Clinical anatomy of the spine and spinal cord. The structure and function of the meninges of the spinal cord Which meninges surround the spinal cord

The spinal cord is outside covered with membranes, which 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 the metabolism of nervous tissue. Cerebrospinal fluid circulates between the membranes, which is responsible for metabolism.

The spinal cord and the brain are parts of the central nervous system, which is responsible for and controls all processes in the body - from mental to physiological. The functions of the brain are more extensive. The spinal cord is responsible for motor activity, touch, sensitivity of the hands and feet. The membranes of the spinal cord perform specific tasks and provide coordinated work to provide nutrition and remove metabolic products from the 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 reliably hidden first behind the mobile vertebrae, then behind the membranes, of which there are three, then the white matter of the spinal cord, which ensures the conduction of ascending and descending impulses. As you climb up the spinal column, the amount of white matter increases, as more control areas appear - arms, neck.

The white matter is the axons (nerve cells) covered by the myelin sheath.

The gray matter connects the internal organs to the brain using white matter. Responsible for memory processes, vision, emotional status. Gray matter neurons are not protected by the myelin sheath and are highly vulnerable.

In order to simultaneously feed 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 defenses: the lining of the spinal cord is an extension of the lining of the brain. To understand how the spinal canal works, it is necessary to carry out the morphofunctional characteristics of each individual part of it.

Hard shell functions

The dura mater is located just behind the walls of the spinal canal. It is the most dense, consists of connective tissue... From the outside it has a rough structure, and the smooth side faces inward. The rough layer ensures tight connection with the vertebral bones and holds soft tissue in the spinal column. The smooth endothelial layer of the dura mater of the spinal cord 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.

Connective tissue in the process of development of the embryo comes from the mesenchyme - cells from which vessels, muscles, and skin subsequently develop.

The structure of the outer shell of the spinal cord is due to the necessary degree of protection of gray and white matter: the higher, the thicker and denser. At the top, it grows together with the occipital bone, and in the coccyx area it becomes thinner to several layers of cells and looks like a thread.

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

Arachnoid

The layout of the shells is described from outer to inner. The arachnoid membrane of the spinal cord is located behind the solid. 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, release biologically active substances, and perform a supporting function.

Controversial for physicians is the question of the innervation of the spider web. There are no blood vessels in it. Also, some scientists consider the film as part of the soft shell, since at the level of the 11th vertebra they merge into one whole.

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

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

Inner shell

The pia mater of the spinal cord is connected to the hard by means of ligaments. With a wider area, the ligament is adjacent to the soft shell, and a narrower one - to the outer shell. Thus, the three membranes of the spinal cord are fastened and fixed.

The anatomy of the soft layer is more complex. This is a loose fabric in which there are blood vesselsdelivering nutrition to neurons. Due to the large number of capillaries, the color of the tissue is pink. The pia mater completely surrounds the spinal cord, which is more dense in structure than similar brain tissue. The shell adheres so tightly to the white matter that at the slightest dissection it appears from the incision.

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

This layer is well washed by the blood and, thanks to this, performs a protective function, since the blood contains a large number of leukocytes and other cells that are responsible for human immunity. This is extremely important, since the ingress of microbes or bacteria into the spinal cord can cause intoxication, poisoning and neuronal death. In such a situation, you can lose the sensitivity of certain parts 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 the removal of decay products, and also participate in the transmission of nerve impulses.

The spaces between the membranes of the spinal cord

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 dura mater. Filled with fatty tissue. This is a kind of protection against lack of nutrition. In emergencies, fat can be a source of nutrition for neurons, allowing 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 - white and gray matter, preventing their deformation. The membranes of the spinal cord and the spaces between them are a buffer through which the upper and deep layers of tissue communicate.

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

Liquor performs protective and trophic functions.

1. Under mechanical action - impact, fall, retains pressure and prevents deformation of soft tissues, even with fractures and cracks of the bones of the spine.
2. The cerebrospinal fluid contains nutrients - proteins, minerals.
3. Leukocytes 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 a stroke or brain damage that disrupts the blood-brain barrier. In this case, erythrocytes appear in the liquid, which should not normally be.

The composition of the cerebrospinal fluid varies depending on the work of other human organs and systems. For example, in case of 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 nervous system. First, the composition of the blood and intercellular fluid changes, then the process is transmitted to the cerebrospinal fluid.

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

The subarachnoid space of the spinal cord (in other words, the subarachnoid) is located between the pia mater and the arachnoid. The largest amount of cerebrospinal fluid is located here. This is due to the need to ensure the greatest safety in some parts of the central nervous system. For example - the trunk, cerebellum or medulla oblongata. There is especially a lot of cerebrospinal fluid in the area of \u200b\u200bthe trunk, since there are all the vital departments that are responsible for reflexes and breathing.

In the presence of a sufficient amount of fluid, mechanical external influences on the area of \u200b\u200bthe 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 different directions. The speed depends on the frequency of movements, breathing, that is, it is directly related to work of cardio-vascular system... Therefore, it is important to observe the regime of physical activity, walking, proper nutrition and drinking water.

Cerebrospinal fluid exchange

Liquor through the venous sinuses enters the circulatory system and is then sent for cleaning. The system that produces the liquid protects it from the possible ingress of toxic substances from the blood, therefore it selectively passes the 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 provide stable operation 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.

Analysis of cerebrospinal fluid is central to determining the extent of tissue damage. The state of the cerebrospinal fluid allows predicting the course of diseases and monitoring the effectiveness of treatment.

Excess CO2, nitric and lactic acids are removed into the bloodstream so as not to create toxic effects on nerve cells. We can say that the cerebrospinal fluid 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 well-oiled 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.

Communication of shells with each other

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 make up the lining of the spinal cord.

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

Spinal cord arachnoid

Skull section showing the lining of the brain

Arachnoid (arachnoid) meninges - One of the three membranes that cover the brain and spinal cord. It is located between the other two membranes - the most superficial dura mater and the deepest pia mater, separating from the latter by a subarachnoid (subarachnoid) space filled with 120-140 ml of cerebrospinal fluid. The subarachnoid space contains blood vessels. In the lower part of the spinal canal in the cerebrospinal fluid of the subarachnoid space, the roots of the spinal nerves ("cauda equina") float freely.

Cerebrospinal fluid enters the subarachnoid space from the holes in the fourth ventricle of the brain, its greatest amount is contained in the cisterns of the subarachnoid space - extensions located above the large cracks and furrows of the brain.

The arachnoid, as the name suggests, has the appearance of a thin web formed by connective tissue, contains a large number of fibroblasts. Multiple filamentous branching cords (trabeculae) depart from the arachnoid membrane, which are woven into the pia mater. On both sides, the arachnoid membrane is covered with glial cells.

The arachnoid membrane forms villous outgrowths - pachyon granulations (lat. granulationes arachnoidales), protruding into the lumen of the venous sinuses formed by the dura mater, as well as into the blood and lymphatic capillaries at the exit site of the cranial and spinal nerve roots from the cranial cavity and spinal canal. Through granulation, the cerebrospinal fluid is reabsorbed through the layer of glial cells and the endothelium of the sinus into the venous blood. With age, the number and size of the villi increase.

The arachnoid and pia mater are sometimes considered as a common structure, the leptomeninx (Greek. leptomeninx), while the dura mater is called pachymeninx (Greek. pachymeninx).

Illustrations

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See what the "Arachnoid membrane of the spinal cord" is in other dictionaries:

Spinal cord membranes (meninges medullae spinalis) of the spinal canal - Cross section at the level of the intervertebral disc. the dura mater of the spinal cord; epidural space; arachnoid; posterior root of the spinal nerve: anterior root; spinal cord; spinal nerve; subarachnoid ... ... Human Anatomy Atlas

arachnoid shell - (arachnoidea) a thin connective tissue shell located between the hard and soft shells. It covers the brain without going into the grooves and crevices of the brain, in contrast to the deeper soft membrane. Therefore, between these shells ... ... Glossary of terms and concepts in human anatomy

Central nervous system (CNS) I. Cervical nerves. II. Pectoral nerves. III. Lumbar nerves. IV. Sacral nerves. V. Coccygeal nerves. / 1. Brain. 2. Diencephalon. 3. Midbrain... 4. The bridge. 5. Cerebellum. 6. The medulla oblongata. 7.…… Wikipedia

- (meninges) connective tissue structures that cover the brain and spinal cord. Distinguish between hard shell (dura mater, pachymeninx), arachnoid (arachnoidea) and vascular, or soft (vasculosa, pia mater). The arachnoid and soft shells unite ... ... Medical encyclopedia

Spinal cord - (medulla spinalis) (Fig. 254, 258, 260, 275) is a cord of brain tissue located in the spinal canal. Its length in an adult reaches 41 45 cm, and its width is 1 1.5 cm. The upper part of the spinal cord smoothly turns into ... ... Human Anatomy Atlas - (Encephalon). A. Anatomy of the human brain: 1) structure of G. of the brain, 2) membranes of the brain, 3) blood circulation in G. of the brain, 4) brain tissue, 5) course of fibers in the brain, 6) weight of the brain. B. Embryonic development of G. of the brain in vertebrates. WITH.… … Encyclopedic Dictionary of F.A. Brockhaus and I.A. Efron

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The human spinal cord is much inferior in complexity to the brain. But it is also quite complicated. Thanks to this, the human nervous system can harmoniously interact with muscles and internal organs.

It is surrounded by three shells that are different from each other. There are spaces in between, also needed for nutrition and protection. How are the membranes of the spinal cord arranged? What are their functions? And what other structures can you see next to them?

Location and structure

In order to understand the functions of the structures of the human skeleton, it is necessary to know well how they are arranged, where they are and with what other parts of the body they interact. That is, first of all, you need to find out the anatomical characteristics.

The spinal cord is surrounded by 3 membranes of connective tissue. Each of them then passes into the corresponding membrane of the brain. They develop from the mesoderm (that is, the middle germ layer) during intrauterine development, but differ from each other in appearance and structure.

The sequence of location, starting from the inside:

1. Soft or internal - is located around the spinal cord.
2. Average, spiderweb.
3. Hard or external - located near the walls of the spinal canal.

Details of the structure of each of these structures and their location in the spinal canal are briefly discussed below.

Soft

The inner shell, which is also called soft, tightly wraps directly around the spinal cord. It is a loose connective tissue, very soft, which is evident even from the name. In its composition, two sheets are distinguished, between which there are a lot of blood vessels. The outer part is covered with endothelium.

Small ligaments begin from the outer leaf, which are connected to the hard shell. These ligaments are called dentate ligaments. The junction points coincide with the exit sites of the anterior and posterior nerve roots. These ligaments are very important for fixing the spinal cord and its integuments, do not allow it to stretch in length.

Spiderweb

The middle shell is called arachnoid. It looks like a thin translucent plate that connects to the hard shell at the point where the roots exit. Also covered with endothelial cells.

There are no vessels at all in this structural part. It is not entirely solid, since there are small slit-like holes along the entire length in places. Separates the subdural and subarachnoid spaces in which one of the most important fluids is located human body - CSF.

Solid

The outer or hard shell is the most massive, consists of two sheets and looks like a cylinder. The outer leaf is rough and directed towards the walls of the spinal canal. Internal smooth, shiny, covered with endothelium.

It is widest in the region of the foramen magnum, where it partially fuses with the periosteum of the occipital bone. Heading down, the cylinder narrows noticeably and attaches to the coccyx periosteum in the form of a cord or thread.

From the tissue of the dura mater, receptacles are formed for each spinal nerve. They, gradually expanding, go towards the intervertebral foramen. The spine, or rather, its posterior longitudinal ligament, is attached with the help of small bridges made of connective tissue. Thus, there is fixation to the bone part of the skeleton.

Functions

All 3 membranes of the spinal cord are necessary for the proper functioning of the nervous system, in particular, the implementation of coordinated movements and adequate sensitivity of almost the entire body. These functions of the spinal cord can be fully manifested only if all of its structural components are intact.

Among the most important aspects of the role of the 3 meninges of the spinal cord are:

• Protection. Several connective tissue plates, which differ in thickness and structure, protect the substance of the spinal cord from shock, shock and any other mechanical influences. The bone tissue of the spine has a fairly large load during movement, but in a healthy person this will not affect the state of the intravertebral structures.


• Delimitation of spaces. Between the connective tissue structures, there are spaces that are filled with objects and substances important for the body. This will be discussed in more detail below. Due to the fact that they are limited from each other and from external environment, sterility and the ability to function correctly are preserved.
• Fixation. The soft shell is attached directly to the spinal cord, along the entire length of the ligaments, it is firmly connected to the hard, and that - to the ligament that fixes bone structures spine. Thus, along its entire length, the spinal cord is firmly fixed and cannot move and stretch.
• Ensuring sterility. Thanks to a reliable barrier, the spinal cord and cerebrospinal fluid are sterile, bacteria from the external environment cannot get there. Infection occurs only when damaged or if a person suffers from very serious diseases in severe stages (some variants of tuberculosis, neurosyphilis).
• Conducting the structures of the nervous tissue (anterior and posterior roots of the nerves, and in some places the trunk of the nerve) and vessels, a receptacle for them.

Each of the 3 membranes is very important and is an irreplaceable structure of the skeleton of the human body. Thanks to them, complete protection from infections and mechanical damage to a part of the central nervous system and small areas of nerves that go to the peripheral parts of the body is provided.

Spaces

Between the membranes, as well as between them and the bone, there are three spaces of the spinal cord. Each of them has its own name, structure, size and content.

List of spaces starting from outside:

1. Epidural, between the dura and the inner surface bone tissue spinal canal. It contains a huge number of vertebral plexuses of blood vessels, which are shrouded in fatty tissue.
2. Subdural, between hard and arachnoid. It is filled with cerebrospinal fluid, that is, cerebrospinal fluid. But there is very little of it here, since this space is very small.
3. Subarachnoid, between the arachnoid and soft membranes. This space expands in the lower sections. It contains up to 140 ml of liquor. For analysis, it is usually taken from this very space in the area under the second lumbar vertebra.

These 3 spaces are also very important for the protection of the medulla, to some extent even the one in the head of the nervous system.

Backs

Spinal cord with everyone structural componentsincluded in its composition, divided into segments. A pair of spinal nerves emerge from each segment. Each nerve begins with two roots, which unite before exiting the intervertebral foramen. The roots are also protected by the dura mater.

The anterior root is responsible for motor function, and the posterior root is responsible for sensitivity. With injuries to the membranes of the spinal cord, there is a high risk of damage to one of them. In this case, the corresponding symptomatology develops: paralysis or convulsions if the anterior roots are damaged, and the lack of adequate sensitivity if the posterior ones are affected.

All the structures described above are very important for the full functioning of the body, the innervation of most of the integuments of the body and most of the internal organs, as well as for the transmission of signals from receptors to the central nervous system. In order not to disrupt the interaction, it is important to monitor the health of the spine and the muscles that strengthen it, since without the correct location of the musculoskeletal elements, correct fixation is impossible, the risks of infringement and the development of hernias increase.

Spinal cord (medulla spinalis) confined inside the spinal canal (sapalis vertebralis). The spinal cord above is connected directly with the medulla oblongata, below it ends with a short cerebral cone (conus medullaris), passing into the terminal thread (filum terminate).

The spinal cord is divided into four parts: the cervical (pars cervicalis),chest (pars thoracica),lumbar (pars lumbalis),sacral (parssacralis).The spinal cord segments correspond to the vertebrae. In the upper and middle cervical regions (CI - IV), the segment number corresponds to the number of the vertebra, in the lower cervical and upper thoracic regions (C VI -Th III) - a difference of 1 in favor of the segment, in the middle thoracic regions (Th VI - VII,) - a difference of 2 in favor of the segment, in the lower thoracic (Th VIII - X) - a difference of 3 in favor of the segment, the vertebra L, the segments L IV -SV correspond. The spinal cord forms two thickenings: the cervical (intumescentia cervicalis), lying from the V cervical to I thoracic vertebra, and the lumbosacral (intumescentia lumbosacralis), concluded between the I lumbar and II sacral vertebrae.

The anterior median fissure is located on the anterior surface of the spinal cord. (fissura mediana anterior), behind is the posterior median sulcus (sulcus medianus posterior). A front rope lies ahead (funiculus anterior), on the side of it is a lateral cord (funiculus lateralis), behind - posterior cord (funiculus posterior). These cords are separated from each other by grooves: anterolateral (sulcus anterolateralis), posterolateral (sulcus posterolateralis), as well as the described anterior and posterior median fissures.

On the cut, the spinal cord consists of gray matter (substantia grisea), located in the center, and white matter (substantia alba), lying on the periphery. The gray matter is located in the form of the letter N. It forms an anterior horn on each side (cornu anterius), rear horn (cornu posterius) and central gray matter (substantia grisea centralis). In the center of the latter is the central channel (canalis centralis), at the top communicating with the IV ventricle, and at the bottom passing into the terminal ventricle (ventriculus terminalis).

The membranes and intercostals of the spinal cord

In the spinal cord, there are soft, arachnoid and hard membranes:

Spinal cord piazza (pia mater spinalis) tightly covers the substance of the brain, contains many vessels.

Spinal cord arachnoid (andracehnoidea spinalis) thin, with fewer vessels.

Spinal cord dura mater (dura mater spinalis) - a dense connective tissue plate that covers the arachnoid membrane. Unlike the dura mater of the brain, it is divided into two sheets: outer and inner. the outer layer fits snugly to the walls of the spinal canal and is closely connected with the periosteum and its ligamentous apparatus. The inner layer, or the dura mater itself, extends from the foramen magnum to the II-III sacral vertebra, forming a dural sac that encloses the spinal cord. On the sides of the spinal canal, the dura mater gives out processes that make up the vagina for the spinal nerves that exit the canal through the intervertebral foramen.

In the spinal cord, spaces are distinguished:

Between the outer and inner layers of the dura mater there is an epidural (epidural) space (cavum epidurale).

Subdural space (cavum subdurale) - the slit space between the hard and arachnoid membranes of the spinal cord.

Subarachnoid space (cavum subarachnoidealis) located between the arachnoid and soft membranes of the spinal cord, filled with cerebrospinal fluid. The bundles of connective tissue between the arachnoid and pia mater are especially strongly developed on the sides, between the anterior and posterior roots of the spinal cord, where they form the dentate ligaments (ligg.denticulata) associated with the dura mater. these ligaments run in the frontal plane throughout the dural sac up to the lumbar spine and divide the subarachnoid space into two chambers: anterior and posterior.

The subarachnoid space of the spinal cord passes directly into the same space of the brain with its cisterns. The largest of them - cisterna cerebellomedullaris - communicates with the cavity of the IV ventricle of the brain and the central canal of the spinal cord. The part of the dural sac, located between the II lumbar and II sacral vertebrae, is filled with the cauda equina with the filum terminale of the spinal cord and cerebrospinal fluid. Lumbar puncture (puncture of the subarachnoid space), performed below the II lumbar vertebra, is the safest, because the spinal cord stem does not reach here.

Dear colleagues, the material offered to you was once prepared by the author for the chapter of the manual on neuraxial anesthesia, which, for a number of reasons, has not been completed or published. We believe that the information presented below will be of interest not only to novice anesthesiologists, but also to experienced specialists, since it reflects the most modern ideas about the anatomy of the spine, epidural and subarachnoid spaces from the point of view of the anesthesiologist.

Spine anatomy

As you know, the vertebral column consists of 7 cervical, 12 thoracic and 5 lumbar vertebrae with the adjacent sacrum and coccyx. It has several clinically significant bends. The greatest bends anteriorly (lordosis) are located at levels C5 and L4-5, posteriorly at levels Th5 and S5. These anatomical features in conjunction with the baricity of local anesthetics play an important role in the segmental distribution of the level of the spinal block.

The peculiarities of individual vertebrae affect the technique, primarily of epidural puncture. The spinous processes extend at different angles at different levels of the spine. In the cervical and lumbar regions, they are located almost horizontally in relation to the plate, which facilitates the median access when the needle is perpendicular to the axis of the spine. At the mid-thoracic level (Th5-9), the spinous processes extend at rather sharp angles, which makes the paramedial approach preferable. The processes of the upper thoracic (Th1-4) and lower thoracic (Th10-12) vertebrae are oriented intermediate in comparison with the above two features. At these levels, none of the accesses has any advantages over the other.

Access to the epidural (EP) and subarachnoid space (SP) is between the plates (interlaminar). The superior and inferior articular processes form the facet joints, which play an important role in the correct positioning of the patient prior to EP puncture. The correct positioning of the patient prior to EP puncture is determined by the orientation of the facet joints. Since the facet joints of the lumbar vertebrae are oriented in the sagittal plane and provide flexion back and forth, maximum flexion of the spine (fetal position) increases the interlaminar spaces between the lumbar vertebrae.

The facet joints of the thoracic vertebrae are oriented horizontally and provide rotational movements of the spine. Consequently, excessive flexion of the spine does not provide additional advantages for EP puncture at the thoracic level.

Anatomical bone landmarks

Identification of the required intervertebral space is the key to the success of the epidural and spinal anesthesiaas well as a necessary condition for patient safety.

In a clinical setting, the choice of the puncture level is carried out by the anesthesiologist by palpation in order to identify certain bony landmarks. It is known that the 7th cervical vertebra has the most pronounced spinous process. At the same time, it should be borne in mind that in patients with scoliosis, the spinous process of the 1st thoracic vertebra may be most prominent (in about ⅓ of patients).

The line joining the lower angles of the scapula passes through the spinous process of the 7th thoracic vertebra, and the line joining the iliac crests (Tuffier's line) passes through the 4th lumbar vertebra (L4).

Identification of the required intervertebral space using bony landmarks is far from always correct. The results of a study by Broadbent et al. (2000), in which one of the anesthesiologists using a marker marked a certain intervertebral space at the lumbar level and tried to identify its level in the sitting position of the patient, the second made the same attempt with the patient on his side. Then, a contrast marker was attached over the mark, and magnetic resonance imaging was performed.

Most often, the true level at which the mark was made was one to four segments lower than the values \u200b\u200breported by the anesthesiologists participating in the study. It was possible to correctly identify the intervertebral space only in 29% of cases. The accuracy of the determination did not depend on the position of the patient, but worsened in overweight patients. By the way, the spinal cord ended at the L1 level only in 19% of patients (in the rest at the L2 level), which posed the threat of its damage in case of a wrong choice high level puncture. What makes it difficult to choose the right intervertebral space?

There is evidence that the Tuffier line corresponds to the L4 level in only 35% of people (Reynolds F., 2000). For the remaining 65%, this line is located at the level from L3-4 to L5-S1.

It should be noted that an error of 1-2 segments when choosing the level of puncture of the epidural space, as a rule, does not affect the effectiveness of epidural anesthesia and analgesia.

Spine ligaments

The anterior longitudinal ligament runs along the front surface of the vertebral bodies from the skull to the sacrum, which is rigidly fixed to the intervertebral discs and the edges of the vertebral bodies. The posterior longitudinal ligament connects the posterior surfaces of the vertebral bodies and forms the anterior wall of the spinal canal.

The vertebral plates are connected by a yellow ligament, and the posterior spinous processes are connected by interspinous ligaments. The supraspinous ligament runs along the outer surface of the spinous processes C7-S1. The legs of the vertebrae are not connected by ligaments, as a result, intervertebral foramen are formed, through which the spinal nerves exit.

The yellow ligament consists of two sheets, spliced \u200b\u200balong the midline at an acute angle. In this regard, it seems to be stretched in the form of an "awning". In the cervical and thoracic regions, the ligamentum flavum may not be spliced \u200b\u200balong the midline, which causes problems in identifying EP by the resistance loss test. The yellow ligament is thinner along the midline (2-3 mm) and thicker at the edges (5-6 mm). In general, it has the greatest thickness and density at the lumbar (5-6 mm) and thoracic levels (3-6 mm), and the smallest in cervical spine (1.53 mm). Together with the vertebral arches, the yellow ligament forms the back wall of the spinal canal.

When the needle is passed through the median approach, it must pass through the supraspinous and interspinous ligaments, and then through the yellow ligament. With paramedial access, the needle bypasses the supraspinous and interspinous ligaments, immediately reaching the yellow ligament. The yellow ligament is denser than others (80% consists of elastic fibers), therefore, an increase in resistance when passing it with a needle, with its subsequent loss, is known to be used to identify EP.

The distance between the yellow ligament and the dura mater in the lumbar spine does not exceed 5-6 mm and depends on factors such as arterial and venous pressure, pressure in the spinal canal, pressure in abdominal cavity (pregnancy, abdominal compartment syndrome, etc.) and chest cavity (IVL).

With age, the yellow ligament thickens (ossifies), which makes it difficult to pass a needle through it. This process is most pronounced at the level of the lower thoracic segments.

Spinal cord membranes

The spinal canal has three connective tissue membranes that protect the spinal cord: the dura mater, arachnoid (arachnoid) membrane, and the pia mater. These membranes are involved in the formation of three spaces: epidural, subdural and subarachnoid. The spinal cord (SM) and roots are directly covered by a well-vascularized pia mater, the subarachnoid space is limited by two adjacent membranes - arachnoid and dura mater.

All three membranes of the SM continue in the lateral direction, forming the connective tissue covering of the spinal roots and mixed spinal nerves (endoneurium, perineurium, and epineurium). The subarachnoid space also extends over a short length along the roots and spinal nerves, ending at the level of the intervertebral foramen.

In some cases, the cuffs formed by the dura mater lengthen by a centimeter or more (in rare cases, by 6-7 cm) along the mixed spinal nerves and significantly extend beyond the intervertebral foramen. This fact must be taken into account when performing a blockade. brachial plexus from the supraclavicular approaches, since in these cases, even with the correct orientation of the needle, intrathecal injection of a local anesthetic is possible with the development of a total spinal block.

The dura mater (DM) is a sheet of connective tissue consisting of collagen fibers oriented both transversely and longitudinally, as well as a number of elastic fibers oriented longitudinally.

For a long time, it was believed that TMO fibers have a predominantly longitudinal orientation. In this regard, it was recommended to orient the cut of the spinal needle with the cutting tip vertically during puncture of the subarachnoid space, so that it does not cross the fibers, but as if spread them. Later, using electron microscopy, a rather disordered arrangement of TMO fibers was revealed - longitudinal, transverse and partially circular. The thickness of the dura mater is variable (from 0.5 to 2 mm) and may differ at different levels in the same patient. The thicker the dura mater, the higher its ability to retraction (retraction) of the defect.

The dura mater, the thickest of all the membranes of the SM, has long been considered the most significant barrier between EP and underlying tissues. In reality, this is not the case. Experimental studies with morphine and alfentanil, performed on animals, have shown that the dura mater is the most permeable membrane of the CM (Bernards C., Hill H., 1990).

The false conclusion about the leading barrier function of the dura mater in the diffusion pathway led to an incorrect interpretation of its role in the genesis of post dural puncture headache (PPHB). If we assume that PPH is caused by leakage of cerebrospinal fluid (CSF) through a puncture defect in the membranes of the CM, we must draw the correct conclusion about which of them is responsible for this leak.

Since CSF is located under the arachnoid membrane, it is the defect of this membrane, and not the dura mater, that plays a role in the mechanisms of PPHP. Currently, there is no evidence indicating that it is the defect in the membranes of the CM, and therefore its shape and size, as well as the rate of CSF loss (and therefore the size and shape of the needle tip) that affect the development of PPHB.

This does not mean that clinical observations indicating that the use of thin needles, pencil-point needles, and vertical orientation of the Quincke needles reduce the incidence of PDPH are incorrect. However, the explanations for this effect are incorrect, in particular, the statements that in the vertical orientation of the cut, the needle does not cross the fibers of the dura mater, but "pushes" them apart. These statements completely ignore modern ideas about the anatomy of the dura mater, consisting of randomly located fibers, rather than vertically oriented. At the same time, the cells of the arachnoid membrane have a cephalo-caudal orientation. In this regard, in the longitudinal orientation of the cut, the needle leaves a narrow slit-like opening in it, damaging fewer cells than in the perpendicular orientation. However, this is only an assumption that requires serious experimental confirmation.

Arachnoid

The arachnoid membrane consists of 6-8 layers of flat epithelial-like cells located in one plane and overlapping each other, tightly connected to each other and having a longitudinal orientation. The arachnoid membrane is not just a passive reservoir for CSF, it is actively involved in the transport of various substances.

Not so long ago, it was found that metabolic enzymes are produced in the arachnoid, which can affect the metabolism of certain substances (for example, adrenaline) and neurotransmitters (acetylcholine), which are important for the implementation of the mechanisms of spinal anesthesia. Active transport of substances through the arachnoid membrane is carried out in the area of \u200b\u200bthe cuffs of the spinal roots. Here there is a unilateral movement of substances from the CSF to the EP, which increases the clearance of local anesthetics introduced into the SP. The lamellar structure of the arachnoid membrane contributes to its easy separation from the dura mater with spinal puncture.

The thin arachnoid membrane, in fact, provides more than 90% resistance in the pathway of diffusion of drugs from the EP to the CSF. The fact is that the distance between the randomly oriented collagen fibers of the TMO is large enough to create a barrier on the path of molecules medicines... In contrast, the cellular architectonics of the arachnoid membrane provides the greatest obstacle to diffusion and explains the fact that CSF is located in the subarachnoid space, but not in the subdural space.

Awareness of the role of the arachnoid membrane as the main barrier to diffusion from EP to CSF \u200b\u200ballows a new look at the dependence of the diffusion capacity of drugs on their ability to dissolve in fats. Traditionally, it is believed that more lipophilic drugs are characterized by greater diffusion capacity. This is the basis of the recommendations for the preferred use of lipophilic opioids (fentanyl) for EA, which provide rapidly developing segmental analgesia. At the same time, in experimental studies it was found that the permeability of hydrophilic morphine through the membranes of the spinal cord does not differ significantly from that of fentanyl (Bernards C., Hill H., 1992). It was found that 60 minutes after the epidural injection of 5 mg of morphine at the L3-4 level are determined in the cerebrospinal fluid already at the level of the cervical segments (Angst M. et al., 2000).

The explanation for this is the fact that diffusion from the epidural to the subarachnoid space occurs directly through the cells of the arachnoid membrane, since the intercellular connections are so dense that they exclude the possibility of penetration of molecules between cells. In the process of diffusion, the drug must penetrate the cell through the double lipid membrane, and then, once again overcoming the membrane, enter the SP. The arachnoid membrane consists of 6-8 layers of cells. Thus, during the diffusion process, the above process is repeated 12-16 times.

Drugs with high fat solubility are thermodynamically more stable in the lipid bilayer than in the aqueous intra- or extracellular space; therefore, it is more difficult for them to leave the cell membrane and move into the extracellular space. Thus, their diffusion through the arachnoid membrane slows down. Preparations with poor solubility in fats have the opposite problem - they are stable in an aqueous medium, but hardly penetrate the lipid membrane, which also slows down their diffusion.

Preparations with an intermediate ability to dissolve in fats are least susceptible to the above water-lipid interactions.

At the same time, the ability to penetrate the membranes of the CM is not the only factor that determines the pharmacokinetics of drugs introduced into the EP. Another important factor (which is often ignored) is the volume of their absorption (sequestration) by EPO adipose tissue. In particular, it was found that the duration of stay of opioids in EP is linearly dependent on their ability to dissolve in fats, since this ability determines the volume of drug sequestration in adipose tissue. Due to this, the penetration of lipophilic opioids (fentanyl, sufentanil) to the CM is hampered. There is good reason to believe that with continuous epidural infusion of these drugs, the analgesic effect is achieved mainly due to their absorption into the bloodstream and suprasegmental (central) action. In contrast, with bolus administration, the analgesic effect of fentanyl is mainly due to its action at the segmental level.

Thus, the widespread notion that drugs with a greater ability to dissolve in fats after epidural administration penetrate the CM more quickly and easily is not entirely correct.

Epidural space

The EP is part of the spinal canal between its outer wall and the dura mater, extending from the foramen magnum to the sacrococcygeal ligament. The dura mater is attached to the foramen magnum, as well as to the 1st and 2nd cervical vertebrae; therefore, the solutions introduced into the EP cannot rise above this level. EP is located anterior to the plate, laterally bounded by the legs, and in front by the vertebral body.

EP contains:

• adipose tissue,
• spinal nerves leaving the spinal canal through the intervertebral foramen,
• blood vessels that feed the vertebrae and spinal cord.

The vessels of the EP are mainly represented by epidural veins, which form powerful venous plexuses with a predominantly longitudinal arrangement of vessels in the lateral parts of the EP and a multitude of anastomotic branches. EP has a minimum filling in the cervical and thoracic spine, maximum - in the lumbar spine, where the epidural veins have a maximum diameter.

Descriptions of EN anatomy in most guidelines for regional anesthesia present adipose tissue as a homogeneous layer adjacent to the dura mater and filling the EN. The veins of the ER are usually depicted as a continuous network (Batson's venous plexus) adjacent to the CM along its entire length. Although back in 1982, data from studies performed using CT and contrasting veins with EP were published (Meijenghorst G., 1982). According to these data, epidural veins are located mainly in the anterior and partly in the lateral parts of the EP. Later, this information was confirmed in the works of Hogan Q. (1991), who showed, in addition, that adipose tissue in the EP is arranged in the form of separate "packages" located mainly in the posterior and lateral parts of the EP, that is, it does not have a continuous character. layer.

The anteroposterior size of the EP narrows progressively from the lumbar level (5-6 mm) to the thoracic level (3-4 mm) and becomes minimal at the C3-6 level.

Under normal conditions, the pressure in the EA is negative. It is lowest in the cervical and thoracic regions. Increased pressure in chest when coughing, the Valsalva test leads to an increase in pressure in the EP. The introduction of liquid into the EP increases the pressure in it, the magnitude of this increase depends on the speed and volume of the introduced solution. The pressure in the joint venture also increases in parallel.

The pressure in the EP becomes positive in late pregnancy due to the increase in intra-abdominal pressure (transmitted to the EP through the intervertebral foramen) and the expansion of the epidural veins. A decrease in EP volume promotes wider distribution of the local anesthetic.

An indisputable fact is that the drug introduced into the EP enters the CSF and CM. Less explored is the question - how does it get there? A number of guidelines on regional anesthesia describe the lateral spread of drugs injected into the EN with their subsequent diffusion through the cuffs of the spinal roots into the CSF (Cousins \u200b\u200bM., Bridenbaugh P., 1998).

This concept is logically justified by several facts. First, in the cuffs of the spinal roots there are arachnoid granulations (villi) similar to those in the brain. Through these villi, CSF is secreted into the subarachnoid space. Secondly, at the end of the 19th century. in the experimental studies of Key and Retzius, it was found that substances introduced into the SP of animals were later found in the EP. Third, it was found that red blood cells are removed from the CSF by passage through the same arachnoid villi. These three facts were logically combined, and it was concluded that drug molecules, the size of which is smaller than the size of erythrocytes, can also penetrate from the EP into the subarachnoid through the arachnoid villi. This conclusion, of course, is attractive, but it is false, built on speculative conclusions and not supported by any experimental or clinical research.

Meanwhile, with the help of experimental neurophysiological studies, it was found that the transport of any substances through the arachnoid villi is carried out by micropinocytosis and only in one direction - from the CSF outward (Yamashima T. et al., 1988, etc.). If this were not the case, then any molecule from the venous bloodstream (most of the villi are washed by the venous blood) could easily penetrate the CSF, thus bypassing the blood-brain barrier.

There is another widespread theory explaining the penetration of drugs from EP into CM. According to this theory, drugs with a high ability to dissolve in fats (or rather, the non-ionized forms of their molecules) diffuse through the wall of the radicular artery passing into the EP, and enter the CM with the blood flow. This mechanism also does not have any supporting data.

In experimental studies on animals, the rate of penetration into the CM of fentanyl introduced into the EP was studied with intact radicular arteries and after applying a clamp on the aorta, which blocks blood flow in these arteries (Bernards S., Sorkin L., 1994). There were no differences in the rate of penetration of fentanyl into the CM, however, there was a delayed elimination of fentanyl from the CM in the absence of blood flow through the radicular arteries. Thus, the radicular arteries play an important role only in the “washing out” of drugs from the CM. Nevertheless, the refuted "arterial" theory of drug transport from EP to CM continues to be mentioned in special guidelines.

Thus, at present, only one mechanism of drug penetration from EP into CSF \u200b\u200b/ CM has been experimentally confirmed - diffusion through the membranes of the CM (see above).

New data on the anatomy of the epidural space

Most of the early studies of the anatomy of EN was performed with the introduction of X-ray contrast solutions or at autopsy. In all these cases, the researchers faced a distortion of the normal anatomical relationships due to the displacement of the EP components relative to each other.

Interesting data have been obtained in recent years with the help of computed tomography and epiduroscopic technique, which makes it possible to study the functional anatomy of EN in direct connection with the technique of epidural anesthesia. For example, using computed tomography, it was confirmed that the spinal canal is oval above the lumbar spine, and triangular in the lower segments.

Using a 0.7 mm endoscope inserted through a Tuohy 16G needle, it was found that the volume of the EPO increases with deep breathing, which can facilitate catheterization (Igarashi, 1999). According to CT data, adipose tissue is mainly concentrated under the ligamentum flavum and in the area of \u200b\u200bthe intervertebral foramen. Fatty tissue is almost completely absent at the C7-Th1 levels, while the hard membrane is in direct contact with the yellow ligament. The fat of the epidural space is arranged in cells covered with a thin membrane. At the level of the thoracic segments, the fat is fixed to the canal wall only along the posterior midline, and in some cases loosely attached to the hard shell. This observation can partially explain the cases of asymmetric distribution of MA solutions.

In the absence of degenerative diseases of the spine, the intervertebral foramen are usually open, regardless of age, which allows the injected solutions to freely leave the EP.

Using magnetic resonance imaging, new data were obtained on the anatomy of the caudal (sacral) part of the EP. Calculations carried out on the bone skeleton indicated that its average volume is 30 ml (12-65 ml). Studies performed using MRI have taken into account the volume of tissue filling the caudal space and established that its true volume does not exceed 14.4 ml (9.5-26.6 ml) (Crighton, 1997). In the same study, it was confirmed that the dural sac ends at the level of the middle third of the S2 segment.

Inflammatory diseases and previous surgeries distort the normal anatomy of EN.

Subdural space

On the inner side, the arachnoid membrane is very close to the DM, which nevertheless does not connect with it. The space formed by these membranes is called subdural.

The term "subdural anesthesia" is incorrect and not identical to the term "subarachnoid anesthesia". Accidental injection of anesthetic between the arachnoid and the dura mater can cause inadequate spinal anesthesia.

Subarachnoid space

It starts from the foramen magnum (where it passes into the intracranial subarachnoid space) and continues approximately to the level of the second sacral segment, limited by the arachnoid and pia mater. It includes CM, spinal roots, and cerebrospinal fluid.

The width of the spinal canal is about 25 mm at the cervical level, at the chest level it narrows to 17 mm, at the lumbar (L1) it expands to 22 mm, and even lower to 27 mm. The anteroposterior dimension along the entire length is 15-16 mm.

Inside the spinal canal are the CM and cauda equina, CSF, as well as the blood vessels supplying the CM. The end of the CM (conus medullaris) is at the L1-2 level. Below the cone, the CM transforms into a bundle of nerve roots (cauda equina), freely “floating” in the CSF within the dural sac. Currently, it is recommended to puncture the subarachnoid space in the intervertebral space L3-4 to minimize the likelihood of injury from the CM needle. The cauda equina roots are quite mobile, and the risk of injury from the needle is extremely small.

Spinal cord

It is located from the foramen magnum to the upper edge of the second (very rarely third) lumbar vertebra. Its average length is 45 cm. In most people, CM ends at the L2 level, in rare cases reaching the lower edge of the 3rd lumbar vertebra.

Spinal cord blood supply

The SM is supplied with the spinal branches of the vertebral, deep cervical, intercostal and lumbar arteries. The anterior radicular arteries enter the spinal cord alternately - now on the right, then on the left (more often on the left). The posterior spinal arteries are upward and downward oriented extensions of the posterior radicular arteries. The branches of the posterior spinal arteries are connected by anastomoses with similar branches of the anterior spinal artery, forming numerous choroid plexus in the pia mater (pial vascular network).

The type of blood supply to the SM depends on the level of entry into the spinal canal of the largest radicular (radiculomedular) artery in diameter - the so-called Adamkevich artery. Various anatomical variants of the SM blood supply are possible, including one in which all segments below Th2-3 are fed from one Adamkevich artery (variant a, about 21% of all people).

In other cases, it is possible:

b) the lower additional radiculomedullary artery accompanying one of the lumbar or 1st sacral root,

c) the upper accessory artery accompanying one of the thoracic roots,

d) loose type of food SM (three or more anterior radiculomedullary arteries).

Both in variant a and in variant c, the lower half of the CM is supplied with only one Adamkevich artery. Damage to this artery, compression by an epidural hematoma or an epidural abscess can cause severe and irreversible neurological consequences.

From the CM, blood flows through the tortuous venous plexus, which is also located in the pia mater and consists of six longitudinally oriented vessels. This plexus communicates with the internal vertebral plexus of the EP, from which blood flows through the intervertebral veins into the systems of the azygos and semi-unpaired veins.

All venous system The EP has no valves, so it can serve as an additional system for the outflow of venous blood, for example, in pregnant women with aorto-caval compression. The overflow of blood to the epidural veins increases the risk of damage during puncture and catheterization of the epidural veins, including the likelihood of accidental intravascular injection of local anesthetics.

Cerebrospinal fluid

The spinal cord is washed by CSF, which plays a cushioning role to protect it from injury. CSF is a blood ultrafiltrate (clear, colorless liquid) that is formed by the choroidal plexus in the lateral, third, and fourth ventricles of the brain. The rate of CSF production is about 500 ml per day, so even the loss of its significant volume is quickly compensated.

CSF contains proteins and electrolytes (mainly Na + and Cl-) and at 37 ° C has a specific gravity of 1.003-1.009.

Arachnoid (pachyon) granulations located in the venous sinuses of the brain drain most of the CSF. The rate of absorption of CSF depends on the pressure in the CP. When this pressure exceeds the pressure in the venous sinus, thin tubes in the pachyon granulation open and allow CSF to enter the sinus. After the pressure is equalized, the lumen of the tubes closes. Thus, there is a slow circulation of CSF from the ventricles to the SC and further to the venous sinuses. A small part of CSF is absorbed by the veins of the joint venture and lymphatic vessels, therefore, some local circulation of CSF occurs in the vertebral subarachnoid space. CSF absorption is equivalent to CSF \u200b\u200bproduction, so the total volume of CSF is usually in the range of 130-150 ml.

Individual differences in CSF volume in the lumbosacral parts of the spinal canal are possible, which can affect the distribution of MA. Studies using NMR have revealed the variability of CSF volumes of the lumbosacral region in volumes from 42 to 81 ml (Carpenter R., 1998). It is interesting to note that overweight people have less CSF volume. There is a clear correlation between CSF volume and the effect of spinal anesthesia, in particular, the maximum prevalence of the block and the rate of its regression.

Spinal roots and spinal nerves

Each nerve is formed by connecting the anterior and posterior roots of the CM. The posterior roots have thickenings - the ganglia of the posterior roots, which contain the bodies of the nerve cells of the somatic and autonomic sensory nerves. The anterior and posterior roots separately pass laterally through the arachnoid and dura mater before joining at the level of the intervertebral foramen, forming the mixed spinal nerves. In total, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and one coccygeal.

CM grows more slowly than the spinal column, so it is shorter than the spine. As a result, the segments and vertebrae are not in the same horizontal plane. Since the CM segments are shorter than the corresponding vertebrae, the distance that must be covered gradually increases in the direction from the cervical segments to the sacral ones. spinal nerveto reach "your" intervertebral foramen. At the level of the sacrum, this distance is 10-12 cm. Therefore, the lower lumbar roots elongate and bend caudally, forming a cauda equina together with the sacral and coccygeal roots.

Within the subarachnoid space, the roots are covered only by a layer of the pia mater. This is in contrast to EP, where they become large mixed nerves with a significant amount of connective tissue both inside and outside the nerve. This circumstance explains that spinal anesthesia requires much lower doses of local anesthetic than epidural block.

Individual features of the spinal root anatomy can determine the variability of the effects of spinal and epidural anesthesia. The size of the nerve roots in different people can vary significantly. In particular, the spine diameter L5 can range from 2.3 to 7.7 mm. The posterior roots are larger than the anterior ones, but they consist of trabeculae, which can be easily separated from each other. Due to this, they have a larger surface of contact and greater permeability to local anesthetics in comparison with thin and non-trabecular anterior roots. These anatomical features partly explain the easier reaching of the sensory block compared to the motor block.