The spinal cord is the most unique organ in the human body. It is located in the spinal canal and is responsible for various systems. What are the functions of the spinal cord? How is it built? What does it consist of?

The spinal cord is part of the central nervous system. Thanks to it, all nerve impulses and signals are transmitted in the human body. This part of the body is significantly small compared to other parts. It weighs only 35-38 grams, although it reaches 45 centimeters in length.

Externally, the spinal canal resembles a white cord, slightly flattened towards the back. It begins in the opening in the medulla oblongata (occipital zone), and ends in the lumbar region. The entire spinal cord is divided into segments by grooves. Inside it is filled with cerebrospinal fluid.

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All pathways consist of white and gray matter. Gray matter is located closer to the center of the spinal canal, and white matter is located closer to the edge. If we consider a vertebral cross-section, its shape will resemble that of a butterfly. On the gray and white matter I can distinguish the anterior and posterior horns. Each pair of them is responsible for delivering signals from neurons to the brain. The dorsal horns are responsible for connecting all the neurons of the spinal cord with each other.

Human spinal column

Axons, the motor roots of the spinal cord, extend from the anterior pair of horns. They are distributed throughout the intervertebral spaces. Sensitive roots approach the posterior horns. Connecting in the intervertebral space, they form the spinal nerves. Each person has 31 pairs of such nerves in the body. In accordance with the way the spinal nerves are distributed along the spinal column, the entire spinal cord is divided into segments. It goes like this:

• 8 segments in the cervical region;
• 12 in the chest;
• 5 in the lumbar;
• 5 sacral segments;
• 1 coccygeal segment.

There are 31 segments in total.

Three columns can be distinguished within the white matter. Inside each one there are processes of neurons, or pathways. Some paths are ascending and others are descending.

The last three segments of the spine, that is, the lumbar, sacral and coccygeal, form the cauda equina. The cauda equina, like the entire brain, is covered with a three-layer membrane:

• hard;
• arachnoid;
• soft.

Pathway systems

All pathways in our body are divided into three systems:

• associative;
• afferent;
• efferent.

Association pathways are the shortest connections of the spinal cord. These pathways are designed to connect all the spinal cord neurons between segments.

Afferent pathways have a sensitive function. Being ascending pathways, they transmit received information from external receptors to the brain.

Efferent pathways are descending. This type of pathway carries brain signals to all neurons in the body.

Basic functions of the spinal cord

The spinal cord is responsible for two main functions:

• reflex;
• conductor.

Interestingly, each segment is responsible for the activities of different organs. For example, the cervical and thoracic segments are responsible for the work of the arms and organs located in the sternum. The lumbar segment controls the actions of the internal digestive organs and the muscular system. And the sacral segment is responsible for the functioning of the pelvic organs and legs.

The role of the reflex function

Thanks to the reflex function, a person has an instant reaction to the sensation of pain. For example, if a person touches a hot iron, it does not take him several minutes to realize that it is hot and remove his hand. This happens in a split second. All this is possible thanks to the reflex function of the spinal cord.

We can also observe the manifestation of this function in the example of the knee reflex.

The role of the conduction function

The conductor function is to transmit impulses from the brain to the neurons of each organ, and vice versa, to collect information coming from the outside and transmit it to the brain.

If we decide to get up, go somewhere, take something, we do it instantly, without even thinking. All this is possible thanks to the conductive function of the brain.

Diseases of the lower segment of the spinal cord

The inferior zone or cauda equina is devoid of the spinal cord. Only cerebrospinal fluid and nerve bundles remain there. However, if compression of these endings occurs, various disorders of the musculoskeletal system may develop. In another way, experts call this disease cauda equina.

Horsetail is characterized by the occurrence of unpleasant symptoms. A person begins to feel pain in the lumbar area, and general muscle weakness appears. People often notice that the body’s ability to quickly respond to stimuli is significantly reduced. Inflammation and temperature fluctuations may also occur. Over time, it may become difficult to walk and sit for long periods of time.

If the cauda equina is damaged, emergency surgery may even be required. If major surgery is not performed promptly, the digestive and urinary systems may be damaged, and in rare severe cases, paralysis of the legs may even develop.

Causes of the syndrome

A cauda equina can develop as a result of a narrowing of the lower spinal canal. This may happen for the following reasons:

• spinal injuries;
• cancerous tumors;
• meningiomas;
• metastases in the spine;
• inflammatory diseases;
• undergone operations.

With internal subluxations in the lumbar regions, the formation of an epidural hematoma is possible. An epidural hematoma is formed as a result of rupture of blood vessels and bleeding. The accumulation of blood can put pressure on the cauda equina, thereby causing problems with the system.

In more than 15 percent of cases, the cauda equina is compressed as a result of a herniated disc. Most often, this diagnosis is made to men who have reached the age of forty. An enlarged hernia puts pressure on the spinal cord, leading to damage to the spinal column.

The important role of the spinal cord in the human body

The brain is the most important organ of the human body. Without it, no movements, sensations or reactions would be possible. It is a kind of control center of the entire body, of all nerve endings. Without the reliable functioning of this organ, we would not be able to make a single movement or feel anyone’s touch.

Although the brain also plays an important role, its functions would not be so complete without the spinal cord. For example, in order to see what is happening around us, we need the work of the optic nerve, which obeys the brain. But only thanks to the guidance of the spinal cord, we can look in different directions by turning our pupils. The same is true with the ability to cry. Although we can experience negative emotions without the spinal cord, we cannot cry with its participation.

When some actions occur consciously, we need instructions coming from the brain. When a process becomes automatic, it occurs at the reflex level with the help of the spinal cord. Consequently, this small but very important organ requires our close attention and careful treatment!

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Phylogenesis of the nervous system is the history of the formation and improvement of the structures of the nervous system. The simplest single-celled organisms do not yet have a nervous system, and communication with the environment is carried out using fluids located inside and outside the body; this is a humoral, pre-nervous form of regulation. Subsequently, the nervous system and another form of regulation arise - nervous. Stage 1~diffuse (network) nervous system. At this stage (coelenterates), the nervous system, such as hydra, consists of nerve cells, the numerous processes of which connect with each other in different directions, forming a network that diffusely permeates the entire body of the animal. Stage 2 - nodal nervous system. At this stage (higher worms), nerve cells come together into separate clusters or groups, and from clusters of cell bodies, nerve nodes - centers are obtained, and from clusters of processes - nerve trunks - nerves. Stage 3 - tubular nervous system. In lower multicellular organisms it is associated with smooth muscles. This is the central nervous system in chordates (lancelet). In vertebrates and humans, the trunk cord becomes the spinal cord. Thus, the appearance of the trunk brain is associated with the improvement, first of all, of the animal’s motor weapons.

At the first stage of development, the brain consists of three sections: posterior, middle and anterior.

With each stage of evolution, new centers arise, subordinating the old ones. There seems to be a movement of functional centers to the head end and the simultaneous subordination of phylogenetically old rudiments to new ones..

Improvement of receptors leads to progressive development of the forebrain, which gradually becomes the organ that controls all animal behavior Ontogenesis- This is the gradual development of a particular individual from the moment of birth to death. The formation of the nervous system can be observed already in a two-week-old embryo in the form of a plate formed on its dorsal surface in the mass of the germ layer - the ectoderm, from which the nervous system develops. In the fourth week of embryonic development, the anterior end of the brain tube, developing unevenly, forms an expansion in the form of three bubbles. Subsequently, the anterior and posterior vesicles are laced, and thus five brain vesicles arise, from which the main parts of the brain are formed. 19 The spinal cord develops more rapidly than the brain

.

So, already in a three-month-old embryo it is basically formed. At the time of birth, the fetal brain is externally sufficiently formed. All the grooves and convolutions that exist in an adult are present in a reduced form in the newborn’s brain.

. The weight of a newborn baby’s brain is usually 370 g for boys and 360 g for girls.. Below are the spinal cord membranes that surround the roots of the lower spinal nerves. If we consider a cross section of the spinal cord, we can see that its central part is occupied by a butterfly-shaped gray matter composed of nerve cells . In the center of the gray matter, a narrow central canal is visible, filled cerebrospinal fluid. Located outside the gray matter. white matter. It contains nerve fibers that connect spinal cord neurons to each other and to neurons in the brain. Spinal nerves depart from the spinal cord in symmetrical pairs; there are 31 pairs of them. Each nerve begins from the spinal cord in the form of two cords, or roots, which, when connected, form a nerve. Spinal nerves and their branches travel to muscles, bones, joints, skin and internal organs. The spinal cord in our body performs two functions: reflex and conductive Reflex function of the spinal brain The conductors of the spinal cord, which make up its white matter, transmit information in the ascending and descending directions. An impulse about an external influence is sent to the brain, and a certain sensation is formed in a person (for example, you are stroking a cat, and you have a feeling of something soft and smooth in your hand). Centrifugal fibers emerge from the spinal cord, along which impulses go to the organs and tissues. Damage to the spinal cord disrupts its functions: areas of the body located below the site of injury lose sensitivity and the ability to move voluntarily. The brain has a great influence on the activity of the spinal cord. All complex movements are under the control of the brain: walking, running, work. The spinal cord is a very important anatomical structure. Its normal functioning ensures all human life. Knowledge of the structure and functioning of the spinal cord is necessary for diagnosing diseases of the nervous system.

Peripheral nerves. Structure, plexuses

The human nervous system is divided into central, peripheral and autonomic parts. The peripheral part of the nervous system is a collection of spinal and cranial nerves. It includes ganglia and plexuses formed by nerves, as well as sensory and motor endings of nerves. Thus, the peripheral part of the nervous system unites all nerve formations that lie outside the spinal cord and brain. This association is to a certain extent arbitrary, since the efferent fibers that make up the peripheral nerves are processes of neurons whose bodies are located in the nuclei of the spinal cord and brain.Structure nerves Peripheral nerves are made up of fibers , having different structures and unequal functionally. Depending on the presence or absence of the myelin sheath, fibers are myelinated (pulpless) or non-myelinated (pulpless). Nerves have a system of their own membranes. The outer membrane, the epineurium, covers the nerve trunk from the outside, delimiting it from the surrounding tissues, and consists of loose, unformed connective tissue. The loose connective tissue of the epineurium fills all the spaces between individual bundles of nerve fibers. The next layer, the perineurium, covers covers individual nerve fibers with a thin connective tissue sheath. The cells and extracellular structures of the endoneurium are elongated and oriented predominantly along the nerve fibers. The amount of endoneurium inside the perineural sheaths is small compared to the mass of nerve fibers. Depending on the structure of the bundles, two extreme forms of nerves are distinguished: small-beam and multi-beam.

The first is characterized by a small number of thick bundles and weak development of connections between them. The second consists of many thin bundles with well-developed interfascicular connections. Nerve plexuses- This is the largest initial section of the peripheral nervous system. Nerve plexuses are formed directly from the spinal cord, the anterior (motor) and posterior (sensitive) nerve roots emerge. The anterior and posterior roots on each side then fuse to form the spinal nerve trunk, which exits through the bony intervertebral foramen. Then the individual trunks split into a large number of branches, already outside the spinal canal, and they, in turn, are also closely intertwined, forming many connections. The largest nerves then depart from the resulting nerve plexus, which are directly sent to various organs and tissues. In the human body there are several groups nal nerve plexuses that are located on the sides of the spinal cord.. Cervical plexus is formed from the branches of the spinal nerves 1–4 segments of the spinal cord. Nerve fibers depart from it, which are solely responsible for motor, sensory function, or are mixed in nature. The motor ones are responsible for the work of the diaphragm - the muscle that separates the chest and abdominal cavities, and the sensory ones end with receptors on the pleura formed by spinal nerves that arise from the first four lumbar segments of the spinal cord, as well as from the twelfth thoracic segment. On the right and left, the plexus is located on the transverse processes of the lumbar vertebrae and is covered by the massive muscles of the lumbar group. It is very important what exactly The urinary bladder is innervated from the lumbar plexus and, accordingly, the act of urination. It happens consciously. Sacral plexus formed by the first four pairs of spinal nerves arising from the sacral segments of the spinal cord, as well as by the spinal nerves of the fifth and partly fourth lumbar segment of the spinal cord..The plexus contains nerve fibers that are motor, sensory, and autonomic in nature. They innervate the skin, bones and muscles of the lower extremities Coccygeal plexus

is the smallest in the body. It is formed by the trunks of the spinal nerves, which arise from the last sacral segment of the spine and the first coccygeal segment.

These nerves innervate the coccygeus muscle and also send nerve receptors to the skin around the anus.
The structure of the spinal cord and brain. The nervous system is divided into central, located in the skull and spine, and peripheral, outside the skull and spine. The central nervous system consists of the spinal cord and the brain.

Rice. 105. Nervous system (diagram):

The spinal cord consists of two symmetrical halves connected by a narrow bridge, or commissure. A cross-section of the spinal cord shows that in the middle there is a gray matter consisting of neurons and their processes, in which two large, wide anterior horns and two narrower posterior horns are distinguished. In the thoracic and lumbar segments there are also lateral projections - lateral horns. In the anterior horns there are motor neurons, from which centrifugal nerve fibers depart, forming the anterior, or motor, roots, and through the dorsal roots, centripetal nerve fibers of the neurons of the spinal ganglia enter the dorsal horns. The gray matter also contains blood vessels. There are 3 main groups of neurons in the spinal cord: 1) large motor neurons with long, low-branching axons, 2) forming the intermediate zone of gray matter; their axons are divided into 2-3 long branches, and 3) sensitive, part of the spinal ganglia, with highly branching axons and dendrites.

The gray matter is surrounded by white matter, which consists of longitudinally located pulpal and partly non-pulphate nerve fibers, neuroglia and blood vessels. In each half of the spinal cord, the white matter is divided into three columns by the horns of gray matter. The white matter located between the anterior groove and the anterior horn is called the anterior columns, between the anterior and posterior horn - the lateral columns, between the posterior bridge and the posterior horn - the posterior columns. Each column consists of individual bundles of nerve fibers. In addition to the thick pulpy fibers of the motor neurons, thin nerve fibers of the lateral horn neurons belonging to the autonomic nervous system emerge along the anterior roots. In the dorsal horns there are intercalary, or fascicle, neurons, the nerve fibers of which connect motor neurons of different segments and are part of the white matter bundles. Pulmonary nerve fibers are divided into short - local pathways of the spinal cord, and long - long pathways connecting the spinal cord to the brain.

Rice. 106. Cross section of the spinal cord. Diagram of pathways. On the left are the ascending paths, on the right are the descending paths. Ascending paths:
/ - delicate bun; XI - wedge-shaped bundle; X - posterior spinocerebellar tract; VIII - anterior spinocerebellar tract; IX, VI - lateral and anterior spinothalamic tracts; XII - spinotectal tract.
Descending paths:
II, V - lateral and anterior pyramidal tracts; III - rubrospinal tract; IV - vestibulo-spinal tract; VII - olivospinal tract.
Circles (without numbering) indicate pathways connecting segments of the spinal cord.

The ratio of gray and white matter in different segments of the spinal cord is not the same. The lumbar and sacral segments contain, due to a significant decrease in the content of nerve fibers in the descending tracts and the beginning of the formation of the ascending tracts, more gray matter than white matter. In the middle and especially upper thoracic segments there is relatively more white matter than gray matter.

In the cervical segments, the amount of gray matter increases and white matter increases significantly. Thickening of the spinal cord in the cervical region depends on the development of innervation of the arm muscles, and thickening of the lumbar region depends on the development of innervation of the leg muscles. Consequently, the development of the spinal cord is determined by the activity of skeletal muscles.

The supporting basis of the spinal cord is neuroglia and the connective tissue layer of the pia mater penetrating into the white matter. The surface of the spinal cord is covered with a thin neuroglial membrane, which contains blood vessels. Outside the soft tissue there is an arachnoid membrane connected to it, made of loose connective tissue, in which cerebrospinal fluid circulates. The arachnoid membrane adheres tightly to the outer hard shell of dense connective tissue with a large number of elastic fibers.

Rice. 107. Layout of spinal cord segments. The location of the spinal cord segments in relation to the corresponding vertebrae and the places where the roots exit the spinal canal are shown.

The human spinal cord consists of 31-33 segments, or segments: cervical - 8, thoracic - 12, lumbar - 5, sacral - 5, coccygeal - 1-3. Two pairs of roots emerge from each segment, connecting into two spinal nerves, consisting of centripetal - sensory and centrifugal - motor nerve fibers. Each nerve begins at a certain segment of the spinal cord with two roots: anterior and posterior, which end at the spinal ganglion and, joining together outward from the node, form a mixed nerve. Mixed spinal nerves exit the spinal canal through the intervertebral foramina, except for the first pair, passing between the edge of the occipital bone and the upper edge of the 1st cervical vertebra, and the coccygeal root, between the edges of the vertebrae of the coccyx. The spinal cord is shorter than the spine, so there is no correspondence between the spinal cord segments and the vertebrae.

Spinal nerves innervate the skin and muscles of the trunk, arms and legs. They form: 1) the cervical plexus, consisting of 4 upper cervical nerves, innervating the skin of the neck, back of the head, auricle and skin on the collarbone, neck muscles and diaphragm; 2) brachial plexus of 4 lower cervical nerves and 1st thoracic nerve, innervating the skin and muscles of the shoulder girdle and arm; 3) thoracic nerves, which correspond to the 12 thoracic segments of the spinal cord and innervate the skin and muscles of the chest and abdomen (anterior branch) and the skin and muscles of the back (posterior branch), therefore, the thoracic spinal nerves have the correct segmental location and are clearly divided into anterior - abdominal part and back - dorsal part; 4) lumbar plexus, consisting of the 12th thoracic and 4 upper lumbar nerves, innervating the skin and part of the muscles of the pelvis, thigh, leg and foot; 5) sacral plexus, consisting of the lower lumbar, sacral and coccygeal nerves, innervating the skin and other muscles of the pelvis, thigh, leg and foot.

Rice. 108. Brain, median surface:
I - frontal lobe of the cerebrum, 2 - parietal lobe, 3 - occipital lobe, 4 - corpus callosum, 5 - cerebellum, 6 - optic thalamus (diencephalon), 7 - pituitary gland, 8 - quadrigeminal (midbrain), 9 - pineal gland , 10 - pons, 11 - medulla oblongata

The brain also consists of gray and white matter. The gray matter of the brain is represented by a variety of neurons, grouped into numerous clusters - nuclei and covering different parts of the brain on top. In total, there are approximately 14 billion neurons in the human brain. In addition, the gray matter contains neuroglial cells, which are approximately 10 times more numerous than neurons; they make up 60-90% of the total brain mass. Neuroglia are scaffolding tissues that support neurons. It is also involved in the metabolism of the brain and especially neurons; hormones and hormone-like substances are formed in it (neurosecretion).

The brain is divided into the medulla oblongata and the pons, the cerebellum, midbrain and diencephalon, which make up its trunk, and the telencephalon, or cerebral hemispheres, covering the brain stem from above (Fig. 108). In humans, unlike animals, the volume and weight of the brain sharply predominate over the spinal cord: approximately 40-45 times or more (in chimpanzees, the weight of the brain exceeds the weight of the spinal cord only 15 times). The average weight of the adult human brain is approximately 1400 g in men and, due to the relatively lower average body weight, approximately 10% less in women. A person's mental development does not directly depend on the weight of his brain. Only in cases where the weight of a man’s brain is below 1000 g, and that of a woman is below 900 g, the structure of the brain is disrupted and mental abilities are reduced.

Rice. 109. Anterior surface of the brain stem. Origin of cranial nerves. Inferior surface of the cerebellum:
1 - optic nerve, 2 - insula, 3 - pituitary gland, 4 - optic chiasm, 5 - infundibulum, 6 - gray tubercle, 7 - mamillar body, 8 - fossa between the crura, 9 - cerebral peduncle, 10 - semilunar node, 11 - minor root of the trigeminal nerve, 12 - major root of the trigeminal nerve, 13 - abducens nerve, 14 - glossopharyngeal nerve, 15 - choroid plexus of the fourth ventricle, 16 - vagus nerve, 17 - accessory nerve, 18 - first cervical nerve, 19 - pyramidal chiasm , 20 - pyramid, 21 - hypoglossal nerve, 22 - auditory nerve, 23 - intermediate nerve, 24 - facial nerve, 25 - trigeminal nerve, 26 - pons, 27 - trochlear nerve, 28 - external geniculate body, 29 - oculomotor nerve , 30 - visual tract, 31-32 - anterior perforated substance, 33 - external olfactory stripe, 34 - olfactory triangle, 35 - olfactory tract, 36 - olfactory bulb

12 pairs of cranial nerves emerge from the nuclei of the brain stem, which, unlike the spinal nerves, do not have a correct segmental exit and a clear division into the abdominal and dorsal parts. Cranial nerves are divided into: 1) olfactory, 2) visual, 3) oculomotor, 4) trochlear, 5) trigeminal, 6) abducens, 7) facial, 8) auditory, 9) glossopharyngeal, 10) vagus, 11) accessory, 12 ) sublingual.

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The human spinal cord is the most important organ of the central nervous system, connecting all organs with the central nervous system and conducting reflexes. It is covered on top with three shells:

• hard, cobwebby and soft

Between the arachnoid and soft (vascular) membrane and in its central canal there is cerebrospinal fluid (liquor)

IN epidural space (the space between the dura mater and the surface of the spine) - vessels and adipose tissue

What is the external structure of the spinal cord?

This is a long cord in the spinal canal, in the form of a cylindrical cord, approximately 45 mm long, about 1 cm wide, flatter in front and behind than on the sides. It has a conditional upper and lower bound. The upper one begins between the line of the foramen magnum and the first cervical vertebra: in this place the spinal cord connects to the brain through the intermediate medulla. The lower one is at the level of 1-2 lumbar vertebrae, after which the cord takes on a conical shape and then “degenerates” into a thin spinal cord ( terminal) with a diameter of about 1 mm, which stretches to the second vertebra of the coccygeal region. The terminal filament consists of two parts - internal and external:

• internal - approximately 15 cm long, consists of nervous tissue, intertwined by the lumbar and sacral nerves and is located in a sac of dura mater
• outer - about 8 cm, begins below the 2nd vertebra of the sacral region and stretches in the form of a connection of the hard, arachnoid and soft membranes to the 2nd coccygeal vertebra and fuses with the periosteum

The outer terminal filament, hanging down to the coccyx, with the nerve fibers intertwining it, is very similar in appearance to a horse’s tail. Therefore, pain and phenomena that occur when nerves are pinched below the 2nd sacral vertebra are often called cauda equina syndrome.

The spinal cord has thickenings in the cervical and lumbosacral regions. This is explained by the presence of a large number of exiting nerves in these places, going to the upper as well as to the lower extremities:

1. Cervical thickening extends from the 3rd - 4th cervical vertebrae to the 2nd thoracic vertebrae, reaching a maximum in the 5th - 6th
2. Lumbosacral - from the level of the 9th - 10th thoracic vertebrae to the 1st lumbar with a maximum in the 12th thoracic

Gray and white matter of the spinal cord

If you look at the structure of the spinal cord in cross section, then in the center you can see a gray area in the form of a butterfly spreading its wings. This is the gray matter of the spinal cord. It is surrounded on the outside by a white substance. The cellular structure of gray and white matter differs from each other, as do their functions.

The gray matter of the spinal cord consists of motor and interneurons:

• motor neurons transmit motor reflexes
• intercalary - provide communication between the neurons themselves

White matter consists of so-called axons— nerve processes from which the fibers of the descending and ascending pathways are created.

The wings of the “butterfly” are narrower and form front horns gray matter, wider - rear. The anterior horns contain motor neurons, in the rear - insertion. Between the symmetrical side parts there is a transverse bridge made of brain tissue, in the center of which there is a canal that communicates at the top with the cerebral ventricle and is filled with cerebrospinal fluid. In some sections or even along its entire length in adults, the central canal may become overgrown.

Relative to this canal, to the left and right of it, the gray matter of the spinal cord looks like symmetrically shaped columns connected to each other by anterior and posterior commissures:

• the anterior and posterior columns correspond to the anterior and posterior horns in cross section
• lateral projections form a side pillar

The lateral projections are not present along their entire length, but only between the 8th cervical and 2nd lumbar segments. Therefore, the cross section in segments where there are no lateral protrusions has an oval or round shape.

The connection of symmetrical columns in the anterior and posterior parts forms two grooves on the surface of the brain: the anterior, deeper one, and the posterior. The anterior fissure ends in a septum adjacent to the posterior border of the gray matter.

Spinal nerves and segments

To the left and right of these central grooves are located respectively anterolateral And posterolateral grooves through which the anterior and posterior filaments emerge ( axons), forming nerve roots. The anterior root in its structure is motor neurons anterior horn. The posterior one, responsible for sensitivity, consists of interneurons posterior horn. Immediately at the exit from the medullary segment, both the anterior and posterior roots unite into one nerve or nerve ganglion ( ganglion). Since in total each segment has two anterior and two posterior roots, in total they form two spinal nerve(one on each side). Now it is not difficult to calculate how many nerves the human spinal cord has.

To do this, let us consider its segmental structure. There are 31 segments in total:

• 8 - in the cervical region
• 12 - in the chest
• 5 - lumbar
• 5 - in the sacrum
• 1 - in the coccygeal

This means that the spinal cord has only 62 nerves - 31 on each side.

The sections and segments of the spinal cord and spine are not at the same level due to the difference in length (the spinal cord is shorter than the spine). This must be taken into account when comparing the brain segment and vertebral number when performing radiology and tomography: if at the beginning of the cervical spine this level corresponds to the vertebral number, and in its lower part lies on the vertebra above, then in the sacral and coccygeal sections this difference is already several vertebrae.

Two important functions of the spinal cord

The spinal cord performs two important functions − reflex And conductor. Each of its segments is associated with specific organs, ensuring their functionality. For example:

• Cervical and thoracic region - connects with the head, arms, chest organs, chest muscles
• Lumbar region - gastrointestinal tract, kidneys, muscular system of the trunk
• Sacral region - pelvic organs, legs

Reflex functions are simple reflexes inherent in nature. For example:

• pain reaction - pull your hand away if it hurts.
• knee reflex

Reflexes can be carried out without the participation of the brain

This is proven by simple experiments on animals. Biologists conducted experiments with frogs, checking how they react to pain in the absence of a head: a reaction was noted to both weak and strong painful stimuli.

The conductor functions of the spinal cord consist of conducting an impulse along the ascending path to the brain, and from there along the descending path in the form of a return command to some organ

Thanks to this conductive connection, any mental action is carried out:
get up, go, take, throw, lift, run, cut, draw- and many others that a person, without noticing, does in his daily life at home and at work.

Such a unique connection between the central brain, the spinal cord, the entire central nervous system and all organs of the body and its limbs, as before, remains the dream of robotics. Not a single robot, even the most modern one, is yet capable of performing even a thousandth of those various movements and actions that are subject to the control of a biological organism. As a rule, such robots are programmed for highly specialized activities and are mainly used in automatic conveyor production.

Functions of gray and white matter. To understand how these magnificent functions of the spinal cord are carried out, consider the structure of the gray and white matter of the brain at the cellular level.

The gray matter of the spinal cord in the anterior horns contains large nerve cells called efferent(motor) and are combined into five nuclei:

• central
• anterolateral
• posterolateral
• anteromedial and posteromedial

The sensory roots of small cells of the dorsal horns are specific cell processes from the sensory ganglia of the spinal cord. In the dorsal horns, the structure of the gray matter is heterogeneous. Most of the cells form their own nuclei (central and thoracic). The border zone of the white matter, located near the posterior horns, is adjacent to the spongy and gelatinous zones of the gray matter, the cell processes of which, together with the processes of small diffusely scattered cells of the posterior horns, form synapses (contacts) with the neurons of the anterior horns and between adjacent segments. These neurites are called anterior, lateral and posterior bundles of their own. Their connection with the brain is carried out using white matter pathways. Along the edge of the horns, these tufts form a white border.

The lateral horns of gray matter perform the following important functions:

• In the intermediate zone of gray matter (lateral horns) there are sympathetic cells vegetative nervous system, it is through them that communication with internal organs is carried out. The processes of these cells connect to the anterior roots
• Here it is formed spinocerebellar path:
  At the level of the cervical and upper thoracic segments there is reticular zone - a bundle of a large number of nerves associated with zones of activation of the cerebral cortex and reflex activity.

The segmental activity of the gray matter of the brain, the posterior and anterior roots of the nerves, and the own bundles of white matter bordering the gray is called the reflex function of the spinal cord. The reflexes themselves are called unconditional, according to Academician Pavlov’s definition.

The conductive functions of white matter are carried out through three cords - its outer sections, limited by grooves:

• Anterior funiculus - the area between the anterior median and lateral grooves
• Posterior funiculus - between the posterior median and lateral grooves
• Lateral funiculus - between the anterolateral and posterolateral grooves

White matter axons form three conduction systems:

• short bundles called associative fibers that connect different segments of the spinal cord
• ascending sensitive (afferent) beams directed to parts of the brain
• descending motor (efferent) bundles directed from the brain to the neurons of the gray matter of the anterior horns

Ascending and descending conduction pathways. Let's look at some of the functions of the white matter cord pathways as an example:

Front ropes:

• Anterior pyramidal (corticospinal) tract- transmission of motor impulses from the cerebral cortex to the spinal cord (anterior horns)
• Spinothalamic anterior tract- transmission of tactile impulses affecting the surface of the skin (tactile sensitivity)
• Tectospinal tract- connecting the visual centers under the cerebral cortex with the nuclei of the anterior horns, creates a protective reflex caused by sound or visual stimuli
• Bundle of Held and Leventhal (vestibular tract)- white matter fibers connect the vestibular nuclei of eight pairs of cranial nerves with motor neurons of the anterior horns
• Longitudinal posterior beam- connecting the upper segments of the spinal cord with the brain stem, coordinating the work of the eye muscles with the cervical muscles, etc.

The ascending pathways of the lateral cords carry impulses of deep sensitivity (feelings of one’s body) along the corticospinal, spinothalamic and tegmental spinal tracts.

Descending tracts of the lateral funiculi:

• Lateral corticospinal (pyramidal)- transmits the impulse of movement from the cerebral cortex to the gray matter of the anterior horns
• Red nuclear spinal tract(located in front of the lateral pyramidal), the spinocerebellar posterior and spinothalamic lateral tracts are adjacent to it.
  The red nucleus spinal tract automatically controls movements and muscle tone at a subconscious level.

Different parts of the spinal cord have different proportions of gray and white brain matter. This is explained by the different number of ascending and descending paths. The lower spinal segments have more gray matter. As you move upward, it becomes less, and the white matter, on the contrary, increases, as new ascending pathways are added, and at the level of the upper cervical segments and the middle part of the chest there is the most white. But in the area of ​​both the cervical and lumbar thickenings, gray matter predominates.

As you can see, the spinal cord has a very complex structure. The connection between nerve bundles and fibers is vulnerable, and serious injury or illness can disrupt this structure and lead to disruption of the conduction pathways, which is why below the “break” point of conduction there can be complete paralysis and loss of sensitivity. Therefore, at the slightest dangerous sign, the spinal cord must be examined and treated promptly.

Spinal cord puncture

To diagnose infectious diseases (encephalitis, meningitis and other diseases), a spinal cord puncture (lumbar puncture) is used - inserting a needle into the spinal canal. It is carried out this way:
IN subarachnoid the space of the spinal cord at a level below the second lumbar vertebra is inserted with a needle and taken cerebrospinal fluid (cerebrospinal fluid).
This procedure is safe, since below the second vertebra in an adult there is no spinal cord, and therefore there is no threat of damage to it.

However, it requires special care so as not to introduce infection or epithelial cells under the membrane of the spinal cord.

Spinal cord puncture is performed not only for diagnosis, but also for treatment, in the following cases:

• injection of chemotherapy drugs or antibiotics under the lining of the brain
• for epidural anesthesia during operations
• for the treatment of hydrocephalus and reduction of intracranial pressure (removal of excess cerebrospinal fluid)

Spinal cord puncture has the following contraindications:

• spinal canal stenosis
• displacement (dislocation) of the brain
• dehydration (dehydration)

Take care of this important organ, engage in basic prevention:

1. Take antiviral medications during a viral meningitis epidemic
2. Try not to have picnics in the forested area in May-early June (the period when the encephalitis tick is active)

The part of the central nervous system that we will talk about today is located in the spinal canal and is a thick-walled tube, inside of which there is a narrow canal. We are talking about the spinal cord. It is slightly flattened in the anterior and posterior directions, and is quite complex in its structure. Along the spinal cord, impulses from the brain enter the peripheral structures of the nervous system. Plus, it performs its reflex functions. If the spinal cord did not function, a person would not be able to breathe normally. Urination, digestion, movement, sexual activity - all this would be impossible. Next, we will consider its role and functions in the body in more detail.

Features of the spinal cord

The formation of the part of the nervous system in question occurs in the fourth week of the child’s development inside the womb. Throughout pregnancy, sections of the spinal cord are formed, and some of them are completely formed in the first two years after the birth of the baby. The spinal cord conventionally begins in the area
the upper edge of the first cervical vertebra, as well as the foramen magnum of the skull. Here it undergoes a smooth restructuring into the spinal cord, but there is no clear division. At this point, the pyramidal tracts of the vertebrae intersect, which allow the arms and legs to move.

As for the lower edge of the spinal cord, it is at the level of the upper part of the second lumbar vertebra, that is, the length of the spinal cord is smaller than the spine. For this reason, it is possible to perform a spinal puncture at the level of the III - IV lumbar vertebrae without damaging the spinal cord, because it simply is not there. If we consider it from such a parameter as size, it turns out that it is approximately 40-45 cm in length, 1-1.5 cm in width and weighs 30-35 g. Along the length, the component of the central nervous system in question is divided into such sections as the cervical and thoracic . There is also the lumbar, sacral and coccygeal (here the brain is thicker, since there are nerve cells responsible for the motor capabilities of the limbs).

The final sacral segments and one coccygeal segment are called the “conus of the spinal cord”, since the shape resembles this particular figure. The cone passes into the terminal filament, which has no nerves, is covered with membranes of the spinal cord and consists of connective tissue. The thread is fixed on the II coccygeal vertebra. It is worth adding that the entire length of the brain is covered with three membranes. The internal one (also known as the first or soft one) protects the venous and arterial vessels that supply the spinal cord with blood. Next comes the arachnoid, middle or arachnoid membrane. Between the first and second membranes there is a space filled with cerebrospinal fluid (CSF), designated as subarachnoid (subarachnoid).

It is from there that during puncture the cerebrospinal fluid is taken for study. Finally, there is the dura mater or outer shell, which extends to the foramina between the vertebrae. By the way, ligaments allow the spinal cord to be fixed inside the spinal canal. Experts also note that along the entire length of the spinal cord in its center there is a central canal with cerebrospinal fluid.

Grooves with slits protrude into the spinal cord, or more precisely, into its depths on all sides. The anterior and posterior median fissures that separate the spinal cord into halves are considered large. In these halves there are grooves that split the brain into cords - several anterior, as many posterior and lateral. The nerve fibers in the cords are different, that is, some report touch, others report pain, etc.

Spinal cord and its segments

The described part of the central nervous system has divisions. A pair of anterior and posterior roots emerge from each. They are associated with the nervous system and organs. The roots, leaving the spinal canal, create nerves and they are sent to the necessary structures of the body. Anterior (or motor) are mainly related to the transmission of information about movements, that is, they are stimulators of muscle contraction. The posterior (or sensory) ones send signals about sensations.

Experts add that each person has 8 cervical segments. There are also 12 thoracic, 5 lumbar and the same number of sacral. Plus, there are 1-3 coccygeal sections (one is more common). Since the spinal cord is shorter in length than the spinal canal, the roots have to change direction. In particular, in the cervical region they are oriented horizontally. In the thoracic direction it is oblique, but in the lumbosacral direction it is almost vertical (here the roots are the longest).

Spinal cord and neurons

Gray and white colors are visible on the cut. The first represents the bodies of neurons, and the second represents the processes of the bodies of neurons (peripheral and central). In total, the spinal cord contains approximately 13 million nerve cells. The bodies of neurons, when positioned, create a shape similar to a butterfly, in which one can trace the convexities, that is, horns. The front ones are thick and massive, the rear ones are the opposite. The anterior horns contain neurons associated with motor abilities, and the posterior horns contain neurons associated with sensory abilities. There are also lateral horns with neurons of the autonomic nervous system.

In addition, nerve cells (more precisely, bodies) responsible for the functioning of certain organs are concentrated in parts of the spinal cord. It is known that in the 8th cervical and 1st thoracic segments, neurons innervate the pupil. Impulses are transmitted to the diaphragm through the 3rd and 4th cervical segments. And the thoracic regions and the nerves in them regulate the functioning of the heart. The lateral horns of the 2-5th sacral segments regulate the functions of the bladder and rectum. These data are very important for diagnosis.

At the same time, the upward and downward processes of the neuron bodies are connected with each other, the spinal cord and the brain. We are talking about the white substance that forms the cords. It is interesting that in the latter, the distribution of fibers follows a certain pattern, that is, the posterior cords contain conductors from muscles and joints, from the skin (tactile perception). In the lateral cords, fibers are also associated with touch, as well as with the perception of temperature and pain - from here the information enters the brain. Plus, the cerebellum is involved, thus understanding the position of the body. The lateral cords also provide movements that are programmed in the brain. Finally, the anterior cords transmit motor information via descending pathways, and sensory information via ascending pathways.

Blood supply to the spinal cord

Vessels supplying the spinal cord depart from the aorta and spinal arteries. Nutrients are supplied to the upper segments with blood through the anterior and posterior spinal arteries. Throughout the entire length of the spinal cord, the radicular spinal arteries flow into these arteries (carry blood from the aorta). As a rule, there are 6-8 anterior ones, but individual characteristics play a role here, but the lower radicular-spinal one is considered the largest and is called the “Adamkiewicz artery”.

Some people have an accessory artery of Deproge-Gotteron (coming from the sacral arteries). It is noteworthy that there are 15-20 posterior radicular-spinal arteries - this is more than the anterior ones, but they are smaller in diameter. In the nutrition of the spinal cord, the junctions of blood vessels, that is, anastomoses, are important. Thanks to them, in case of problems with a certain vessel (for example, a blood clot blocks it), the blood flow moves precisely through these same anastomoses.

There is also a venous system in the spinal cord - it is connected to the veins of the skull. Experts note that blood flows from the spinal cord through a chain system into the vena cava (superior and inferior). To prevent blood from flowing in the opposite direction, there are valves in the meninges.

Reflex activity of the spinal cord

If there is an irritating effect on the nervous system, a reflex occurs. For example, if you touch a hot kettle, your skin receptors will perceive the temperature. Next, the corresponding impulse is sent along the peripheral nerve fiber to the spinal cord. In the spinal ganglion at the intervertebral foramen there is a neuron body. From here, the signal travels along the central fiber to the dorsal horns of the spinal cord. Here there is a kind of switching to a new neuron, the processes of which rush to the anterior horns

Here the impulse passes to motor neurons. The processes of the latter emerge from the spinal cord through the hole between the vertebrae in order to move as part of the nerve to the muscles of the arm, muscle contraction occurs and the arm withdraws. This whole process is a reflex arc or ring that provides a response if there is a stimulus. The example shows that the brain was not involved. Simply put, we are dealing with reflexes. Those, by the way, can be congenital and acquired during life. And when checking your health, a specialist can check superficial and deep reflexes.

The first, for example, can be considered plantar, when drawing the skin of the foot in the form of a stroke from the heel upward provokes the flexion of the toes. There is also a second group - these are the flexion-elbow, knee, carporadial, Achilles and other reflexes.

Conducting task of the spinal cord

As you might guess, the spinal cord, in addition to the above-described function, carries out the transmission of signals from the skin, mucous organs to the brain and vice versa. This is where the white matter is involved. The paths for transmitting impulses, as described earlier, are descending and ascending. If the connection between the spinal cord and the brain is in order, there are no injuries, etc., the brain receives signals about body position, touch, muscle tension, pain, etc. (the ascending path is used for this). But along the descending path, the brain can control the body, say, if you need to catch up with a bus, the brain signals the spinal cord and the necessary muscles come into action.