem (nucleus of the solitary tract and nuclei of the trigeminal nerve), also ending in the thalamus, join the medial lemniscus. As a result, this entire system conducts taste, visceral and various types of somatic (pain, skin, muscle) sensitivity into the diencephalon.

Thus, the medulla oblongata performs reflex and conductive functions. The conductor function is that ascending and descending pathways pass through the brain stem (including the medulla oblongata), connecting the overlying parts of the brain, up to the cerebral cortex, with the spinal cord. Collaterals from these pathways can end on the nuclei of the medulla oblongata and pons. The reflex function is associated with the nuclei of the brain stem, through which reflex arcs are closed. It should be noted that in the medulla oblongata (mainly in the reticular nuclei) there are many vital centers - respiratory, vasomotor, centers of food reflexes (salivary, swallowing, chewing, sucking), centers of protective reflexes (sneezing, coughing, vomiting), etc. Therefore, damage to the medulla oblongata (trauma, swelling, hemorrhage, tumors) usually leads to very serious consequences.

1. Midbrain: gray matter and pathways.

The midbrain, mesencephalon, is the smallest part of the brain, its length is approximately 2 cm. The cavity of the midbrain - the cerebral (Sylvian) aqueduct has a diameter of about 1 mm. Two pairs of cranial nerves emerge from the midbrain - the oculomotor (III pair) and the trochlear (IV pair). Let us recall that the trochlear nerve leaves the brain on the dorsal side, then goes around the cerebral peduncles and passes to the ventral side. On the dorsal side of the midbrain there is a roof, consisting of two pairs of tubercles - the inferior and superior colliculi of the quadrigeminal. They are separated by mutually perpendicular grooves. Between the upper and lower colliculi there are commissures of the colliculi - fibers connecting the right and left colliculi. In addition, from each tubercle there is a handle of the hillock - fibers going to the thalamus. The cerebral peduncles are located on the ventral side. They emerge from the bridge, head forward and, gradually diverging to the sides, plunge into the thickness of the cerebral hemispheres. Between the legs lies the interpeduncular fossa, in the bottom of which there are many small holes through which blood vessels pass. This area is called the posterior perforated substance. The cerebral peduncles are divided into a tegmentum and an underlying base. The boundary between them is the substantia nigra.

The roof of the brain consists of gray matter, the base - of white matter (descending tracts only), in the tegmentum, among the fibers of the white matter, lie the nuclei of gray matter.

Roof of the midbrain . The superior colliculi have a layered structure (consist of seven cell layers), i.e. They are characterized by a cortical organization. Their afferents are, first of all, the fibers of the optic tract, as well as the spino-tectal tract, the inferior colliculus, and the cerebral cortex. The efferents are fibers of the tectospinal tract, fibers going to the nuclei of the oculomotor nerves, as well as the handles of the superior colliculus. These connections contribute to the main function of the superior colliculi - organizing movements in response to a new stimulus (turning the head, eyes, ears towards the stimulus). This innate reaction is called the orienting reflex. The inferior colliculus has several nuclei, as well as a small area with cortical organization. In phylogeny, these hillocks appear only in mammals and are auditory centers. Their afferents are auditory fibers of the lateral lemniscus. Efferents as part of the handles of the posterior colliculi go to the thalamus.

Tire . Most of the mesencephalic nuclei lie here:

1. Nuclei of the oculomotor and trochlear nerves.

2. Central gray matter (CGM) lies in the center of the midbrain, around the cerebral aqueduct, forming a layer of about 2 mm. The CSV closely interacts with the raphe nuclei, controlling the functioning of their neurons. One of the functions of the central nervous system is associated with the regulation of pain sensitivity. When its neurons are irritated, pain relief is possible due to influences on areas of the spinal cord associated with switching pain signals. CSV can have a number of inhibitory effects on the hypothalamus and cerebral cortex. In addition, the central gray matter is considered to be one of the main centers of sleep.

3. Red core It got its name because it has a pinkish color due to the abundance of blood vessels in it. This large ellipsoidal nucleus extends along the entire length of the midbrain.

It is divided into two parts - anterior parvocellular And posterior magnocellular. The anterior part is an evolutionarily young formation, maximally developed in humans; the posterior one is phylogenetically ancient and is small in humans.

Afferents of the red nucleus- this is the cerebral cortex, cerebellar nuclei, basal ganglia of the telencephalon, etc.

Concerning efferents, then first of all we should note the rubrospinal tract, already known to us, which starts from the magnocellular part of the red nucleus. Efferents from the parvocellular part go to the inferior olive, motor nuclei of the cranial nerves, thalamus, and basal ganglia. The red nucleus is the most important formation of the extrapyramidal system. Traditionally, the red nucleus is considered as the efferent link of this system (activation of flexor muscles and inhibition of extensors of the limbs).

It is difficult to underestimate the functions and role of the human brain. Humans are characterized by: coherent speech, the ability to fantasize, the ability to analyze, remember facts, distinguish melodies, pass on experience to generations, and much more. The human body is a complex, ideally adjusted structure that ensures physical activity, vital functions, and basic mental functions: thinking, perception, memory, speech, etc.

The obvious connection between the brain and reflex sensory activity stimulates scientists to continue studying the brain and its functions, where one of the pressing issues remains the role of gray matter in human life and in the formation of human intelligence.

General information about gray matter

The human central nervous system (CNS) is one of the most complex structures of the body; it plays an extremely important role - it ensures the functional integrity of the body and its relationship with the outside world. The central nervous system consists of the brain and spinal cord and their protective membranes, which, in turn, consist of gray and white matter.

The gray substance (lat. substantia grisea) is responsible for most of the functions of higher nervous activity in humans. Thanks to it, a person perceives the external environment, hears, sees, speaks, and most importantly, a person can express an attitude, show sympathy or negative emotions, exhibit types of human behavior, empathy, etc.

The substance consists of approximately 86 billion neurons; of course, this number is extremely approximate, since modern medicine does not yet have the ability to count the exact number of nerve cells.

The white substance or (lat. substantia alba) serves mainly to transmit signals and ensures the interconnection of both hemispheres, and also transfers information from the cerebral cortex to the nervous system.

Clusters of neurons form gray matter. Each nucleus has a corresponding responsibility and function: visual, auditory, circulation, breathing, movement, urination, etc.

Consists of gray matter nuclei that form the corresponding centers. Substantia grisea is one of the main components of the spinal cord, and its nuclei are located in the cerebellar cortex and in the internal structures of the cerebrum (medulla oblongata, thalamus, hypothalamus, etc.).

Gray matter appears in the form of a membrane of the brain, under which there is white, however, in the spinal cord, substantia grisea is located in the inner part of the spinal system, enveloping a narrow central canal filled with cerebrospinal fluid, the substance forms the outline of the letter H, and it is already covered with white matter.

Structure of gray matter

Substantia grisea is an ideal structure consisting of:

• neurons;
• dendrites;
• unmyelinated axons;
• glial cells;
• thin capillaries.

The latter color the bark brown and, contrary to popular belief, the substance is not gray, but grey-brown. Numerous labyrinth-like depressions and bulges form convolutions known as cerebral gyri. The main function of gray matter is to ensure communication between the human body and the outside world, as well as to regulate reflexes and ensure higher mental functions.

And if the substantia grisea consists of neurons, then the substantia alba appears in the form of myelin-covered axons (neuron processes), which act as conductors and serve to transmit signals and provide communication between the hemispheres and nerve centers. The myelin sheath gives the substance its characteristic white color.

The gray substance in the spinal structure resembles the contours of the letter H or the wings of a butterfly. Depending on their location and functions, gray pillars are divided into: rear, front and side. The lateral parts of the dorsal region, in turn, are divided into:

• Posterior - consist of intermediate nerve cells. Receive signals from ganglia.
• The anterior ones consist of motor neurons. The main function is to ensure muscle tone.
• Lateral - consist of sensory and visceral neurons. Responsible for motor functions.

Functions of gray matter

The work of the central nervous system provides a large number of connections in the body that perform two main functions: control of muscle activity (motor reflex) and provision of sensory perception (sensory reflexes) and higher mental functions: memory, speech, emotions.

The functions of the substantia grisea are determined by its location, for example:

1. In the cerebral cortex, the substance is responsible for connecting the body with the outside world, and also carries information and regulates the activity of internal organs, is responsible for ensuring higher nervous activity, thanks to which a person is able to think, remember, perceive, etc.
2. In the medulla oblongata, the nuclei of the substance regulate motor processes, balance, ensure coordination of movements, and also regulate metabolism, respiratory processes and blood supply.
3. In the cerebellar cortex, the gray nuclei are responsible for coordination of movements and orientation in space.
4. In the diencephalon, the nuclei are responsible for controlling the activity of internal organs, regulating reflexes and body temperature.
5. In the telencephalon, the nuclei provide motor, reflex control and regulation of higher mental functions: coherent speech, vision, smell, taste, hearing, touch.

The spinal cord is a complex structure that has the following functions: reflex, motor, sensory and conductive. The first three functions are assigned to the gray matter, and the third - to the white matter.

1. Reflex function - regulation of unconditioned reflexes: sucking reflex, knee reflex, instant reaction to painful stimuli, etc.
2. Motor function – control of muscle reflexes associated with the motor system. The corresponding cells of the spinal cord send signals to a specific group of muscles, prompting one or another action, thanks to which we can purposefully turn our head, move our neck, raise and lower our arms, and walk.
3. Sensory function is the transmission of an impulse coming from the afferent fibers of the torso to the parts of the brain, from where the command comes, containing a reaction to the stimulus.
4. The conductor function is to ensure the passage of an impulse to the brain, and from there, the passage of an action command going to the corresponding organ. Regulated by the white substance.

The gray substance ensures the normal functioning of a person, his interaction with the outside world, types of human activity, is the basis of cognitive and sensory perception, as well as the basis of motor, reflex, regulatory and all mental functions.

How gray matter influences some human abilities

The gray tissue of the brain, regulating the processing of signals from the outside and generating effector impulses, is not only responsible for the functioning of the entire human nervous system, but also affects his abilities: mental, cognitive, physical, etc.

Various experiments by scientists have shown that a person’s abilities depend on the volume of the gray substance, while changes in the amount of white substance did not show any noticeable changes.

Experiments by British scientists have shown that the thinner the cerebral cortex, therefore, the smaller the volume of gray substance, the worse a person copes with solving logical problems, the less various abilities he has, and also with a low volume of substance, subjects often had problems with reaction speed , speech dysfunctions, memory problems and poor intellectual abilities.

At the same time, studies have shown that learning foreign languages, memorizing poetry, scientific or artistic works, and playing music affect the enlargement of the cerebral cortex. The longer and more intense the learning process, the greater the volume of gray substance becomes, therefore, the more abilities, including mental ones, a person displays.

A decrease in the amount of gray matter is affected by:

• a person’s lifestyle is a sedentary, inert, inactive, from a physical and mental point of view, way of life;
• abuse of bad habits - alcohol, drug addiction and smoking reduce the volume of gray substance.

For example: those suffering from alcoholism experience a significant decrease in the amount of brain tissue, which is reflected in behavior and mental functions: incoherent speech, problems with memory and perception, inhibition of thought processes.

Gray matter and intelligence

Currently, the scientific world is divided into two fronts:

1. The first argue that the mass and volume of the brain affect a person’s mental abilities.
2. The latter are confident that the volume of gray matter plays a secondary role.

At different times, scientists from different countries tried to determine the connection between the substantia grisea and intelligence, however, it is necessary to take into account the fact that the study of the brain, due to the structure and location of the organ, is a rather difficult process, and much about the functions of the brain still remains unexplored and unknown to a person.

We can say with confidence that a weak connection between mental, analytical abilities and brain size was discovered by scientists a couple of decades ago, however, other scientists have proven in experiments that the level of intelligence does not depend on the weight or size of the brain as a whole, but on the size of the front lobes of the brain.

Modern scientists suggest that human IQ is a complex and multifaceted concept, and in the process of developing human intelligence, various structures are involved, where the speed of transmission of nerve impulses or the number of connections between nerve cells plays an important role.

Another group of scientists found that people with high intelligence have larger gray matter volume. However, this only led to another hypothesis that a certain percentage of the volume of the substantia grisea is associated with a person’s intellectual abilities.

There are many hypotheses related to the question, but to date the scientific world has not yet given an experimentally proven, unambiguous answer.

One thing is for sure - the additional volume of gray matter allows you to process information more productively and quickly; damage and damage to the gray matter, depending on the location, leads to muscle, sensory and neurological disorders.

Nervous system

The nervous system unites parts of the body (integration), ensures the regulation of various processes, coordination of the work of organs and interaction of the body with the external environment. It perceives a variety of information coming from the external environment and internal organs, processes it and generates signals that determine adequate responses.

Anatomically, the nervous system is divided into central (brain and spinal cord) and peripheral (peripheral nerve ganglia, nerve trunks and nerve endings). From a physiological point of view, a distinction is made between the autonomic (autonomic) nervous system, which innervates internal organs, glands, and blood vessels, and the somatic (cerebrospinal) nervous system, which regulates the activity of the rest of the body (skeletal muscle tissue).

Nervous system development

The development of the nervous system originates from the neuroectoderm (neural plate), which forms the neural tube, neural crest, and neurogenic placodes. The spinal cord and brain develop from the neural tube, in which the following layers differentiate:

Internal limiting membrane;

Ependymal layer;

Raincoat layer;

Edge veil;

Outer organic membrane.

The source of all cells The CNS are the matrix (ventricular) cells of the inner layer. They are concentrated near the internal limiting membrane, actively multiply and move. Cells that have completed proliferation - neuroblasts, as well as glioblasts capable of proliferation - move into the mantle layer. Some of the ventricular cells remain in situ, and in the future this is the future ependyma.

Neuroblasts give rise to all neurons of the central nervous system; after migration, they lose their ability to proliferate. Glioblasts become the precursors of macroglia and are capable of proliferation.

The rigidity of the brain organization is determined by two factors: targeted cell migration and directed growth of processes. The mechanism of directed movements is due to chemotropism, which occurs along a pre-marked path. At certain stages of ontogenesis, programmed cell death occurs. The volume of the subpopulation of dying neurons is estimated in the range of 25-75%. At the same time, the cellular elements of the ganglion plate form the spinal and vegetative nodes.

Spinal cord

The spinal cord is a section of the central nervous system, which is located in the spinal canal and has the appearance of a rounded cord, slightly flattened in the dorso-abdominal direction. In the center of the spinal cord lies the central spinal canal, lined with ependymal glia.

The spinal cord, like the brain, is covered by three meninges:

Inner - pia mater with vessels and nerves in its loose connective tissue. It is directly adjacent to the spinal cord.

This is followed by a thin layer of loose connective tissue - the arachnoid membrane. Between these membranes there is a subarachnoid (subarachnoid) space with thin connective tissue fibers connecting the two membranes. This space with cerebrospinal fluid communicates with the ventricles of the brain.

The outer shell is the dura mater, consisting of dense connective tissue, fused with the periosteum in the cranial cavity. In the spinal cord there is an epidural space between the periosteum of the vertebrae and the dura mater, filled with loose fibrous connective tissue, which gives some mobility to the membrane. Between the dura mater and the arachnoid there is a subdural space with a small amount of fluid. The subdural and subarachnoid spaces are covered from the inside with a layer of flat glial cells.

The spinal cord consists of two symmetrical halves, delimited from each other in front by the median fissure, and behind by the median sulcus.

In a cross section, gray and white matter are easily distinguished.

Gray matter located in the central part, surrounded by white matter.

Gray matter in cross section has the shape of butterfly wings. The projections of gray matter are called horns: there are anterior, posterior and lateral horns. There is an intermediate zone between the anterior and posterior horns. The horns are actually columns running along the spinal cord.

The gray matter of both symmetrical halves is connected to each other in the region of the spinal canal by a central gray commissure (formed by commissures).

Gray matter is formed by the bodies of nerve cells, their dendrites and partly axons, as well as glial cells.

Nerve cells are located in the gray matter in the form of not always sharply demarcated clusters - nuclei. Based on the location of neurons, the nature of their connections and function, B. Rexedom identified 10 plates in the gray matter of the spinal cord. The topography of the nuclei corresponds to the topography of the plates, although they do not always coincide.

Depending from axon topography Neurons of the spinal cord are divided as follows:

♦ Internal - neurons whose axons end within the gray matter of a given segment of the spinal cord.

♦ Tufted - their axons form bundles of fibers in the white matter of the spinal cord.

♦ Radicular - their axons exit the spinal cord as part of the anterior roots.

In the posterior horns there are: spongy layer, gelatinous substance, dorsal horn nucleus proper and thoracic nucleus.

Spongy layer stretches continuously along the spinal cord, forming the dorsal lobe of the dorsal horn, which corresponds to lamina I, characterized by a glial skeleton, which contains a large number of small interneurons. These neurons respond to pain and temperature stimuli and send fibers to the spinothalamic tract on the opposite side. Among these neurons are cells containing substance P and enkephalin.

In the gelatinous substance, or Roland's gelatinous substance(lamina II, III), glial elements predominate. The nerve cells here are small and there are few of them. Axons coming from the posterior cord and fibers of pain and tactile sensitivity approach them. The axons of the neurons of this layer either end within a given segment of the spinal cord (enter the marginal belt of Lissauer, which forms transverse and longitudinal connections on the surface of the gelatinous substance), or go into their own bundles or to the thalamus, cerebellum, and inferior olives. Neurons in this layer produce enkephalin, an opioid-type peptide that inhibits pain effects.

The main significance of the gelatinous substance is the implementation of an inhibitory effect on the functions of the spinal cord by controlling the sensory information entering it: cutaneous, partially visceral and proprioceptive.

Own core consists of interneurons that receive afferent impulses from the spinal ganglia and descending fibers of the brain. Their axons pass through the anterior white commissure to the opposite side and ascend to the thalamus, just as the substantia gelatinosa is responsible for exteroceptive sensitivity.

The thoracic nucleus of the posterior horn (Clark's nucleus) is located in plates VII. It is formed by neurons to which thick myelinated sensory neuron collaterals supply, delivering proprioceptive sensory sensation from joints, tendons and muscles. The axons of Clark's nucleus cells form the posterior spinocerebellar tract.

In the intermediate zone VI and partially VII plates are located the external and internal basilar nuclei. They process the bulk of information coming from the brain and transmit it to motor neurons. On the cells of the outer nucleus, thick fast-conducting axons are interrupted, originating from the largest and giant pyramids of the motor zone of the cerebral cortex. Thin, slow-conducting fibers project to the neurons of the inner nucleus. In humans, about 90% of the fibers of the corticospinal tract end on the neurons of the basilar nuclei.

The lateral horns contain: medial and lateral nuclei.

The lateral nucleus (Th I - L II) contains neurons of the autonomic reflex arc - the center of the sympathetic department. The sympathetic nucleus includes axons of the pseudounipolars of the spinal ganglion, which carry visceral sensitivity. The second group of axons comes from the medial nucleus of the lateral horn. The axons of neurons in the lateral nucleus give rise to preganglionic fibers that exit the spinal cord through the ventral roots.

The medial nucleus (S II - Co III) is located in the intermediate zone, where the lateral horns are absent - it receives impulses from the sensitive neurons of the autonomic reflex arc.

In addition, the Onufrovich nucleus is located in the lateral horns of the sacral segments (S2 - S4) of the spinal cord. It contains neurons of the parasympathetic division of the autonomic nervous system, which are involved in the innervation of the pelvic organs.

Lamina VII contains Renshaw interneurons, which are necessary for the implementation of motor function. They receive an excitatory impulse from the axon collagers of motor neurons and inhibit their function. This is important for the coordinated work of motor neurons and the muscles they innervate for alternate flexion and extension of the limbs.

The interstitial nucleus of Cajal is localized in lamina VIII. Its interneurons switch information from afferent neurons to motor neurons. The axons of the neurons of this nucleus are part of their own bundles and form collateral connections on several segments.

The periependymal gray matter corresponds to the X plate, is located throughout the spinal cord and is formed by interneurons of the autonomic nervous system.

The anterior horns contain multipolar motor neurons (lamina IX), which are the only executive cells in the spinal cord that send information to the skeletal muscles. They are combined into nuclei, each of which usually extends into several segments. The motor neurons end on:

♦ Axon collaterals of pseudounipolar cells, forming two-neuron reflex arcs with them.

♦ Axons of interneurons, the bodies of which lie in the dorsal horns of the spinal cord.

♦ Axons of Renshaw cells forming inhibitory axosomatic synapses. The bodies of these small cells are located in the middle of the anterior horn and are innervated by collaterals of motor neuron axons.

♦ Fibers of the descending tracts of the pyramidal and extrapyramidal systems, carrying impulses from the cerebral cortex and brainstem nuclei.

According to classical concepts, motor neurons in the spinal cord are distributed over 5 motor nuclei.

Medial - anterior and posterior - are present throughout the spinal cord and innervate the muscles of the trunk.

Lateral - anterior and posterior - are localized in the cervical and lumbar thickenings, innervate the flexors and extensors of the limbs.

Central core - located in the lumbar and cervical regions, innervates the muscles of the limb girdles.

White matter- divided by the anterior and posterior roots into symmetrical ventral, lateral and dorsal funiculi. It consists of longitudinally running nerve fibers (mainly myelin), forming descending and ascending pathways (tracts), and astrocytes. Each tract is characterized by a predominance of fibers formed by neurons of the same type.

The pathways include 2 groups: propriospinal and supraspinal.

Propriospinal pathways- the spinal cord's own apparatus, formed by the axons of interneurons that communicate between the segments of the spinal cord. These pathways pass mainly at the border of the white and gray matter as part of the lateral and ventral funiculi.

Supraspinal pathways- provide connection between the spinal cord and the brain and include the ascending and descending spinal cerebral tracts.

Pain, temperature, deep and tactile sensitivity are carried out along the ascending pathways. These are the spinothalamic tract, the dorsal and ventral spinocerebellar tracts, and the gentle and cuneate fasciculi.

The spinal cerebral tracts provide transmission of impulses to the brain. Some of them (20 in total) are formed by the axons of cells of the spinal ganglia, while the majority are represented by the axons of various interneurons, the bodies of which are located on the same or on the opposite side of the spinal cord.

Cerebrospinal tracts include pyramidal and extra-rapyramidal systems.

The pyramidal system is formed by long axons of pyramidal cells of the cerebral cortex, which at the level of the medulla oblongata mostly move to the opposite side and form the lateral and ventral corticospinal tracts. The pyramidal system controls precise voluntary movements of skeletal muscles, especially the limbs.

The extrapyramidal system is formed by neurons, the bodies of which lie in the nuclei of the midbrain and medulla oblongata and the pons, and the axons end on motor neurons and interneurons. This system primarily controls the contraction of the tonic muscles, which are responsible for maintaining body posture and balance.

The extrapyramidal descending tracts are represented by the rubrospinal tract, originating from the red nucleus and conducting impulses from the cerebellar nuclei, as well as the tectospinal tract, starting from the tegmentum and conducting impulses from the visual and auditory tracts, as well as the vestibulospinal tract, originating from the nuclei of the vestibular nerve and carrying impulses of a static nature.