Introduction to spinal nerves

In this note, we are going to discuss the anatomy and function of the spinal nerves (nervi spinales).

Before diving into it, let’s recall that the nervous system is structurally subdivided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS).

Spinal nerves (nervi spinales) arise from the spinal cord. There are 8 cervical (C),

Cervical part of the spinal cord (pars cervicalis)

12 thoracic (Th),

Thoracic part of the spinal cord (pars thoracica)

5 lumbar (L),

5 sacral (S),

Sacral part of the spinal cord (pars sacralis)

and 1 coccygeal (Co) spinal nerves.

Coccygeal part of the spinal cord (pars coccygea)

Spinal nerves are formed by two roots: the anterior root (radix anterior) and the posterior root (radix dorsalis),

which merge in the intervertebral foramen.

The sensory spinal ganglion (ganglion spinale), which contains cell bodies of peripheral sensory neurons, adheres to the posterior root. In humans, these neurons are pseudounipolar.

Sensory spinal ganglion (ganglion sensorium nervi spinalis / ganglion spinale)

The peripheral process ends with receptors, and the central process enters the posterior horn of the spinal cord as part of the posterior root of the spinal nerve.

The anterior root consists of motor or efferent fibers coming out of the anterior horn of the spinal cord.

Efferent fibers heading to the target organs

These fibers carry motor information from the CNS to the target organs, for example, to muscles of the body.

The autonomic (sympathetic) fibers enter into the spinal nerves at the level between the first thoracic to the second lumbar segments (Th1-L2). The cell bodies of these sympathetic neurons are located in the lateral horns of the spinal cord (which can be found in all thoracic and the 1st and 2nd lumbar segments of the spinal cord, and some sources also include the 8th cervical segment.

Lateral horn (cornu laterale) contains cell bodies of sympathetic neurons

For the most part, the spinal nerves exit the spinal canal through the intervertebral foramen (foramen intervertebrale) under the corresponding vertebra.

Only 7 superior cervical nerves do it the other way around, passing through the intervertebral foramen above the corresponding vertebra.

Spinal nerve roots projections on the vertebral column

In the sacral region, the nerves exit through the sacral foramina (foramina sacralia).

Anterior sacral foramina (foramina sacralia anteriora)

Posterior sacral foramina (foramina sacralia posteriora)

Then each spinal nerve is divided into three branches: the anterior, posterior and meningeal branches.

The meningeal branch (ramus meningeus) goes back into the spinal canal through the intervertebral foramen and innervates the spinal meninges.

The posterior or dorsal ramus (r. posterior) passes posteriorly between the transverse processes of the vertebrae and innervates the post-vertebral muscles and the skin of the back.

The anterior or ventral ramus (r. anterior) innervates the skin and muscles of the neck, anterior aspect of the trunk and limbs.

The thoracic anterior rami remain segmental and become the intercostal nerves (nn. intercostales) in the intercostal spaces.

In the other parts of the body, the anterior rami interconnect with each other, forming the cervical plexus,

brachial plexus,

lumbar plexus,

sacral plexus,

and coccygeal plexuse, which give rise to the peripheral nerves.

Moreover, there are two types of branches that connect the spinal nerves and the sympathetic trunk.

White rami communicantes (rr. communicantes albi) only exit the spinal cord between the levels of T1-L2. They carry preganglionic sympathetic fibers that pass to the ganglia of the sympathetic trunk.

White rami communicantes (r. communicans albus)

Gray rami communicantes (rr. communicantes grisei) exist at all levels of the spinal cord. They carry postganglionic sympathetic fibers from the ganglia of the sympathetic trunk to the target organs.

Gray rami communicantes (r. communicans griseus)

In the following videos, we will focus in greater detail on specific nerve plexuses and their nerves.

более подробно остановимся на конкретных нервных сплетениях и входящих в них нервах.

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