Nerve spinal

The spinaux nerves (in the past called rachidian nerves ) are the Nerf S which emergent of the Spinal-cord and not of the Cerveau. They are responsible for the Motricité and the sensitivity of the members, the Sphincter S and the Périnée.

Spinaux nerves at the man

The human being has 31 pairs of identified spinaux nerves each one by a letter and a number:

8 cervical (C1 with C8); (contrary to the others, the eighth cervical nerve emerges in lower part of the seventh cervical vertebra)
12 thoracic (T1 with T12);
5 lumbar (L1 with L5);
5 crowned (S1 with S5);
1 coccygien (C1) which is vestigial.

Roots of the spinaux nerves

Each nerve spinal is formed by the meeting of two rachidian roots, one dorsal sensitive and the other ventral motor coach. It is thus about a mixed nervous way (sensitive and driving). The two rachidian roots comprise also vegetative sympathetic nerves, respectively viscérosensitives nervous fibers and viscéromotrices.

The dorsal spinales roots present a bulge called Ganglion spinal in which the cellular bodies of the pseudo-unipolar sensitive neurons are. Each ganglion receives afférences of a cutaneous territory delimited on the surface of the body, these territories are organized in more or less parallel bands, called Dermatome S sensitive.

The ventral spinales roots are formed by the Axone S of the spinaux motoneurones which take part in particular in the medullary Arc reflex. The Fascicule of muscle fibreses innervés by these neurons constitute the Myotome what is called.

More generally, with each rachidian nerve a vertebral segment is associated or Neuromère which indicates the anatomical territory of influence of this nerve, i.e., the zone of the body innervée by this nerve starting from its vertebral emergence.

In the field of the cutaneous somesthesy, the rachidian segment is thus the sensitive dermatome.
In the driving field, it acts of the myotome.
the Viscérotome (or entérotome) indicates the Viscère S innervées by this nerve
the Sclérotome with the elements of the Squelette innervés by this nerve
the Angiotome corresponds to the Blood-vessels innervés by the nerve spinal
the Neurotome indicates nervous fabrics made up by the nerve spinal and the vegetative nervous fibers which are associated for him.

Emergence of the spinaux nerves

The nerve spinal emerges from the Spinal column, between each Vertèbre by the intervertebral Foramen (or Trou of conjugation). The first seven spinaux nerves (C1 with C7) emergent by the respective vertebral channel, i.e., C1 leaves to the top the first cervical vertebra, C2 with the top of the second, etc the nerve spinal C8 leaves him of below the seventh and last cervical vertebra (C7) and then, the nerves spinaux thoracic and lumbar emergent with the lower part of the corresponding vertebrae.

Each nerve spinal is divided then into two branches: a dorsal branch which innerve the Tegument S and muscles of the back, and a branch ventral, smaller, which innerve skin and muscles of the ventral face of the body and members. The two primary education branches themselves are subdivided in secondary branches: the dorsal branch in a side branch and a branch médiale, and the ventral branch in a former branch and a side branch.

Certain primary education ventral branches are anastomosed to form nervous Plexus:

the cervical Plexus (C1-C4) innerve the Neck, the perish-auricular area, the posterior part of the scalp, the upper part of the Thorax and the Diaphragme
the Plexus brachial (C5-T1) innerve the arm
the lumbar Plexus (on the level of L1-L3 and part of L4) innerve the abdomino-genital area
the Plexus crowned (L4-S3) innerve the Jambe
the T2 nerves in T12 do not form a plexus

The Fibers préganglionnaires sympathetic nerves separate from somatic and driving fibers of the primary education ventral branch to form the white communicating Rameau which joined the Ganglion paravertébral of the Chaîne sympathetic nerve. Of each emergent ganglion of the Fibers postganglionnaires which will join the nerve spinal via the Rameau communicating gray (which is not myelinized).

Until the third month of the fetal life , the spinal-cord occupies all the length of the rachidian Canal: each medullary segment is well opposite the foramen corresponding. But beyond 3 months, occurs a differential growth: the Rachis grows more quickly than the spinal-cord. At the adulthood, the spinal-cord is thus placed in the upper part of the rachidian channel. Consequently, the roots of the spinaux nerves posterior are not any more opposite their foramen, but well above. The roots must thus go down more and more vertically in the rachidian channel to join to them foramen. Under vertebrae L1/L2, beyond the final cone of the spinal-cord, in the Cul-de-sac dural, one thus finds only nervous fibers which form the final Filum what is called.

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