Spinal nerves are metamerposed, paired nerve trunks. The number of spinal nerves, or rather, their pairs, corresponds to the number of pairs of segments of the spinal cord and is thirty-one: eight pairs of cervical nerves, twelve pairs of the pectoral, five lumbar, five cruciate and one pair of coccygeal nerves. With their help, the back of the brain analyzes the condition and exercises control of the trunk, pelvis, limbs, internal organs of the abdominal and chest cavity.
By their origin, the spinal nerves correspond to a certain part of the body, that is, the area of the skin developed from a certain somite is derived from dermatosis, from the myotome - muscles, from the sclerotome - bones. Each nerve originates from the "personal" intervertebral foramen, while it is formed from the anterior (motor) and posterior (sensitive) roots connected in the same trunk.
The spinal nerves reach a length of just one and a half centimeters, at the end they all branch out in the same way into the posterior and anterior membranous branches.
The back branch extends between the vertebrae and the transverse processes of the pair to the back, where it contributes to the innervation of the deep muscles (unbend the trunk) and skin. The spinal nerves of the posterior branches return back between the transverse vertebrae, in particular between their processes, and around their articular processes. Excluding the first cervical, as well as the fourth, fifth coccygeal and sacral, the vertebrae are divided into ramus medialis and lateralis, which supply the posterior surface of the skin of the neck and back, neck, and deep spinal muscles.
In addition, two more branches depart from the spinal nerves: the connecting branch - to the sympathetic trunk (for innervating the vessels and viscera), and the returning branch - going to the intervertebral foramen (for innervating the membranes of the spinal cord).
The plexuses of the spinal nerves of the anterior branches are more complex and innervate the skin and muscles of the ventral wall of the trunk and both pairs of limbs. Since in its lower part the skin of the abdomen takes an active part in the formation of the external genitalia, the skin that covers them is also innervated by the anterior branches. With the exception of the first two, the latter branches are much larger than the posterior ones.
The plexuses of the spinal nerves of the anterior branches in their original metomeric structure are preserved only in the thoracic region. In other departments that are associated with the limbs (during the development of which segmentation is lost), fibers extending from the spinal anterior branches are intertwined. Thus, the formation of the nerve plexus (plexus) takes place , where the interchange of various neuromer fibers occurs. In these plexuses, a large number of spinal nerves takes part in a very complex process in which the redistribution of fibers takes place: the peripheral nerves receive from the front branches of each spinal nerve fiber, which means the fact that each peripheral nerve contains fibers from many segments of the spinal cord.
Plexuses differ in three types: lumbosacral, brachial and cervical. The lumbosacral, in turn, is divided into coccygeal, sacral and lumbar.
From the above it should be concluded that the defeat and damage of a certain nerve does not entail a functional impairment of all muscles that receive innervation from the segments giving rise to this nerve. The spinal nerves extending from the plexuses are mixed, as a result of which the picture of nerve damage is composed of sensory impairment, autonomic disorders, as well as motor disorders.