Spinal Cord Nerves

Synonyms

Medical: Nervi spinal spinal nerves, CNS, spinal cord, brain, nerve cell

Declaration

Humans possess 31 pairs of spinal nerves (spinal cord nerves), which pass between the individual vertebrae through the intervertebral holes, i.e. (almost) analogous to the division of the spinal cord on each side: this uniform structure can give the impression of segmentation, which is why it is often referred to as “spinal cord segments”.

8neck nerves, (Nervi cervicales)
12 thoracic nerves (Nervi thoracales)
5Lumbar nerves (Nervi lumbales)
5 sacral nerves (Nervi sacrales) and
1coccyx ganglion nerve.

The Spinal Nerves

This term “spinal cord segments” has a purely practical meaning, it serves, among other things, to describe a specific level of the spinal cord; for example, the navel is located “at the level of Th 10”, which means at the level between the 10th and 11th thoracic vertebrae (Th for thoracic segment). In general, the human body has variable 31 to 33 spinal nerves. Although he has only seven cervical vertebrae, eight pairs of spinal nerve roots, also known as cervical roots (cervix = neck), branch off from the cervical marrow: This is explained by the fact that the spinal root, abbreviated C 1, which belongs to the first cervical segment, leaves the spinal cord between the bony skull and the first cervical vertebra (atlas).

In the area of the cervical spine, the spinal roots are therefore named after the vertebra below them. The root belonging to the eighth segment of the cervical spine leaves the spinal cord between the seventh cervical vertebra and the first thoracic vertebra. Therefore, from here on, all other spinal roots leaving the spinal cord are named after the vertebra above them (the root L 4, for example, leaves the spinal cord between the fourth and fifth lumbar vertebrae), and the number of segments of the spinal cord corresponds to the number of vertebrae.

From the thoracic spine onwards, the number of spinal nerves corresponds to the number of vertebral bodies; accordingly, twelve spinal nerves in the thoracic spine, five in the lumbar spine, and further caudally (below) in the sacrum, another five spinal nerves. In the lowest part of the spinal column, at the coccyx, another one to three spinal nerves emerge variably. The knowledge of this is important for the physician in order to better locate disease processes in the spinal cord on the basis of clinical symptoms: For example, an intervertebral disc that presses on the root L4 makes a very specific pattern of failures (clinical symptoms), a so-called root syndrome.

If the doctor sees this pattern, he can deduce that it must be the intervertebral disc between the fourth and fifth lumbar vertebrae. A segment thus corresponds to a specific spinal segment that supplies the fibers for a specific spinal nerve (a specific spinal root), even if this spinal nerve later splits up again into individual nerves – although these parts do not necessarily have to be close together.

The 1st chest segment the 7th cervical vertebral body,
The 1st lumbar segment the 10th thoracic vertebral body,
The 1st sacrum segment opposite the 1st lumbar vertebral body.

Spinal cord nerves are also known as spinal nerves in technical terminology.

They do not belong to the central nervous system but to the peripheral nervous system and are formed by the union of the front root and the rear root of the spinal cord. The spinal nerves serve to transmit information from the spinal cord [coming from the central nervous system (CNS)] to organs, muscles and all other parts of the body or they transport information from these areas of the body to the spinal cord, from where it is transmitted further into the CNS. They can therefore be roughly divided into two groups: The nerves that carry information from the spinal cord to further peripherally are called efferent; they originate from the anterior horn of the spinal cord and, for example, transmit the “order” of movement of a muscle, which originated in the central nervous system, to this muscle.

Information on the regulation of organ functions such as an increase or decrease in intestinal activity or an increased or decreased secretion of digestive juices is also passed on via efferent nerves. The second type of fiber, which is carried by a spinal nerve, transmits information in the opposite direction, i.e. from the periphery towards the spinal cord, entering the posterior horn; it is called afferent.They serve, for example, to transmit sensitive perceptions such as touch, temperature, pain and sense of position to the central nervous system. Sensitive perceptions of organs, for example the filling of the stomach, are also transmitted to the central nervous system.

The nerve emerges through the intervertebral hole and divides into different branches: The spinal nerve itself, which is only about one centimeter long before it divides into several nerves, contains both the afferent and the efferent nerve components and carries the four qualities described above, which are summarized here once again in brief: somato-efferent (information that leads, for example, to muscle movement), somato-afferent (information about sensitive perceptions about the skin), viszero-efferent (information that influences organ activity) and viszero-afferent (information about the condition of the organs). The spinal nerve thus also contains nerve components that serve the regulation of the autonomous (vegetative) nervous system – the sympathetic and parasympathetic nerves. Information is transported here that regulates, among other things, vegetative bodily functions such as sweat secretion, heart rate, intestinal activity or pupil width.

In principle, each pair of spinal nerves sensitively supplies a specific body segment. Thus, the innervation of the skin is striped, especially on the trunk, these stripes are called dermatomes. The pair of spinal nerves, which emerges under the fifth thoracic vertebra (Th 5), supplies a strip of skin that runs along the nipples.

The pair of spinal nerves that emerge below the tenth thoracic vertebra (Th 12) is responsible for the sensitive innervation of a strip of skin that includes the navel. However, the innervation of the dermatomes is always overlapping, i.e. the dermatome Th 10 is also innervated by the spinal nerve segment Th 9 in the upper area and by the segment Th 11 in the lower area. This has the great advantage that in case of failure of the spinal nerve segment Th 10, there is no complete numbness in the affected dermatome.

It is more difficult in the area of the arms and legs: The segmental division has developed much earlier in the developmental history of vertebrates than in humans and strictly speaking refers to the “quadruped”. This is why a pair of spinal nerves that leave the spinal cord on each side of the body between the sixth and seventh cervical vertebrae, i.e. belong to cervical segment 6 (abbreviated C 6), supplies (innervates) for example the skin of the thumb and not the skin that lies over the sixth cervical vertebra. The supply to the muscles is even more complex than that to the skin: a muscle area supplied by a spinal nerve (myotome) does not necessarily have to lie directly under the skin area supplied (dermatome), but can be located somewhere else.

In addition, a muscle is always supplied by the spinal nerves of several segments. If, for example, the spinal cord or an exiting spinal nerve root is damaged at a certain height, not the entire muscle will fail (be paralyzed) – the co-provisioning ensures that it is only weakened (= paretic). Also the reflexes are usually only weakened, not completely extinguished.

Some of the spinal nerves form so-called plexuses, i.e. nerve plexuses. Here, several spinal nerves mix together and move further to the periphery. Therefore, this strictly stripe-shaped and segmental innervation for sensitive perceptions does not apply to all areas of the body; especially on arms and legs, such plexus formation takes place.

The innervation of the muscles is also usually not supported by a spinal nerve segment alone. The individual segments have their so-called identification muscles (for example, the biceps muscle – Musculus biceps brachii – is primarily supplied by spinal nerve segments C 5 and C 6 (fifth and sixth spinal nerve in the cervical spine). This characteristic is used in the diagnosis and height localization of a herniated disc (prolapse), since weakening (paresis) of the corresponding muscle gives a strong indication of the affected segment.

The most important plexuses are the brachial plexus, the brachial plexus, and the lumbosacral plexus for the lumbar and leg region.

Into a front branch to supply the skin and muscles of the front of the body (ramus anteriorventralis),
Into a posterior branch to supply skin and muscles of the back of the body (ramus posteriordorsalis),
Into a “connecting” branch (Ramus communicans), which guides vegetative information and
Into a small sensitive branch to supply the pain-sensitive spinal meninges (ramus meningeus).

The most common form of impairment of spinal nerves is involvement in the sense of a root syndrome, which means that in the context of various diseases one (or more) nerve roots are affected in whatever way and then failures occur according to their own conduction qualities. In relation to a certain body part (corresponding to a segment), these are above all: there are many causes for irritation of a spinal nerve root (spinal cord nerve root), especially in connection with degenerative changes in the spinal column, such as a herniated disc or spinal canal stenosis, where a root is ultimately compressed and thus irritated.

The continuous irritation of a nerve root in the spinal column can lead to nerve root inflammation, which manifests itself in the above-mentioned symptoms. This is usually the case in the lower segments (lumbar region) or also in the cervical segments. Diseases that affect a spinal root or spinal nerve (spinal cord nerve) DIRECTLY, i.e.

not in the sense of a compression syndrome, tend to be of an inflammatory nature and are usually caused by “neurotropic” (i.e. “nerve-loving”) pathogens. In addition, the peripheral nervous system is usually also involved in the sense of a radiculopathy neuropathy (i.e. pathological events without inflammation) in cases of poisoning (e.g.

lead) or metabolic disorders (e.g. diabetes mellitus), but these usually do not cause any clear symptoms. And finally, there are nerve irritation syndromes of which nobody knows the cause (idiopathic). A spinal nerve root (spinal cord root) can be irritated by 1. space-occupying processes such as a 2. inflammatory cause (radiculitis), a distinction is made here

Pain
Miss sensations like tingling (= paresthesia)
Emotional disorders up to deafness
Muscle weakness (paralysis) and reflex weakening
Herniated disc: The leaked disc presses on the root
Abscess: the colonization and local reproduction of bacteria, which continue to grow in a “pus cavity”, presses on the root
Hematoma: Bleedings also demand space
Tumor occurrence: Tumors of the spinal cord itself or metastases of other tumors in the spine can press on the nerves
Inflammation caused by the pathogen, e.g. in the context of neuroborreliosis (borreliosis) caused by the bacterium Borrelia burgdorferi or shingles (zoster), in which the varicella zoster virus attacks the sensitive ganglion cells and spreads along the associated spinal (or facial) nerve and causes pain
Z.
B. in the context of neuroborreliosis (borreliosis) caused by the bacterium Borrelia burgdorferi or
Shingles (zoster), in which the varicella zoster virus infects the sensitive ganglion cells and spreads along the associated spinal (or facial) nerve, causing pain
Autoimmunologically caused inflammation e.g. Guillain-Barré syndrome with symmetrical paralysis rising from the legs (up to respiratory paralysis) with destruction of the insulating myelin sheaths by the formation of antibodies directed against nerve components (autoantibodies).
Z. B. Guillain-Barré syndrome with symmetrical paralysis rising from the legs (up to respiratory paralysis) with destruction of the isolating myelin sheaths by the formation of antibodies directed against nerve components (autoantibodies).
Z. B. in the context of neuroborreliosis (borreliosis) caused by the bacterium Borrelia burgdorferi or
Shingles (zoster), in which the varicella zoster virus infects the sensitive ganglion cells and spreads along the associated spinal (or facial) nerve, causing pain
Z. B. Guillain-Barré syndrome with symmetrical paralysis rising from the legs (up to respiratory paralysis) with destruction of the isolating myelin sheaths by the formation of antibodies directed against nerve components (autoantibodies).