The membranes of the brain and spinal cord come in only a few types. Modern medicine distinguishes hard, arachnoid and soft structures. Their main task is to protect the brain from stress, concussions, injuries, microtraumas and other factors that can negatively affect the functioning of the nervous system, and to nourish the brain with useful elements. Without them, the cerebrospinal fluid alone would not be able to fully cope with the shock-absorbing function.

Structural features

The spinal cord and brain are a single whole, an integral part of the nervous system. All mental functions, control of vital processes (activity, touch, sensitivity of the limbs) are carried out with their help. They are covered with protective structures that work harmoniously to provide nutrition and remove metabolic products.

The membranes of the spinal cord and brain are largely similar in structure. They continue the spine and envelop the spinal cord, preventing damage to it. This is a kind of “clothing” of the most important human organ, characterized by increased sensitivity. All layers are interconnected and they function as one, although their tasks are slightly different. There are three shells in total, and each has its own characteristics.

Dura shell

It is a fibrous formation with increased density, consisting of connective tissue. In the spine, it envelops the brain along with nerves and roots, spinal ganglia, as well as other membranes and fluid. The outer part is separated from the bone tissue by the epidural space, which consists of venous bundles and a fatty layer.

The hard shell of the spinal cord is inextricably linked with the same structure of the brain. In the head, the latter is fused with the periosteum, therefore it fits tightly to the inner surface of the skull, without forming an epidural space, which is its characteristic feature. The space between the dura mater and the arachnoid membrane is called the subdural; it is very narrow and filled with fluid similar to tissue.

The main functions of the hard shell are to create natural shock absorption, which reduces pressure and eliminates mechanical impact on the brain structure during movement or injury. In addition, there are a number of other tasks:

• synthesis of thrombin and fibrin - important hormones in the body;
• ensuring normal metabolic processes in tissues and lymph movement;
• normalization of blood pressure in the body;
• suppression of inflammatory processes;
• immunomodulation.

In addition, the shell has such an anatomy that it takes part in the blood supply. Tight closure with the vertebral bones allows it to reliably fix soft tissues in the ridge. This is important to ensure their safety during movement, physical exercise, falling, or injury.

Important! Connective tissue is attached to the periosteum by several types of ligaments: anterior, lateral, dorsal. If it is necessary to remove the dura mater, they present a serious obstacle for the surgeon due to the peculiarities of their structure.

Arachnoid

The arachnoid membrane of the human spinal cord is located on the outer part of the soft tissue, but deeper than the hard tissue. It covers the structure of the central nervous system and is devoid of color and blood vessels. In general, it is a connective tissue covered by endothelial cells. Connecting with the hard shell, it forms a space where the cerebrospinal fluid functions, but does not enter the grooves or depressions, passes by them, forming something like bridges. It is this cerebrospinal fluid that protects the nerve structures from various adverse effects and maintains water balance in the system.

Its main functions are:

• formation of hormones in the body;
• maintaining natural metabolic processes;
• transportation of cerebrospinal fluid into the venous blood;
• mechanical protection of the brain;
• formation of nervous tissue (in particular, cerebrospinal fluid);
• generation of nerve impulses;
• participation in metabolic processes in neurons.

The middle shell has a complex structure and looks like a mesh fabric, with a small thickness but high strength. It was its resemblance to a spider's web that gave it its name. Some experts believe that it is devoid of nerve endings, but this is only a theory that has not been proven to date.

Visual structure and location of the spinal cord membranes

Soft shell

Closest to the brain is the soft shell, which has a loose structure and consists of connective tissue. It contains blood vessels and plexuses, nerve endings and small arteries, all of which are responsible for providing the brain with enough blood for normal functioning. Unlike the arachnoid, it goes into all the cracks and grooves.

But, despite their close location, the brain is not covered by it, since between them there is a small space called subpial. It is separated from the subarachnoid space by many blood vessels. Its main functions include supplying the brain with blood and nutrients, normalizing metabolism and metabolism, as well as maintaining the natural performance of the body.

The functioning of all membranes is interconnected and the structure of the spine as a whole. Various malfunctions, changes in the amount of cerebrospinal fluid or inflammatory processes at any level lead to serious consequences and disorders and diseases of internal organs.

Spaces between shells

All the membranes of the spinal cord and brain, although they are close to each other, do not touch tightly. Spaces are formed between them, which have their own characteristics and functions.

• Epidural. It is located between the hard shell and the bone tissue of the spinal column. It is filled predominantly with fat cells to eliminate nutritional deficiencies. Cells become a strategic reserve for neurons in extreme situations, which ensures the control and functioning of processes in the body. This space reduces the load on the deep layers of the spinal cord, eliminating their deformation, due to its loose structure.
• Subdural. Located between the dura mater and the arachnoid membrane. It contains liquor, the amount of which always changes. On average, an adult has 150–250 ml. Cerebrospinal fluid provides the brain with nutrients (minerals, proteins), protects it from falls or impacts, maintaining pressure. Thanks to the movement of cerebrospinal fluid and its constituent lymphocytes and leukocytes, infectious processes are suppressed in the central nervous system and bacteria and microorganisms are absorbed.
• Subarachnoid. Located between the arachnoid and soft membrane. It constantly contains most of the cerebrospinal fluid. This allows you to most effectively protect the central nervous system, brainstem, cerebellum and medulla oblongata.

In case of tissue damage, the first step is to analyze the cerebrospinal fluid, as it allows you to determine the extent of the pathological process, predict the course, and choose effective control tactics. An infection or inflammation that appears in one area quickly spreads to neighboring ones. This is due to the constant movement of cerebrospinal fluid.

Diseases

The meninges can be injured or suffer from damage of an infectious nature. Increasingly, problems are associated with the development of oncology. They are recorded in patients of different ages and health conditions. In addition to infectious processes, there are other malfunctions:

• Fibrosis. It represents a negative consequence of the surgical intervention. It leads to an increase in the volume of the membrane, characteristic tissue scarring, and an inflammatory process that occurs immediately in all intershell spaces. The disease is also often provoked by cancer or spinal injuries.
• Meningitis. Severe pathology of the spinal cord, which occurs as a result of the penetration of a viral infection into the body (pneumococcus, meningococcus). It is accompanied by a number of characteristic symptoms and, if left untreated, can lead to serious complications and even death of the patient.
• Arachnoiditis. An inflammatory process develops in the lumbar region of the spinal cord, which also affects the membranes. All three levels suffer. Clinically, the disease manifests itself with focal symptoms and neurasthenic disorders.

The shells or the space between them can also be damaged as a result of injury. Usually these are bruises or fractures that cause compression of the spinal cord. Acute disruption of cerebrospinal fluid circulation causes paralysis or hydrocephalus. Many malfunctions of the membranes in the clinical picture can be confused with other infectious diseases, therefore an MRI is always prescribed to clarify the diagnosis.

Features of treatment

Inflammatory processes in the membranes of the spinal cord or brain require immediate treatment in a hospital setting. Self-medication of any disease at home often leads to death or serious complications. Therefore, when the first signs of illness appear, you should consult a doctor and follow all recommendations.

Features of treatment of possible pathologies:

• Viral infection. Monitor body temperature and take enough fluids. If a person cannot drink a lot of water, droppers with saline solution are prescribed. If cysts form or the volume of cerebrospinal fluid increases, then medications are required to normalize the pressure. The chosen tactics to combat inflammation are adjusted as the patient’s condition improves.
• Injury. The membranes of the spinal cord provide its normal nutrition and blood circulation, therefore, when scars, adhesions and other damage form, this function is disrupted, the movement of cerebrospinal fluid is hampered, which leads to the appearance of cysts and intervertebral hernia. Treatment in this case includes taking a set of medications to improve metabolic processes. If traditional therapy is ineffective, surgical intervention is prescribed.
• Infectious processes. The entry of pathogenic bacteria into the organ requires the prescription of antibiotics. In most cases, this is a broad-spectrum drug. An important point is also monitoring water balance and body temperature.

The consequences of diseases of the membranes can be unpredictable. Inflammatory processes cause disturbances in the functioning of the body, fever, vomiting, seizures, and convulsions. Often hemorrhages lead to paralysis, which makes a person disabled for life.

The spinal membranes form a single system and are directly connected to the hypothalamus and cerebellum. Violation of their integrity or inflammatory processes lead to a deterioration in the general condition. Usually accompanied by seizures, vomiting, and fever. Modern medicine has reduced the mortality rate due to such diseases to 10–15%. But the risk still exists. Therefore, when you notice the first signs, you should immediately consult a doctor.

The spinal cord and brain are covered by three membranes:

External - hard shell (dura mater);

Middle shell - arachnoid (arachnoidea);

- inner shell - soft (pia mater).

The membranes of the spinal cord in the area of ​​the foramen magnum continue into the membranes of the same name in the brain.

Directly to the outer surface of the brain, spinal and head, adjacent soft (choroidal) membrane, which goes into all the cracks and furrows. The soft shell is very thin, formed by loose connective tissue rich in elastic fibers and blood vessels. Connective tissue fibers depart from it, which, together with blood vessels, penetrate into the substance of the brain.

Located outside the choroid arachnoid . Between the soft shell and the arachnoid membrane, there is subarachnoid (subarachnoid) space, filled with cerebrospinal fluid -120-140 ml. In the lower part of the spinal canal, in the subarachnoid space, the roots of the lower (sacral) spinal nerves float freely and form the so-called "pony tail" In the cranial cavity above large fissures and grooves, the subarachnoid space is wide and forms receptacles - tanks.

The largest tanks are cerebellar-cerebral, lying between the cerebellum and medulla oblongata, lateral fossa cistern- located in the area of ​​the groove of the same name, optic chiasm tank located anterior to the optic chiasm, interpeduncular cistern located between the peduncles of the brain. The subarachnoid spaces of the brain and spinal cord communicate with each other at the junction of the spinal cord and the brain.

Flows into the subarachnoid space cerebrospinal fluid, formed in the ventricles of the brain. In the lateral, third and fourth ventricles of the brain there are choroid plexus, forming liquor. They consist of loose fibrous connective tissue with a large number of blood capillaries.

From the lateral ventricles, through the interventricular foramina, fluid flows into the third ventricle, from the third through the cerebral aqueduct into the fourth, and from the fourth through three openings (lateral and median) into the cerebellar-cerebral cistern of the subarachnoid space. The outflow of cerebrospinal fluid from the subarachnoid space into the blood occurs through protrusions – granulation of the arachnoid membrane, penetrating into the lumen of the sinuses of the dura mater of the brain, as well as into the blood capillaries at the site of exit of the roots of the cranial and spinal nerves from the cranial cavity and from the spinal canal. Thanks to this mechanism, cerebrospinal fluid is constantly formed in the ventricles and is absorbed into the blood at the same speed.

Outside the arachnoid membrane is located dura mater , which is formed by dense fibrous connective tissue. In the spinal canal, the dura mater of the spinal cord is a long sac containing the spinal cord with spinal nerve roots, spinal ganglia, pia mater, arachnoid membrane, and cerebrospinal fluid. The outer surface of the dura mater of the spinal cord is separated from the periosteum lining the spinal canal from the inside epidural space, filled with fatty tissue and venous plexus. The dura mater of the spinal cord at the top passes into the dura mater of the brain.

The dura mater of the brain fuses with the periosteum, so it directly covers the inner surface of the bones of the skull. Between the dura mater and the arachnoid membrane there is a narrow subdural space, which contains a small amount of liquid.

In some areas, the dura mater of the brain forms processes that consist of two sheets and are deeply invaginated into the cracks that separate parts of the brain from each other. In the places where the processes originate, the leaves split, forming triangular-shaped channels - sinuses of the dura mater. Venous blood flows into the sinuses from the brain through the veins, which then enters the internal jugular veins.

The largest process of the dura mater is falx cerebri. The falx separates the cerebral hemispheres from each other. At the base of the falx cerebri there is a splitting of its leaves - superior sagittal sinus. In the thickness of the free lower edge of the sickle there is inferior sagittal sinus.

Another large shoot - tentorium cerebellum separates the occipital lobes of the hemispheres from the cerebellum. The tentorium cerebellum is attached anteriorly to the upper edges of the temporal bones, and posteriorly to the occipital bone. Along the line of attachment to the occipital bone of the tentorium of the cerebellum, between its leaves a transverse sinus, which continues on the sides into a steam room sigmoid sinus. On each side, the sigmoid sinus passes into the internal jugular vein.

Between the cerebellar hemispheres there is falx cerebellum, attaching posteriorly to the internal nuchal crest. Along the line of attachment to the occipital bone of the falx of the cerebellum in its split there is occipital sinus.

Above the pituitary gland, the hard shell forms diaphragm of the sella turcica, which separates the pituitary fossa from the cranial cavity.

On the sides of the sella turcica there is cavernous sinus. The internal carotid artery passes through this sinus, as well as the oculomotor, trochlear and abducens cranial nerves and the ophthalmic branch of the trigeminal nerve.

Both cavernous sinuses are connected to each other transverse intercavernous sinuses. Doubles upper And inferior petrosal sinuses, lying along the edges of the pyramid of the temporal bone of the same name, they connect in front with the corresponding cavernous sinus, and behind and laterally with transverse and sigmoid sinuses.

On each side, the sigmoid sinus passes into the internal jugular vein.

Cerebrospinal fluid (CSF)

A biological fluid necessary for the proper functioning of brain tissue.
Physiological significance of cerebrospinal fluid:
1.mechanical protection of the brain;
2. excretory, i.e. removes metabolic products of nerve cells;
3. transport, transports various substances, including oxygen, hormones and other biologically active substances;
4.stabilization of brain tissue: maintains a certain concentration of cations, anions and pH, which ensures normal excitability of neurons;
5.performs the function of a specific protective immunobiological barrier.

Physico-chemical properties of liquor
Relative density. The normal specific gravity of cerebrospinal fluid is

1,004 – 1,006. An increase in this indicator is observed with meningitis, uremia, diabetes mellitus, etc., and a decrease is observed with hydrocephalus.
Transparency. Normally, cerebrospinal fluid is colorless and transparent, like distilled water. Cloudiness of the cerebrospinal fluid depends on a significant increase in the number of cellular elements (erythrocytes, leukocytes, tissue cellular elements), bacteria, fungi and an increase in protein content.
Fibrin (fibrinous) film. Normally, the cerebrospinal fluid contains virtually no fibrinogen. Its appearance in the cerebrospinal fluid is caused by diseases of the central nervous system that cause disruption of the blood-brain barrier. The formation of a fibrinous film is observed in purulent and serous meningitis, tumors of the central nervous system, cerebral hemorrhage, etc.
Color. Normally, cerebrospinal fluid is colorless. The appearance of color usually indicates a pathological process in the central nervous system. However, a grayish or grayish-pink color of the cerebrospinal fluid may be due to an unsuccessful puncture or subarachnoid hemorrhage.
Erythrocytarchy. Normally, red blood cells are not detected in the cerebrospinal fluid.
The presence of blood in the cerebrospinal fluid can be detected macro- and microscopically. There are traveling erythrocyterchia (artifact) and true erythrocytarchia.
Pathway erythrocytarchy caused by blood entering the cerebrospinal fluid when injured during puncture of blood vessels.
True erythrocytarchy occurs when hemorrhages into the cerebrospinal fluid spaces due to rupture of blood vessels during hemorrhagic stroke, brain tumors, and traumatic brain injuries.
Bilirubinarchia (xanthochromia)– the presence of bilirubin and other blood breakdown products in the cerebrospinal fluid.
Normally, bilirubin is not detected in the cerebrospinal fluid.
There are:
1.Hemorrhagic bilirubinarchy, caused by blood entering the cerebrospinal fluid spaces, the breakdown of which leads to the coloring of the cerebrospinal fluid in pink, and then in orange, yellow.
Observed in: hemorrhagic stroke, traumatic brain injury, rupture of a cerebral aneurysm.
Determination of blood and bilirubin in the cerebrospinal fluid allows one to diagnose the time of occurrence of bleeding into the cerebrospinal fluid spaces, its cessation and the gradual release of cerebrospinal fluid from blood breakdown products.
2.Congestive bilirubinarchy- this is the result of slow blood flow in the vessels of the brain, when, due to increased permeability of the vessel walls, blood plasma enters the cerebrospinal fluid.
This is observed with: tumors of the central nervous system, meningitis, arachnoiditis.
pH. This is one of the relatively stable indicators of cerebrospinal fluid.
Normally, the pH of the cerebrospinal fluid is 7.4 – 7.6.
Changes in pH in the cerebrospinal fluid affect cerebral circulation and consciousness.
Primary acidosis of the cerebrospinal fluid manifests itself in diseases of the nervous system: severe cerebral hemorrhages, traumatic brain injuries, cerebral infarction, purulent meningitis, status epilepticus, brain metastases, etc.
PROTEINARCHY(total protein) – the presence of protein in the cerebrospinal fluid.
Normally, the protein content in the cerebrospinal fluid is 0.15 – 0.35 g/l.
Hyperproteinarchy - an increase in protein content in the cerebrospinal fluid, serves as an indicator of the pathological process. Observed with: inflammation, tumors, brain injuries, subarachnoid bleeding.
GLYCOARCHY– presence of glucose in the liquor.
Normally, the glucose level in the cerebrospinal fluid is: 4.10 – 4.17 mmol/l.
The level of glucose in the cerebrospinal fluid is one of the most important indicators of the function of the blood-brain barrier.
Hypoglycoarchia is a decrease in glucose levels in the cerebrospinal fluid. Observed in: bacterial and fungal meningitis, tumors of the meninges.
Hyperglycoarchia - an increase in the level of glucose in the cerebrospinal fluid, is rare. Observed in: hyperglycemia, brain injury.
Microscopic examination of cerebrospinal fluid.
A cytological examination of the cerebrospinal fluid is performed to determine cytosis – the total number of cellular elements in 1 μl of cerebrospinal fluid with subsequent differentiation of cellular elements (cerebrospinal fluid formula).
Normally, there are practically no cellular elements in the cerebrospinal fluid: the cell content is allowed 0 – 8 * 10 6 /l.
Increase in the number of cells ( pleocytosis ) in the cerebrospinal fluid is considered a sign of damage to the central nervous system.
After counting the total number of cells, cell differentiation is carried out. The following cells may be present in the cerebrospinal fluid:
Lymphocytes. Their number increases with tumors of the central nervous system. Lymphocytes are found in chronic inflammatory processes in the membranes (tuberculous meningitis, cysticercosis arachnoiditis).
Plasma cells. Plasma cells are found only in pathological cases with long-term inflammatory processes in the brain and membranes, with encephalitis, tuberculous meningitis, cysticercosis arachnoiditis and other diseases, in the postoperative period, with sluggish wound healing.
Tissue monocytes. They are discovered after surgery on the central nervous system, with long-term inflammatory processes in the membranes. The presence of tissue monocytes indicates an active tissue reaction and normal wound healing.
Macrophages. Macrophages are not found in normal cerebrospinal fluid. The presence of macrophages with normal cytosis is observed after bleeding or during an inflammatory process. As a rule, they occur in the postoperative period.

Neutrophils. The presence of neutrophils in the cerebrospinal fluid, even in minimal quantities, indicates either a former or existing inflammatory reaction.

Eosinophils found in subarachnoid hemorrhages, meningitis, tuberculous and syphilitic brain tumors.
Epithelial cells. Epithelial cells delimiting the subarachnoid space are rare. They are found during neoplasms, sometimes during inflammatory processes.

Arachnoidea, arachnoidea , thin, transparent, devoid of blood vessels and consists of connective tissue covered with endothelium. It encircles the spinal cord and brain on all sides and is connected to the soft shell lying medially by means of numerous arachnoid trabeculae, and in some places fuses with it.

Arachnoid membrane of the spinal cord

Rice. 960. Arachnoid membrane of the spinal cord (photo. Specimen by V. Kharitonova). (Area of ​​a completely stained specimen. Trabeculae of the subarachnoid space.)

Arachnoidea mater spinalis (Fig.; see Fig.,), like the dura mater of the spinal cord, is a sac that relatively freely surrounds the spinal cord.

Between the arachnoid and pia mater of the spinal cord is subarachnoid space, cavitas subarachnoidea, - a more or less extensive cavity, especially in the anterior and posterior sections, reaching 1–2 mm in the transverse direction and made cerebrospinal fluid, liquor cerebrospinalis.

The arachnoid membrane of the spinal cord is connected to the dura mater of the spinal cord in the region of the spinal nerve roots, in those places where these roots penetrate the dura mater of the spinal cord (see earlier). It is connected to the soft membrane of the spinal cord through numerous, especially in the posterior sections, arachnoid trabeculae, which form the posterior subarachnoid septum.

In addition, the arachnoid membrane of the spinal cord is connected to both the hard and soft membranes of the spinal cord using special dentate ligaments, ligamenta denticulata. They are connective tissue plates (20–25 in total), located in the frontal plane on both lateral sides of the spinal cord and extending from the soft shell to the inner surface of the hard shell.

Arachnoid membrane of the brain

Arachnoidea mater encephali (Fig. , ), covered, like the spinal cord shell of the same name, with endothelium, is connected to the soft shell of the brain by subarachnoid trabeculae, and to the hard shell by granulations of the arachnoid membrane. Between it and the dura mater of the brain there is a slit-like subdural space filled with a small amount of cerebrospinal fluid.

The outer surface of the arachnoid membrane of the brain is not fused with the adjacent dura mater. However, in places, mainly on the sides of the superior sagittal sinus and to a lesser extent on the sides of the transverse sinus, as well as near other sinuses, its processes of varying sizes - the so-called granulations of the arachnoid membrane, granulationes arachnoideales, enter the dura mater of the brain and, together with it, into the inner surface of the cranial bones or sinuses. In these places, small depressions are formed in the bones, the so-called granulation dimples; there are especially many of them near the sagittal suture of the cranial vault. Granulations of the arachnoid membrane are organs that filter the outflow of cerebrospinal fluid into the venous bed.

The inner surface of the arachnoid membrane faces the brain. On the prominent parts of the convolutions of the brain, it is closely adjacent to the pia mater of the brain, without, however, following the latter into the depths of the grooves and fissures. Thus, the arachnoid membrane of the brain spreads like bridges from gyrus to gyrus, and in places where there are no adhesions, spaces remain, called subarachnoid spaces, cavitates subarachnoideale.

The subarachnoid spaces of the entire surface of the brain, as well as the spinal cord, communicate with each other. In some places these spaces are quite significant and are called subarachnoid cisterns, cisternae subarachnoideae(rice. , ). The largest tanks stand out:

1. cerebellomedullary cistern, cisterna cerebellomedullaris, lies between the cerebellum and medulla oblongata;
2. cistern of the lateral fossa of the cerebrum, cisterna fossae lateralis cerebri, – in the lateral sulcus, corresponding to the lateral fossa of the cerebrum;
3. interpeduncular cistern, cisterna interpeduncularis, – between the cerebral peduncles;
4. cross tank, cisterna chiasmatis, – between the optic chiasm and the frontal lobes of the brain.

In addition, there are a number of large subarachnoid spaces that can be classified as cisterns: running along the upper surface and knee of the corpus callosum cistern of the corpus callosum; located at the bottom of the transverse fissure of the cerebrum, between the occipital lobes of the hemispheres and the superior surface of the cerebellum, bypass tank, which looks like a canal running along the sides of the cerebral peduncles and the roof of the midbrain; bridge side tank, lying under the middle cerebellar peduncles, and, finally, in the region of the basilar sulcus of the bridge - middle bridge tank.

The subarachnoid cavities of the brain communicate with each other, as well as through the median and lateral apertures with the cavity of the fourth ventricle, and through the latter with the cavity of the remaining ventricles of the brain.

Gathers in the subarachnoid space cerebrospinal fluid, liquor cerebrospinalis, from different parts of the brain.

The outflow of fluid from here goes through the perivascular, perineural fissures and through the granulations of the arachnoid membrane into the lymphatic and venous pathways.

The spinal cord is covered on the outside with membranes that are a continuation of the membranes of the brain. They perform the functions of protection against mechanical damage, provide nutrition to neurons, control water metabolism and metabolism of nervous tissue. Cerebrospinal fluid, which is responsible for metabolism, circulates between the membranes.

The spinal cord and brain are parts of the central nervous system, which responds to and controls all processes occurring in the body - from mental to physiological. The functions of the brain are more extensive. The spinal cord is responsible for motor activity, touch, and sensation in the arms and legs. The membranes of the spinal cord perform specific tasks and ensure coordinated work to provide nutrition and remove metabolic products from brain tissue.

The structure of the spinal cord and surrounding tissues

If you carefully study the structure of the spine, it will become clear that the gray matter is securely hidden, first behind the movable vertebrae, then behind the membranes, of which there are three, followed by the white matter of the spinal cord, which ensures the conduction of ascending and descending impulses. As you go up the spinal column, the amount of white matter increases, as more controlled areas appear - arms, neck.

White matter is axons (nerve cells) covered with a myelin sheath.

Gray matter provides communication between internal organs and the brain using white matter. Responsible for memory processes, vision, emotional status. Gray matter neurons are not protected by the myelin sheath and are very vulnerable.

To simultaneously provide nutrition to the neurons of the gray matter and protect it from damage and infection, nature has created several obstacles in the form of the spinal membranes. The brain and spinal cord have identical protection: the membranes of the spinal cord are a continuation of the membranes of the brain. To understand how the spinal canal works, it is necessary to carry out a morphofunctional characterization of each individual part of it.

Functions of the hard shell

The dura mater is located just behind the walls of the spinal canal. It is the densest and consists of connective tissue. It has a rough structure on the outside, and the smooth side faces inward. The rough layer provides a tight seal with the vertebral bones and holds soft tissue in the spinal column. The smooth endothelium layer of the spinal cord dura is the most important component. Its functions include:

• production of hormones - thrombin and fibrin;
• exchange of tissue and lymphatic fluid;
• blood pressure control;
• anti-inflammatory and immunomodulatory.

During the development of the embryo, connective tissue comes from mesenchyme - cells from which blood vessels, muscles, and skin subsequently develop.

The structure of the outer shell of the spinal cord is determined by the necessary degree of protection of the gray and white matter: the higher, the thicker and denser it is. At the top it fuses with the occipital bone, and in the area of ​​the coccyx it thins out to several layers of cells and looks like a thread.

The same type of connective tissue forms a protection for the spinal nerves, which is attached to the bones and reliably fixes the central canal. There are several types of ligaments with which the external connective tissue is attached to the periosteum: these are lateral, anterior, and dorsal connecting elements. If it is necessary to remove the hard shell from the bones of the spine - a surgical operation - these ligaments (or cords) pose a problem for the surgeon due to their structure.

Arachnoid

The layout of the shells is described from external to internal. The arachnoid membrane of the spinal cord is located behind the dura mater. Through a small space it adjoins the endothelium from the inside and is also covered with endothelial cells. It looks translucent. The arachnoid membrane contains a huge number of glial cells that help generate nerve impulses, participate in the metabolic processes of neurons, secrete biologically active substances, and perform a support function.

The question of the innervation of the arachnoid film is controversial for physicians. It has no blood vessels. Also, some scientists consider the film as part of the soft shell, since at the level of the 11th vertebra they merge into one.

The median membrane of the spinal cord is called the arachnoid, as it has a very thin structure in the form of a web. Contains fibroblasts - cells that produce extracellular matrix. In turn, it ensures the transport of nutrients and chemicals. With the help of the arachnoid membrane, the cerebrospinal fluid moves into the venous blood.

The granulations of the middle shell of the spinal cord are villi, which penetrate the outer hard shell and exchange liquor fluid through the venous sinuses.

Inner shell

The soft shell of the spinal cord is connected to the hard shell with the help of ligaments. The wider area of ​​the ligament is adjacent to the soft shell, and the narrower area is adjacent to the outer shell. In this way, the three membranes of the spinal cord are fastened and fixed.

The anatomy of the soft layer is more complex. This is loose tissue containing blood vessels that deliver nutrition to neurons. Due to the large number of capillaries, the color of the fabric is pink. The soft membrane completely surrounds the spinal cord, its structure is denser than similar brain tissue. The membrane adheres so tightly to the white matter that with the slightest dissection it appears from the cut.

It is noteworthy that such a structure is found only in humans and other mammals.

This layer is well washed by blood and therefore performs a protective function, since the blood contains a large number of leukocytes and other cells responsible for human immunity. This is extremely important, since the entry of microbes or bacteria into the spinal cord can cause intoxication, poisoning and death of neurons. In such a situation, you can lose the sensitivity of certain areas of the body for which the dead nerve cells were responsible.

The soft shell has a two-layer structure. The inner layer is the same glial cells that are in direct contact with the spinal cord and provide its nutrition and removal of waste products, and also participate in the transmission of nerve impulses.

Spaces between the membranes of the spinal cord

The 3 shells do not touch each other tightly. Between them there are spaces that have their own functions and names.

Epidural the space is between the bones of the spine and the hard shell. Filled with adipose tissue. This is a kind of protection against lack of nutrition. In emergency situations, fat can become a source of nutrition for neurons, which will allow the nervous system to function and control processes in the body.

The looseness of adipose tissue is a shock absorber, which, under mechanical action, reduces the load on the deep layers of the spinal cord - the white and gray matter, preventing their deformation. The membranes of the spinal cord and the spaces between them represent a buffer through which the upper and deep layers of tissue communicate.

Subdural the space is between the dura mater and the arachnoid (arachnoid) membrane. It is filled with cerebrospinal fluid. This is the most frequently changing medium, the volume of which is approximately 150 - 250 ml in an adult. The fluid is produced by the body and is renewed 4 times a day. In just one day, the brain produces up to 700 ml of cerebrospinal fluid (CSF).

Liquor performs protective and trophic functions.

1. In case of mechanical impact - impact, fall, it maintains pressure and prevents deformation of soft tissues, even with breaks and cracks in the bones of the spine.
2. The liquor contains nutrients - proteins, minerals.
3. White blood cells and lymphocytes in the cerebrospinal fluid suppress the development of infection near the central nervous system by absorbing bacteria and microorganisms.

CSF is an important fluid that doctors use to determine if a person has had a stroke or brain injury that compromises the blood-brain barrier. In this case, red blood cells appear in the liquid, which should not normally be the case.

The composition of the cerebrospinal fluid changes depending on the work of other human organs and systems. For example, if there are disturbances in the digestive system, the liquid becomes more viscous, as a result of which the flow becomes more difficult and painful sensations appear, mainly headaches.

Decreased oxygen levels also disrupt the functioning of the nervous system. First, the composition of the blood and intercellular fluid changes, then the process is transferred to the cerebrospinal fluid.

A big problem for the body is dehydration. First of all, the central nervous system suffers, which, in difficult conditions of the internal environment, is not able to control the functioning of other organs.

The subarachnoid space of the spinal cord (in other words, subarachnoid) is located between the pia mater and the arachnoid. This is where the largest amount of liquor is located. This is due to the need to ensure the greatest safety of certain parts of the central nervous system. For example, the brainstem, cerebellum or medulla oblongata. There is especially a lot of cerebrospinal fluid in the area of ​​the trunk, since all the vital sections that are responsible for reflexes and breathing are located there.

If there is a sufficient amount of fluid, mechanical external influences on the area of ​​the brain or spine reach them to a much lesser extent, since the fluid compensates and reduces the impact from the outside.

In the arachnoid space, fluid circulates in various directions. The speed depends on the frequency of movements and breathing, that is, it is directly related to the work of the cardiovascular system. Therefore, it is important to maintain a regimen of physical activity, walking, proper nutrition and drinking water.

Cerebrospinal fluid exchange

Liquor enters the circulatory system through the venous sinuses and is then sent for purification. The system that produces the fluid protects it from the possible entry of toxic substances from the blood, and therefore selectively passes elements from the blood into the cerebrospinal fluid.

The membranes and intershell spaces of the spinal cord are washed by a closed system of cerebrospinal fluid, therefore, under normal conditions, they ensure stable functioning of the central nervous system.

Various pathological processes that begin in any part of the central nervous system can spread to neighboring ones. The reason for this is the continuous circulation of cerebrospinal fluid and the transfer of infection to all parts of the brain and spinal cord. Not only infectious, but also degenerative and metabolic disorders affect the entire central nervous system.

Cerebrospinal fluid analysis is key in determining the extent of tissue damage. The state of the cerebrospinal fluid makes it possible to predict the course of diseases and monitor the effectiveness of treatment.

Excess CO2, nitric and lactic acids are removed into the bloodstream so as not to create a toxic effect on nerve cells. We can say that the liquor has a strictly constant composition and maintains this constancy with the help of the body's reactions to the appearance of an irritant. A vicious circle occurs: the body tries to please the nervous system, maintaining balance, and the nervous system, with the help of streamlined reactions, helps the body maintain this balance. This process is called homeostasis. It is one of the conditions for human survival in the external environment.

Connection between shells

The connection between the membranes of the spinal cord can be traced from the earliest moment of formation - at the stage of embryonic development. At the age of 4 weeks, the embryo already has the rudiments of the central nervous system, in which various tissues of the body are formed from just a few types of cells. In the case of the nervous system, this is the mesenchyme, which gives rise to the connective tissue that makes up the membranes of the spinal cord.

In the formed body, some membranes penetrate one another, which ensures metabolism and the performance of general functions to protect the spinal cord from external influences.

Sheaths of the spinal cord. Dura mater, arachnoid mater, pia mater of the spinal cord. The spinal cord is covered with three connective tissue membranes, meninges, originating from the mesoderm. These shells are the following, if you go from the surface inwards: hard shell, duramater; arachnoid membrane, arachnoidea, and soft membrane, piamater. Cranially, all three membranes continue into the same membranes of the brain.

1. The hard shell of the spinal cord, duramaterspinalis, envelops the spinal cord in the form of a sac. It does not adhere closely to the walls of the spinal canal, which are covered with periosteum. The latter is also called the outer layer of the dura mater. Between the periosteum and the dura mater there is the epidural space, cavitas epiduralis. It contains fatty tissue and venous plexuses - plexusvenosivertebrales interni, into which venous blood flows from the spinal cord and vertebrae. Cranially, the hard shell fuses with the edges of the large foramen of the occipital bone, and caudally ends at the level of the II - III sacral vertebrae, tapering in the form of a thread, filumduraematrisspinalis, which is attached to the coccyx.

2. The arachnoid membrane of the spinal cord, arachnoideaspinalis, in the form of a thin transparent avascular sheet, is adjacent to the hard shell from the inside, separated from the latter by a slit-like subdural space, pierced by thin bars, spatium subdurale. Between the arachnoid membrane and the soft membrane directly covering the spinal cord there is a subarachnoid space, cavitassubarachnoidalis, in which the brain and nerve roots lie freely, surrounded by a large amount of cerebrospinal fluid, liquorcere-brospinalis. This space is especially wide in the lower part of the arachnoid sac, where it surrounds the caudaequina of the spinal cord (cisternaterminalis). The fluid filling the subarachnoid space is in continuous communication with the fluid of the subarachnoid spaces of the brain and cerebral ventricles. Between the arachnoid membrane and the soft membrane covering the spinal cord in the posterior cervical region, along the midline, a septum, septumcervicdleintermedium, is formed. In addition, on the sides of the spinal cord in the frontal plane there is a dentate ligament, lig. denticulatum, consisting of 19 - 23 teeth passing in the spaces between the anterior and posterior roots. The dentate ligaments serve to hold the brain in place, preventing it from stretching out in length. Through both ligg. denticulatae, the subarachnoid space is divided into anterior and posterior sections.

3. The soft membrane of the spinal cord, piamaterspinalis, covered on the surface with endothelium, directly envelops the spinal cord and contains vessels between its two layers, together with which it enters its grooves and the medulla, forming perivascular lymphatic spaces around the vessels.

8. Development of the brain (brain vesicles, parts of the brain).

The brain is located in the cranial cavity. Its upper surface is convex, and its lower surface - the base of the brain - is thickened and uneven. At the base of the brain, 12 pairs of cranial (or cranial) nerves arise from the brain. The brain is divided into the cerebral hemispheres (the most recent part in evolutionary development) and the brainstem with the cerebellum. The weight of the adult brain is on average 1375 g for men, 1245 g for women. The weight of the brain of a newborn is on average 330 - 340 g. In the embryonic period and in the first years of life, the brain grows rapidly, but only by the age of 20 it reaches its final size.

Scheme Brain Development

A. The neural tube in a longitudinal section, three brain vesicles are visible (1, 2 and 3); 4 - part of the neural tube from which the spinal cord develops.
B. Lateral view of the fetal brain (3rd month) - five brain vesicles; 1 - end brain (first vesicle); 2 - diencephalon (second bladder); 3 - midbrain (third bladder); 4 - hindbrain (fourth bladder); 5 - medulla oblongata (fifth cerebral vesicle).

The brain and spinal cord develop on the dorsal (dorsal) side of the embryo from the outer germ layer (ectoderm). At this point, the neural tube is formed with an expansion in the head section of the embryo. Initially, this expansion is represented by three brain vesicles: anterior, middle and posterior (diamond-shaped). Subsequently, the anterior and rhomboid vesicles divide and five brain vesicles are formed: terminal, intermediate, middle, posterior and oblong (accessory).

During development, the walls of the brain vesicles grow unevenly: either thickening, or remaining thin in some areas and pushing into the cavity of the vesicle, participating in the formation of the choroid plexuses of the ventricles.

The remnants of the cavities of the brain vesicles and the neural tube are the cerebral ventricles and the central canal of the spinal cord. From each brain vesicle certain parts of the brain develop. In this regard, out of the five cerebral vesicles in the brain, five main sections are distinguished: medulla oblongata, hindbrain, midbrain, diencephalon and telencephalon.