Go Human spinal cord cervical thoracic lumbar sacral coccyx spinal discs
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Human spine

The spine (spinal column) consists in an adult of 24 vertebrae (7 cervical, 12 thoracic, 5 lumbar), sacrum and tailbone. The sacrum consists of 5 intergrown sacral vertebrae, and the tailbone of 4-5 coccygeal (Fig. 1).

the structure of the human spine
Fig. 1. Spine (structure):
a - side view;
b - front view;
in - rear view.
1 - cervical;
2 - thoracic;
3 - lumbar;
4 - sacral section;
5 - coccyx.
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Each free vertebra in the spine consists of a more massive part located anteriorly, the vertebral body and the arc. When one vertebra is placed on another body, the vertebral arches form the spinal canal in which the spinal cord is located. The cuts on the arches of the vertebrae form intervertebral holes leading to the spinal canal. Paired transverse processes go from the arches of the vertebrae to the sides, up and down two pairs of articular processes, and from the middle one spinous process (Fig. 2).

vertebrae
Fig. 2. The eighth thoracic vertebra (right): 1 - spinous process; 2 - transverse process; 3 - rib facet of the transverse process; 4 - superior articular process: 5 - superior costal fossa; 6 - vertebral body; 7 - lower rib fossa; 8 - lower vertebral notch; 9 - lower articular process. Fig. 3. The first cervical vertebra (above): 1 - posterior tubercle; 2 - lateral mass; 3 - transverse process; 4 - superior articular fossa; 5 - anterior tubercle.

The size of the vertebrae increases from top to bottom to the upper sacral, and then decreases sharply. The cervical vertebrae have holes in the transverse processes through which the vertebral artery and vein pass. The body of the VI cervical vertebra has an anterior tubercle, developed more strongly than in other vertebrae (Schassegnac's tubercle). It is convenient to press the tubercle to the carotid artery when bleeding from it. The spinous process of the VII cervical vertebra is long, easily palpable in humans and is one of the identification points when counting vertebrae. The I of the cervical vertebra - Atlanta - has no body (Fig. 3). It has anterior and posterior arches with articular areas above and below for articulation with the occipital bone and II cervical vertebra. The II cervical vertebra - the axial or epistrophy - has a process directed upwards (the tooth), which joins with the I cervical vertebra. The bodies of the vertebrae (except I and II of the cervical) are connected to each other by means of cartilaginous intervertebral disks and ligaments .

The articular processes form the intervertebral joints . The spine has physiological (normal) curvatures: in the cervical region - a bend anteriorly (lordosis), in the thoracic - posteriorly (kyphosis), in the lumbar - again anteriorly. In the spine, flexion and extension, side bending and rotation are possible. The most mobile are the cervical and upper lumbar sections.

The spine (columna vertebralis - vertebral column) is the main part of the skeleton of the body, serves as a case for the spinal cord, an organ of support and movement.

Embryology In embryonic development of the spine, there are three stages: membranous, cartilaginous and bone. The change of stages occurs gradually, in the form of partial replacement and displacement of one tissue by another.

At an early stage of fetal development, mesenchymal cells accumulate around the resulting chord, which serve as an embryo of the vertebral bodies and ligamentous apparatus of the spine. In the 5-week embryo, the cells surrounding the chord are divided into intersegmental arteries into segments — sclerotomes (Fig. 1, a). Accordingly, the last are myotomes, of which the muscles develop. Each sclerotome is divided into two parts: caudal, more dense, and cranial, less dense. Subsequently, the sclerotome cells located near the arteries differentiate into the vertebra, and the intervertebral disc develops from the head portion of the caudal half of the sclerotome located far from the intersegmental arteries (Fig. 1, b). Myotom during embryogenesis is fixed to two adjacent vertebrae, which ensures the action of muscles on the spine (Fig. 1, c).

spinal development scheme
Fig. 1. Scheme of the development of the spine according to Kay and Compur; and each segment is divided by an intersegmental artery into two sections; b - areas adjacent to the artery, differentiated into the vertebra; the head part of the dense caudal half, located far from the intersegmental artery, is differentiated into the intervertebral disc, and in the pre-cartilage vertebral body: 1 - ectoderm, 2 - dermatitis; 3 - myotome; 4 — spinal nerve; 5 - chord; in - the primary vertebra, 7 - the aorta; 8 - head half of sclerotome, 9 - caudal half of sclerotome; 10 - intersegmental artery; 11 - the zone from which the intervertebral disc develops; 12 - zone, differentiating into the vertebra; 13 - body of the cartilage vertebra; 14 - extension of the chord in the intervertebral zone.

The formation of the intervertebral disc begins with the dorsal part, the most distant from the power source - the aorta. At the 10th week of embryonic development, the intervertebral disc is separated from the cartilage vertebra by a fibrocartilaginous membrane. By this time, the elements of the fibrous ring begin to form along the periphery of the intervertebral disk. In the 4-month embryo, the fibrous ring becomes more pronounced and binds the adjacent vertebrae firmly. Further, a relative decrease in the thickness of the intervertebral disk occurs, the fibrous ring expands in the central direction, but by the time of birth the intervertebral disk is not yet formed.


Fig. 2. The nuclei of ossification and the vertebral vessels of the fetus 3.5 months. (Fig. with enlightened drug; X15).


Fig. 3. II lumbar vertebra 6-month fetus; visible vessels of the nuclei of ossification (Fig. with enlightened drug; X15).

In the 10th week, the vertebrae become cartilaginous. The first points of ossification in the vertebrae appear at the 8–10th week of embryonic development. At the beginning of the 4th month of uterine life, they merge into one nucleus in the body of the vertebra and into two nuclei in the arch. The process of ossification of the vertebrae depends on their blood supply. Vessels always “go ahead” ossification (Fig. 2). The presence of two nuclei of ossification in the vertebral body can cause an abnormal development - the sagittal cleft of the vertebral body (rachishisis, see below), which is accompanied by other disorders of the normal formation of the spine with the formation of curvatures and deformations of it.

Further changes in the nuclei of ossification are reduced to an increase in their size and the 6-month embryo nucleus directly adjacent to the posterior surface of the body. The core height is somewhat less than the height of the vertebral body. The nuclei of the vertebra are built of radial bony columns, diverging from the vascular gate (Fig. 3). During the following months of embryonic development, an increase in the vertebra and a gradual replacement of the cartilage tissue of the bone occurs. At the same time, at the moment of birth of the child, the fusion of the nuclei of ossification does not yet occur. In the newborn, the transverse processes of the lateral nuclei of ossification are clearly visible, but the transverse process of the vertebra remains mostly cartilaginous. Other processes remain cartilaginous.

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During the uterine life, different parts of the spine grow in length with unequal energy. After birth, the lumbar spine grows most rapidly.

Anatomy . The human spine (Fig. 1) consists of 33–34 vertebrae, of which 24 are free (7 cervical, 12 thoracic and 5 lumbar); the rest (accreted) form two bones - the sacrum (5 vertebrae) and the tailbone (4-5 vertebrae). Each vertebra in the front has a body (corpus vertebrae), from which the arch (arcus vertebrae) departs posteriorly, carrying a series of processes (Fig. 5). The handle together with the posterior surface of the vertebral body limits the spinal foramen (foramen vertebrale). The vertebral foramina of all vertebrae form a vertebral canal (canalis vertebralis), in which the spinal cord with shells and vessels lies. In the arch distinguish the thickened anterior section - the legs (pediculi arcus vertebrae) and the plate (lamina arcus vertebrae). Transverse processes (processus transversi) depart from the arch to the sides, posterior process - spinous process (processus spinosus), up and down - articular processes (processus articulares sup. Et inf.).

thoracic and lumbar vertebrae
Fig. 5. Typical thoracic and lumbar vertebrae; a - VIII thoracic vertebra: 1 - processus spinosus; 2 - proc. transversus; 3 - fovea costalis transversalis; 4 - proc. articularis sup .; 5 - fovea costalis sup .; 6 - corpus vertebrae; 6 - III lumbar vertebra: 1 - proc. spinosus; 2 and 3 - proc. articularis sup .; 4 - incisure vertebralis sup .; 5 - corpus vertebrae; 6 - incisura vertebralis inf .; 7 - proc. transversus; 8 - proc. articularis inf.

I cervical vertebra
Fig. 6. I cervical vertebra (above): 1 - tuberculum post .; 2 - massa lat .; 3 - proc. transversus; 4 - fovea articularis sup .; 5 - tuberculum ant.

II cervical vertebra
Fig. 6a. II cervical vertebra (A - from above, B - from the side): 1 and 8 - proc. spinosus; 2 - proc. transversus, 3 - facies articularis sup .; 4 - dens; 5 = corpus vertebrae; 6 - foramen transversarium, 7 - proc. articularis inf. Fig. 4. Spine: A - side view; B - front view; B - view from behind. 1 - cervical; 2 - thoracic; 3 - lumbar; 4 - sacral section; I - coccyx.

I and II cervical vertebrae differ from the general type of vertebral structure. I vertebra - atlas (atlas) is a ring consisting of two arcs interconnected by side thickened parts (Fig. 6). The II cervical vertebra - the epistrophy, or axial (axis), has a dentlike process (dens) on the upper surface of the body, which articulates with the anterior arch of the I cervical vertebra (Fig. 6a).

The bodies of the vertebrae are interconnected and with the sacrum through intervertebral discs (disci intervertebrales). The latter consist of a fibrous ring (anulus fibrosus) and a gelatinous nucleus (nucleus pulposus), which is a closed cavity with gelatinous, vitreous contents.

Intervertebral discs (Fig. 7) make up 20–25% of the length of the spinal column in an adult. In the segments of the spine, where its mobility is more pronounced (lumbar, cervical), the height of the disks is greater. Due to its elasticity, the intervertebral disk absorbs shocks that the spine experiences. The height of the intervertebral disc and spinal column is, in fact, variable and depends on the dynamic equilibrium of oppositely directed forces. After a night's rest, the height of the disk increases, and by the end of the day decreases; the daily variation in the length of the spine reaches 2 cm.

intervertebral disc diagram
Fig. 7. Intervertebral disk (diagram): 1 - end cartilage plate; 2 - apophysis of the vertebral body; 3 - gelatinous nucleus; 4 - fibrous ring.

Anterior and posterior longitudinal ligaments (ligg. Longitudinalia anterius et posterius) run along the anterior and posterior surfaces of the vertebral bodies and disks. The anterior longitudinal ligament stretches from the occipital bone to the sacrum, attaching to the vertebral bodies. This bundle has great elastic strength. The posterior longitudinal ligament also starts from the occipital bone and reaches the sacral canal, but does not attach to the vertebral bodies, but firmly fuses with the discs, forming extensions in these places (Fig. 8 and 9).


Fig. 8. Ligaments and joints of the thoracic spine: 1 and 5 - lig. costotransversarium post .; 2 - lig. intercostale int .; 3 - lig. tuberculi costae; 4 - lig. intertransversarium; 6 - capsula articularis; 7 and 8 - lig. supraspinale.


Fig. 9. Lumbar spine: 1 - lig. longitud. post .; 2 - lig. flavum; h - lig. interspinale; 4 - lig. supraspinale; 5 - proc. artic. sup. 6 - proc. transversus. 7 - lig. inter-transversarium; 8 - lig. longitud. ant .; 9 - anulus tibrosus; 10 - nucl. pulposus.

The arms of the vertebrae are interconnected by means of the yellow ligaments (ligg. Flava), the spinous processes - by the interosseous ligaments (ligg. Interspinalia), the transverse processes - by the intertransversal ligaments (ligg. Intertransversaria). Above the spinous processes along the entire length of the spinal column is the supraspinal ligament (lig. Supraspinale), which increases in the cervical region in the sagittal direction and is called the nuchal ligament (lig. Nuchae). Articular processes form intervertebral joints (articulationes intervertebrales). In different parts of the spinal articular processes have different shape and location. So, in the thoracic region they are located frontally. The articular surface of the upper processes is directed posteriorly, the lower - anteriorly. Therefore, the gap between the processes on a direct radiograph is not visible, and on the side is well detected. The articular processes of the lumbar vertebrae occupy a sagittal position, and therefore the gap between them on a direct radiograph is clearly visible.

types of posture
Fig. 10. Types of posture: a - normal posture; b - flat back; in - round or round-concave back; d - slouching back.

In the process of development of the child, the spine acquires several curves in the sagittal plane: in the cervical and lumbar regions it bends forward — lords are formed (see), in the thoracic and sacral parts — back — kyphosis is formed (see). These curves, along with the elastic properties of the intervertebral discs, determine the damping characteristics of the spine.

Under the influence of a number of adverse conditions - weakness of the musculo-ligamentous apparatus of the spine, static disorders (incorrect posture of a child during school and home classes) - an abnormal (pathological) posture develops (Fig. 10). When smoothing the bends of the spine, a flat back develops, with an increase in them - round or round-concave. The most complex in nature are violations of posture due to lateral curvatures of the spine, forming a scoliotic posture. However, it should not be confused with scoliosis (see) - a disease that also manifests itself as a lateral curvature of the spine, but differs in the deformation of individual vertebrae and the spine as a whole.

The movements of the spine can occur around three axes: transverse (flexion and extension), sagittal (tilt to the sides) and vertical (circular movements). The most mobile are the cervical and lumbar spine, the upper and lower segments of the thoracic region are smaller, and the middle segment of it is even smaller.

The degree and nature of spinal mobility is associated with a number of conditions, in particular with the shape and position of the articular processes, the height of the intervertebral discs, the presence of ribs that restrict the movement of the thoracic spine.

The blood supply of the spine is carried out from large arteries, passing either directly on the bodies of the vertebrae, or near them, and these vessels depart directly from the aorta or (for the cervical spine) from the subclavian artery. The blood in the spine comes under great pressure, which causes a high degree of blood supply, even small branches.

The lumbar and intercostal arteries (aa. Lumbales et intercostales) run along the anterior-lateral surface of the vertebral bodies in the transverse direction, and in the region of the intervertebral foramen there are posterior branches that supply the dorsal vertebrae and soft tissues of the back. The posterior branches of the lumbar and intercostal arteries give spinal arteries (rami spinales), penetrating the spinal canal. In the spinal canal, the main trunk of the spinal artery is divided into anterior (larger) and posterior branches. The latter passes transversely along the posterolateral wall of the spinal canal and anastomoses with the corresponding artery of the opposite side. The anterior end branch of the spinal artery runs transversely anteriorly and anastomoses on the posterior surface of the vertebral body with a similar branch of the opposite side. These branches are involved in the formation of the anastomotic network located on the posterior surface of the vertebral bodies in the posterior longitudinal ligament. Anastomotic network stretches along the entire spinal canal and has longitudinal and transverse branches. The arteries, the feeding bodies of the vertebrae, the spinal cord, and the peripheral part of the intervertebral disk depart from it.

Through the front and side surfaces of the vertebral bodies, a large number of branches enter, among which there are 2-3 large branches entering the body near the midline. These branches anastomose in the body of the vertebra with the posterior branches. Vessels do not pass from the vertebral body into the intervertebral disk.

The venous system of the spine is represented by four venous plexuses: two external (plexus venosi vertebrales externi), located on the front surface of the vertebral bodies and behind the arches, and two internal (plexus venosi vertebrales interni). The largest plexus, the anterior intravertebral, is represented by large vertical trunks connected by transverse branches; This plexus is located on the posterior surface of the vertebral bodies and is fixed to their periosteum with numerous jumpers. The posterior intravertebral plexus does not have strong bonds with the walls of the spinal canal and therefore is easily displaced. All four venous plexuses of the spine have numerous connections between each other, with the anterior and external anterior plexuses anastomosing by vv. basivertebrales, which pass through the vertebral bodies, and the posterior external and internal plexuses are connected by thin branches piercing the yellow ligaments.

The outflow of venous blood from the spine is carried out in the system of the upper and lower vena cava along the vertebral, intercostal, lumbar and sacral veins. Each intervertebral vein, passing from the spinal canal through the corresponding intervertebral foramen, is firmly connected to the periosteum of the bone edges of the openings, and therefore, when damaged, these veins do not collapse.

The venous plexuses of the spine, forming a single whole, extend from the base of the skull (here they are associated with the occipital venous sinus) to the coccyx. This venous system, widely anastomosing with paravertebral veins, is an important communication between the inferior and inferior vena cava. This collateral path is believed to be of great importance in maintaining the functional balance between the systems of the upper and lower vena cava. The absence of valves in the spinal veins makes it possible for blood to move in any direction. This functional feature of the vertebral veins, according to some authors, explains their role in the spread of infection and metastases in the spine.

Lymphatic drainage in the cervical spine is in the direction of the deep lymph nodes of the neck; in the upper chest, in the nodes of the posterior mediastinum; in the lower thorax - through the intercostal lymph nodes in the thoracic duct. From the lumbar and sacral spine lymph is collected in the same lymph nodes.

Postnatal development . In the postnatal development of the spine, growth and ossification of the vertebrae continue, and differentiation of the intervertebral discs occurs. In the first year of life, the restructuring of the spongy bone of the vertebral body occurs. According to most authors, synostosis of the nuclei of ossification in the area of ​​the base of the spinous process occurs by three years, but in some cases this process is delayed to 12-13 years, and sometimes it does not end at all; so spina bifida arises (see). This is often observed in the V lumbar and I sacral vertebrae. The frequency of spina bifida in these vertebrae prompted her to consider it not as an abnormal development of the spine, but as its variant.

The fusion of the nucleus of ossification of the vertebral body with the nuclei of ossification of the arch in the lumbar region occurs at the age of 4-8 years. In the thoracic region, a layer of cartilage between them lasts up to 12 years.


Fig. 11. The distribution of forces acting on the intervertebral disk

In the process of postnatal development of the intervertebral disc, the gelatinous nucleus gradually condenses and the fibrous ring fibrous structures differentiate. In young subjects, the gelatinous core contains a mainly water-rich basic amorphous substance located among the collagen fibers. The saturation of the gelatinous nucleus with water determines its physical properties as a static shock absorber. loads that distribute mechanical forces over the entire surface of the vertebral body (Fig. 11). With age, due to a decrease in the water content, the turgor of the nucleus decreases, it gradually condenses and loses its elasticity. In people over 50, the gelatinous core resembles a caseous mass.

The fibrous ring in the process of postnatal development also undergoes a number of changes. Already at 2 years of age, there is marked fibrousness in the anterior and posterior sections of the disk with interlacing beams. With age, interlacing of fibers becomes more difficult, they swell. This is especially clearly revealed in the second five years of life. By the end of the second decade, the swelling is significant, and the fibers are not very clear. The intervertebral disc as a whole finishes its development by 22-24 years.