Spinal cord

The spinal cord (medulla spinalis) in appearance is a long, cylindrical shape, flattened from front to back of the sternum. In this regard, the transverse diameter of the spinal cord is greater than the anteroposterior diameter.

The spinal cord is located in the vertebral canal and at the level of the lower edge of the large occipital orifice passes into the brain. In this place, from the spinal cord (its upper boundary), the roots, forming the right and left spinal nerves, come out. The lower border of the spinal cord corresponds to the level of I-II lumbar vertebrae. Below this level, the tip of the cerebral cone of the spinal cord continues into the thin terminal (terminal) filament. The filum terminale in its upper parts still contains a nerve tissue and is a rudiment of the caudal end of the spinal cord. This part of the end thread, called internal, is surrounded by the roots of the lumbar and sacral spinal nerves and, together with them, is in a blindly terminating sac formed by the hard shell of the spinal cord. In an adult, the inner part of the end thread has a length of about 15 cm. Below the level II of the sacral vertebra, the terminal filament is a connective tissue formation that is the continuation of all three shells of the spinal cord and is called the outer end of the end thread. The length of this part is about 8 cm. It ends at the level of the body II of the coccygeal vertebra, fused with its periosteum.

The length of the spinal cord in an average person is 43 cm (for men - 45 cm, for women - 41-42 cm), weight - about 34-38 g, which is about 2% of the brain mass.

In the cervical and lumbosacral divisions of the spinal cord, two noticeable thickening are found: cervical thickening (intumescentia cervicalis) and lumbosacral thickening (intumescentia lumbosacralis). The formation of thickenings is explained by the innervation of the upper and lower extremities respectively from the cervical and lumbosacral spinal cord. In these departments in the spinal cord there is more than in other departments, the number of nerve cells and fibers. In the lower parts, the spinal cord gradually narrows and forms a cone medullaris.

On the anterior surface of the spinal cord, the anterior median aperture (fissura medidna anterior) is visible, which extends deeper into the tissue of the spinal cord than the posterior median sulcus (sulcus medianus posterior). They are the boundaries separating the spinal cord into two symmetrical halves. In the depth of the posterior median furrow there is a glial posterior median septum (septum medianum posterius) that penetrates almost into the entire thickness of the white matter . This septum reaches the posterior surface of the gray matter of the spinal cord.

On the anterior surface of the spinal cord, on either side of the anterior slit, the anterior lateral groove passes (sulcus anterolateralis). It is the site of the exit from the spinal cord of the anterior (motor) roots of the spinal nerves and the boundary on the surface of the spinal cord between the anterior and lateral cords. On the back surface, on each half of the spinal cord there is a posterior lateral groove (sulcus posterolateralis) - the site of penetration into the spinal cord of the posterior sensory roots of the spinal nerves. This furrow serves as a boundary between the lateral and posterior cords.

The front root (radix anterior) consists of the appendages of the motor (motor) nerve cells located in the anterior horn of the gray matter of the spinal cord. The posterior root (radix posterior) is sensitive, it is represented by a set of pseudo-unipolar cells penetrating the spinal cord, whose bodies form a spinal cord (ganglion spinale), lying in the vertebral canal at the junction of the posterior root with the anterior. Throughout the entire spinal cord, 31-33 pairs of roots leave each side of the spinal cord. The anterior and posterior roots near the inner edge of the intervertebral foramen converge, merge with each other and form a spinal nerve (nervus spinalis).

Thus, 31-33 pairs of spinal nerves are formed from the roots. The portion of the spinal cord corresponding to two pairs of rootlets (the two anterior and two posterior ones) is called the segment. Accordingly, 31-33 pairs of spinal nerves in the spinal cord are isolated by 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal segments. Each segment of the spinal cord corresponds to a specific area of the body that receives innervation from this segment. Mark the segments with the initial letters pointing to the region (part) of the spinal cord, and the numbers corresponding to the ordinal number of the segment:

• cervical segments (segmenta cervicalia) - CI-CVIII;
• thoracic segments (segmenta thoracica) - ThI-ThXII;
• lumbar segments (segmenta lumbalia) - LI-LV;
• sacral segments (segmenta sacralia) - SI-SV;
• coccygeal segments (segmenta coccygea) - CoI-CoIII.

It is very important for a doctor to know the topographic relationships of segments of the spinal cord with the vertebral column (skeleotopia segments). The length of the spinal cord is much smaller than the length of the spine. Therefore, the serial number of any segment of the spinal cord and the level of its position, starting with the lower cervical segment, do not correspond to the ordinal number of the vertebra. The positions of the segments with respect to the vertebrae can be determined as follows. The upper cervical segments are located at the level corresponding to their ordinal number of vertebral bodies. The upper thoracic segments lie one vertebra higher than the bodies of the corresponding vertebrae. In the middle thoracic region, this difference between the corresponding segment of the spinal cord increases by 2 vertebrae, in the lower thoracic segment by 3. The lumbar segments of the spinal cord lie in the vertebral canal at the level of the X and XI thoracic vertebrae, the sacral and coccygeal segments at the level of the XII thoracic and I of the lumbar vertebrae.

The spinal cord consists of nerve cells and fibers of gray matter, which in the transverse section have the form of the letter H or butterflies with straightened wings. On the periphery of the gray matter is a white substance formed only by nerve fibers.

In the gray matter of the spinal cord, there is a central canal (canalis centralis). It is the remainder of the cavity of the neural tube and contains spinal or cerebrospinal fluid. The upper end of the canal communicates with the IV ventricle of the brain, and the lower, somewhat expanding, forms a blindly terminating small ventriculus terminalis. The walls of the central canal of the spinal cord are lined with ependyma, around which is the central gelatinosa centralis. Ependyma is a dense layer of epepidymocytes (cells of neuroglia) that perform a demarcation and support function. On the surface facing the cavity of the central channel, there are numerous cilia that can contribute to the current of cerebrospinal fluid in the canal. Inside the brain tissue from ependymocytes, thin long branching processes that perform a supporting function depart. In a person's adult, the central canal in different parts of the spinal cord, and sometimes all the way, grows.

The gray matter (substantia gnsea) forms symmetrical gray columns (columnae griseae) along the spinal cord to the right and left of the central channel. Ahead and back of the central canal of the spinal cord, these pillars are connected to each other by thin plates of gray matter, called the anterior and posterior gray adhesions.

In each column of gray matter, the front part is distinguished - the front column (columna ventralis, s. Anterior), and the posterior part - the posterior column (columna dorsalis, S. Posterior). At the level of the lower cervical, all thoracic and two upper lumbar segments (from СVII to LI-LII) of the spinal cord, the gray matter on each side forms a lateral protrusion - the lateral column (columna lateralis). In the other parts of the spinal cord (above the cervical VIII and below the II lumbar segments) there are no lateral columns.

On the transverse section of the spinal cord, the pillars of gray matter on each side have the form of horns. A wider front horn (cornu ventrale, s.anterius), and a narrow rear horn (cornu dorsale, S. Posterius), corresponding to the anterior and posterior posts, are distinguished. The lateral horn (cornu laterale) corresponds to the lateral intermediate (autonomous) column of the gray matter of the spinal cord.

In the anterior horns there are large nerve root cells - motor (efferent) neurons. These neurons form 5 nuclei: two lateral (anterior and posterolateral) two medial (anterior and posterior medial) and a central nucleus. The horn of the spinal cord is represented mainly by smaller cells. In the composition of the posterior, or sensitive, roots are the central processes of pseudo-unipolar cells located in the spinal (sensory) nodes.

The gray matter of the posterior horns of the spinal cord is not uniform. The bulk of the nerve cells of the horn form its own nucleus. In the white matter directly adjacent to the top of the rear horn of gray matter, a border zone is distinguished. Ahead of the latter there is a spongy zone, which was named in connection with the presence in this department of a large-globular glial network containing nerve cells. Even more anteriorly, a gelatinous substance (substantia galatinosa) is formed, consisting of small nerve cells. The processes of the nerve cells of the gelatinous substance, the spongy zone and the diffusely scattered beam cells in the whole gray matter, make a connection with the neighboring segments. As a rule, these processes terminate in synapses with neurons located in the anterior horns of their segment, as well as above and below segments. Starting from the horns of the gray matter to the anterior horns, the processes of these cells are located along the periphery of the gray matter, forming a narrow border of white matter near it. These bundles of nerve fibers are called front, lateral and posterior fasciae (fasciculi proprii ventrales, S. Anteriores, laterales et dorsales, S. Posteriores). The cells of all cores of the horn of the gray matter are, as a rule, intercalary (or conductor) neurons. The neurites that depart from the nerve cells, the totality of which forms the central and thoracic nuclei of the horns, are guided in the white matter of the spinal cord to the brain.

In the medial part of the base of the lateral horn, the thoracic nucleus (nucleus thoracicus), which is well defined by a layer of white matter , consists of large nerve cells. This nucleus extends along the entire posterior column of gray matter in the form of a cellular strand (the Clark nucleus). The largest diameter of this nucleus is at the level of XI thoracic to I lumbar segment.

The intermediate zone of the gray substance of the spinal cord is located between the anterior and posterior horns. Here, from the VIII cervical to the II lumbar segment, there is a protuberance of gray matter - the lateral horn. In the lateral horns there are centers of the sympathetic part of the autonomic nervous system in the form of several groups of small nerve cells combined into a lateral intermediate substance (substantia (grisea) intermedia lateralis]. The axons of these cells pass through the anterior horn and come out of the spinal cord as part of the anterior roots.

In the intermediate zone there is a central intermediate substance [substantia (grisea) intermedia centralis], the processes of the cells of which are involved in the formation of the spinal-cerebellar pathway. At the level of the cervical segments of the spinal cord between the anterior and posterior horns, and at the level of the upper thoracic segments - between the lateral and posterior horns in the white matter adjoining the gray, is the reticular formation (formatio reticularis). Here it has the form of thin rails of gray matter intersecting in different directions, and consists of nerve cells with a large number of processes.

The gray matter of the spinal cord with the posterior and anterior roots of the spinal nerves and its own beams of white matter bordering the gray matter form their own, or segmental, apparatus of the spinal cord. The main purpose of the segmentary apparatus as phylogenetically the oldest part of the spinal cord is the implementation of congenital reactions (reflexes) in response to stimulation (internal or external). IPPalov defined this type of activity of the segmental apparatus of the spinal cord with the term "unconditioned reflexes".

The white matter (substantia alba), as noted, is located outside of the gray matter. Furrows of the spinal cord divide the white matter into symmetrically arranged right and left three cord. The anterior funiculus (funiculus ventralis anterior) is located between the anterior median slit and the anterior lateral groove. In the white matter, a front white solder (commissura alba), which connects the anterior cords of the right and left sides, is seen posteriorly from the anterior median slit . The posterior funiculus (funiculus dorsalis, S. Posterior) lies between the posterior median and lateral furrows. Lateral funiculus (funiculus lateralis) is a white matter area between the anterior and posterior lateral grooves.

The white matter of the spinal cord is represented by the processes of nerve cells. The totality of these processes in the cords of the spinal cord is made up of three systems of fascicles (tracts or pathways) of the spinal cord:

1. short bundles of associative fibers connecting the segments of the spinal cord located at different levels;
2. in the efferent (afferent, sensitive) bundles, going to the centers of the cerebrum and the cerebellum;
3. descending (efferent, motor) bundles, coming from the brain to the cells of the anterior horns of the spinal cord.

The two last beam systems form a new (in contrast to the phylogenetically older segmented apparatus) over-segment conductor apparatus of bilateral connections of the spinal cord and brain. In the white substance of the anterior cords there are mainly downward conducting paths, in the lateral cords there are ascending and descending conducting paths, in the rear cords there are ascending conducting paths.

The front cord includes the following conductive paths:

1. Anterior cortical-spinal (pyramidal) pathway [tractus corticospinalis (pyramidalis) ventralis, s. Anterior] motor, generates sprouts of giant pyramidal cells (giant-pyramidal neurocytes). The bundles of nerve fibers that form this path lie near the anterior median slit, occupying the anterior medial divisions of the anterior cord. The conducting path transmits the impulses of motor reactions from the cortex of the cerebral hemispheres to the anterior horns of the spinal cord.

1. The reticular-spinal tract (tractus reticulospinalis) conducts impulses from the reticular formation of the brain to the motor nuclei of the anterior horns of the spinal cord. It is located in the central part of the anterior cord, lateral to the cortical and spinal path.
2. The anterior dorsal-thalamic path (tractus spinothalamicus ventralis, s. Anterior) lies somewhat anterior to the reticular-spinal path. Conducts impulses of tactile sensitivity (touch and pressure).
3. The ligament-spinal tract (tractus tectospinalis) connects the subcortical centers of vision (the upper hills of the roof of the midbrain) and the rumor (lower hills) with the motor nuclei of the anterior horns of the spinal cord. It is located medial to the anterior cortical-spinal (pyramidal) pathway. A bundle of these fibers directly adjoins the anterior median slit. The presence of such a path makes it possible to carry out reflex defensive movements with visual and auditory stimuli.
4. Between the anterior cortical-spinal (pyramidal) pathway in front and the anterior gray spike on the posterior there is a posterior longitudinal fasciculus (fasciculus longitudinalis dorsalis, S. Posterior). This bundle extends from the brainstem to the upper segments of the spinal cord. The fibers of the bundle conduct nerve impulses, coordinating, in particular, the work of the muscles of the eyeball and the muscles of the neck.
5. The pre-spinal cord (tractus vestibulospinalis) is located on the border of the anterior cord with the lateral. This pathway is localized in the surface layers of white matter of the anterior cord of the spinal cord, directly near its anterior lateral groove. The fibers of this pathway come from the vestibular nuclei of the VIII pair of cranial nerves located in the medulla oblongata, to the motor cells of the anterior horns of the spinal cord.

The lateral cord (funiculus lateralis) of the spinal cord contains the following pathways:

1. 1. The posterior spinal path (tractus spinocerebellaris dorsalis, S. Posterior, Flechsig's bundle) impulses of proprioceptive sensitivity, occupies the posterolateral sections of the lateral cord, near the posterior lateral sulcus. Medially, the fiber bundle of this conducting path lies in the lateral cortical-spinal and lateral spinal-thalamic pathways. In front of the fascicles of the posterior spinal cord path are in contact with the bundles of the same anterior path.
2. The anterior spinal cord pathway (tractus spinocerebellaris ventralis, s. Anterior, Hover's bundle), also bearing proprioceptive impulses in the cerebellum, is located in the anterolateral sections of the lateral cord. Ahead adjoins the anterior lateral groove of the spinal cord, bordering on the olive-spinal cord. Medially, the anterior spinal cord pathway belongs to the lateral spinal-thalamic and spin-cover tracts.
3. The lateral dorsal-thalamic tract (tractus spinothalamicus lateralis) is located in the anterior parts of the lateral cord, between the anterior and posterior spinal-cerebellar pathways - from the lateral side, the red-nucleus spinal and the pre-spinal cord, from the medial side. It imparts impulses of pain and temperature sensitivity.

Downward systems of lateral cord fibers include lateral cortical-spinal (pyramidal) and red-nuclear-spinal (extrapyramidal) pathways.

1. The lateral cortical-spinal cord pathways (tractus corticospinalis (pyramidalis) lateralis] conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord.The bundle of fibers of this path, which are the processes of giant pyramidal cells, is medial to the posterior spinal-cerebellar path and occupies a significant part of the area of the lateral cord, especially in the upper segments of the spinal cord.In the lower segments, it occupies an ever smaller and smaller area on the slices.In the front of this path is the red nuclear-spinal conducting th path.
2. The cerebro-spinal cord (tractus rubrospinalis) is located anterior to the lateral cortical-spinal (pyramidal) pathway. Lateral to it in a narrow area are the posterior spinal-cerebellar path (its anterior sections) and the lateral dorsal-thalamic path. The cerebro-spinal cord is a conductor of the pulses of automatic (subconscious) control of the movements and tone of the skeletal muscles to the anterior horns of the spinal cord.

In the lateral cords of the spinal cord, there are also bundles of nerve fibers that form other conductive pathways (for example, spinal cord, olive-spinal cord, etc.).

The posterior funiculus (funiculus dorsalis, S. Posterior) is divided into two fascicles at the level of the cervical and upper thoracic segments of the spinal cord by the posterior intermediate groove. The medial is directly attached to the posterior longitudinal groove - it is a thin fasciculus (fasciculus gracilis, Gaul's bundle). Lateral to it is a wedge-shaped fasciculus (fasciculus cuneatus, bunda Burdacha), adjoining from the medial side to the posterior horn. A thin bundle consists of longer conductors extending from the lower parts of the trunk and lower limbs of the corresponding side to the medulla oblongata. It includes fibers that enter into the composition of the posterior roots of the 19 lower segments of the spinal cord and occupy the more medial part of the posterior cord. Due to the entry into the 12 upper segments of the spinal cord of the fibers belonging to the neurons innervating the upper limbs and the upper part of the trunk, a wedge-shaped bundle is formed that occupies the lateral position in the posterior cord of the spinal cord. Thin and wedge-shaped bundles are bunches of proprioceptive sensitivity (joint-muscular feeling) that carry information about the position of the body and its parts in space into the cerebral cortex.

In different parts of the spinal cord, the proportions of the areas (on horizontal slices) occupied by gray and white matter are not the same. Thus, in the lower segments, in particular, in the region of the lumbar thickening, the gray matter on the cut takes the most part. Changes in the quantitative ratios of gray and white matter are explained by the fact that in the lower parts of the spinal cord the number of fibers of the descending pathways from the brain is significantly reduced, and only ascending routes are beginning to form. The number of fibers forming the ascending paths gradually increases from the lower segments to the upper ones. In transverse sections of the middle thoracic and upper cervical segments of the spinal cord, the area of the white matter is larger. In the area of the cervical and lumbar thickenings, the area occupied by the gray matter is larger than in other parts of the spinal cord.

The spinal cord of the newborn has a length of 14 cm (13.6-14.8 cm). The lower border of the brain is at the level of the lower edge of the II lumbar vertebra. By the age of two, the length of the spinal cord reaches 20 cm, and by 10 years, compared to the period of the newborn, it doubles. The thoracic segments of the spinal cord grow most rapidly. The mass of the newborn's spinal cord is about 5.5 g, in children 1 year - 10 g. By 3 years the mass of the spinal cord exceeds 13 g, and at 7 years is approximately 19 g.

In the transverse section, the spinal cord looks the same as an adult. In a newborn, the cervical and lumbar thickening is well expressed, the central channel is wider than in the adult. The decrease in the lumen of the central canal occurs mainly during 1-2 years, as well as in later age periods, when the mass of gray and white matter increases. The white matter increases more rapidly, especially at the expense of its own bundles of the segmental apparatus, which is formed earlier than the conducting paths connecting the spinal cord to the brain.

Blood vessels of the spinal cord. To the spinal cord there are branches from the vertebral artery (from the subclavian artery), deep cervical artery (from the rib-cervical trunk), and also from the posterior intercostal lumbar and lateral sacral arteries. Three long longitudinal arterial vessels adjoin it: the anterior and two posterior spinal arteries.

The anterior spinal artery (unpaired) abuts the anterior longitudinal slot of the spinal cord. It is formed from two analogous arteries (branches of the right and left vertebral arteries) in the upper parts of the spinal cord. The posterior spinal artery is paired. Each of the arteries is attached to the posterior surface of the spinal cord near the entry of the spinal roots of the spinal nerves into the brain. These 3 arteries continue to the lower end of the spinal cord. The anterior and the two posterior spinal arteries join together on the surface of the spinal cord with numerous anastomoses and with the branches of the intercostal, lumbar and lateral sacral arteries penetrating the vertebral canal through the intervertebral foramens and sending thin branches into the brain substance.

The veins of the spinal cord flow into the inner vertebral venous space.

[1], [2], [3], [4], [5]