Spinal nerves

Spinal nerves (n. Spinales) are paired, located metamerically nerve trunks. In a person 31-33 pairs of spinal nerves: 8 pairs of cervical, 12 pairs of pectoral, 5 pairs of lumbar, 5 pairs of sacral and 1-3 pairs of coccygeal, corresponding to 31-33 segments of the spinal cord. Each spinal nerve, according to its origin, corresponds to a certain segment of the body and innervates the skin segment (derivative of the dermatome) that developed from this segment, the muscles (from the myotoma) and the bones (from the sclerotome).

The spinal nerve begins with the motor and sensitive roots. The anterior (motor) spine (radix ventralis, s. Anterior, s. Motoria) of the spinal nerve is formed by axons of motor neurons whose bodies are in the anterior horns of the spinal cord. The posterior (sensitive) spine (radix dorsalis, S. Posterior, S. Sensoria) is formed by the central processes of pseudo-unipolar cells, the bodies of which form a spinal node. Peripheral processes of pseudo-unipolar neurons go to the periphery, where in organs and tissues are their receptors - receptors. The level of the exit of roots from the spinal cord does not coincide with the location of the intervertebral openings, since the spinal cord does not fill the entire vertebral canal. Roots, starting from the lower cervical, go to their intervertebral foramens in the descending direction. The roots of the lower lumbar and sacral spinal nerves form a "pony tail".

Each posterior root has an extension - the spinal node (ganglion spinale). The number of neurons forming the spinal cord is very large. In the cervical and lumbar spinal nodes there are about 50,000 nerve cells, in the pectoral nodes - 25,000, in the sacral nodes - 35,000 neurons in one node. There are spinal nodes near the intervertebral foramen. The spinal cord of the first and second cervical spinal nerves are respectively higher and lower than the atlas's arc. Each spinal node is surrounded by a connective tissue capsule. From the capsule to the parenchyma of the node, thin bundles of connective tissue fibers penetrate, which form the framework of the node and contain blood vessels. Neurons in the spinal nodes are arranged in groups, occupying mainly the periphery of the node. The center of the spinal cord consists mainly of the processes of nerve cells. Neurons of the node are surrounded by glial cells - mantle gliocytes.

At the exit through the intervertebral foramen from the vertebral canal, the anterior and posterior roots are joined, forming the spinal nerve trunk. It is short (0.5-1.5 cm long) and does not completely fill the intervertebral foramen, leaving space for passage of blood vessels. Each spinal nerve contains both motor and sensitive fibers. In the composition of the anterior roots, coming out of the VIII cervical, all the thoracic and upper two lumbar segments, there are always vegetative (sympathetic) preganglionic fibers coming from the neurons of the lateral horns of the spinal cord.

The spinal nerve, after exiting from the intervertebral foramen, is divided into several branches: the anterior, posterior, menin-heal, and also the white connective branch (in the thoracolumbar region). White connective branch is only with VIII cervical in II lumbar spinal nerves. The anterior and posterior branches of the spinal nerves are mixed. White connective branches contain preganglionic sympathetic fibers reaching the nodes of the sympathetic trunk.

The meningeal branches of the spinal nerves also penetrate through the corresponding intervertebral openings in the vertebral canal; innervate the walls of the spinal canal, the membranes of the spinal cord.

To all spinal nerves from the sympathetic trunk, gray connective branches (r. Communicantes grisei) pass. They are represented by sympathetic nerve fibers coming from all nodes of the sympathetic trunk. In the composition of all spinal nerves and their branches postganglionic sympathetic fibers are directed to the blood and lymphatic vessels, the skin, skeletal muscles and other tissues, which ensures their functions and metabolic processes (trophic innervation).

The posterior branches of the spinal nerves (r. Dorsales, S. Posteriores) give lateral and medial branches (r. Laterales and mediales), which innervate the deep (own) muscles of the back, the muscles of the occiput and the skin of the posterior surface of the head and trunk. Separating from the spinal nerves, the posterior branches go back (between the transverse processes of the vertebrae), bending around the articular processes. The posterior branches of the sacral spinal nerves exit through the dorsal sacral orifices. Distinguish the branches of cervical, thoracic, lumbar, sacral and coccygeal nerves.

The posterior branch of the first spinal nerve (CI) is called the suboccipital nerve (n. Suboccipitalis). It goes back between the occipital bone and the atlas, passes along the upper surface of the posterior arch of the atlant. This nerve is almost entirely motor, it innervates the upper and lower oblique muscles of the head, the posterior large and small rectus muscles of the head. A small number of sensitive fibers in its composition innervates the joints between the atlas and the axial vertebra, as well as the capsule of the atlanto-occipital joint. There is a constant connection of the suboccipital nerve with the posterior branch of the second cervical spinal nerve.

The posterior branch of the second cervical spinal nerve (CII) is a large occipital nerve (n. Occipitalis major) - thick, moving away from the second cervical spinal nerve at the lower edge of the lower oblique muscle (head). Next, the nerve passes between the lower oblique and semi-oval muscles of the head on the lateral surface of the ligamentous ligament. This nerve gives short muscle branches and a long cutaneous branch. Muscular branches innervate the semi-long and long muscles of the head, the waist muscles of the head and neck. A long branch of the nerve perforates the semimartial muscle of the head and trapezius muscle, accompanies the occipital artery. Together with this artery, the nerve rises to the top and innervates the skin of the occipital region. The posterior branches of the remaining cervical spinal nerves innervate the skin of the posterior region of the neck.

The posterior branches of the spinal nerves branch out in the muscles and back skin, which they innervate.

The posterior branches of the lumbar spinal nerves innervate the deep back muscles and the skin of the lumbar region. The three upper lateral branches run downward and lateral to the skin of the lateral half of the gluteal region and the large trochanter, forming the upper nerves of the buttocks (nn. Cluneum superiores).

The posterior branches of sacral and coccygeal spinal nerves consist mainly of sensitive fibers. The posterior branches of the four upper sacral spinal nerves pass through the dorsal sacral orifices, branch to the sacroiliac joint, innervate the skin of the posterior surface of the sacrum, and also form the middle nerves of the buttocks (nn. Cluneum medii). These nerves perforate the gluteus maximus and innervate the skin in the middle and lower gluteal regions. The posterior branches of the fifth sacrum and coccygeal spinal nerves pass next to the sacrococcygeal ligament (or perforate it), connect with the anal-coccygeal nerve (see "Coccygeal plexus") and innervate the skin in the region of the coccyx and anus.

The anterior branches of the spinal nerves (rr. Ventrales, s. Anteriores) innervate the muscles and skin of the anterior and lateral sections of the neck, chest, abdomen and extremities. The metameric structure retains only the branches of the thoracic spinal nerves. The anterior branches of the cervical, lumbar, sacral and coccygeal spinal nerves form plexuses. These plexuses are formed by connecting to each other adjacent spinal nerves. In the plexuses, there is an exchange of fibers belonging to neighboring segments of the spinal cord. Due to the redistribution of sensitive fibers in the plexus, the relationship of one part of the skin to the neighboring segments of the spinal cord is established, therefore, when external factors act on the skin, the reciprocal sigals are transferred to many muscles. As a result, the reliability of peripheral innervation rises and complex reflex responses of the organism are provided. Allocate cervical, brachial, lumbar, sacral and coccygeal plexus.

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