A dermatome is the area of ​​the skin that is autonomously innervated by the nerve fibers of a certain spinal cord root (spinal nerve root). The name "dermatome" comes from the Greek and is composed of the words for skin and section. Understanding the dermatomes is of great importance in medicine for various diseases.

Classification of the dermatomes

The basis for the formation of the dermatomes lies in the embryology. Owns an embryo three various Cotyledons (Ectoderm, Mesoderm and Endoderm), from which all different tissues develop in the course of its maturation.
In the trunk area, the so-called mesoderm initially form Primary vortex (Somites) on the side of the Neural tube are located. From the laterally-rear part of these primary vortices then ultimately form Subcutaneous tissue and skin. This creates a 1: 1 assignment of one Spinal nerves to a specific skin area.
The dermatomes are therefore also after the annoy named by which they are supplied.

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in the Cervical area is there 8 Spinal nerves associated with C1 to C8 The dermatomes are called accordingly. However, there is the only exception here: A C1 dermatome does not exist because the spinal nerve fiber of the first cervical vertebra has purely motor functions and does not innervate the skin. There are on the fuselage 12 Spinal nerves and thus 12 Dermatomes, Th1 to Th12. Lumbar and sacral vertebrae own each 5Hence, we have both the spinal nerves and the dermatomes L1 to L5 and S1 to S5.
This assignment, which was created so early, is also retained in adults. If you imagine that the person is bent over with both arms and legs roughly in the 90-degree angle Pointing from the back to the floor, the body can be roughly divided into strips, resulting in the dermatomes, starting with the dermatome C2 on the head and ending with the dermatome S5 on the back of the buttocks.

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It is important, however, that the dermatomes are not really separated from each other by clear lines, this picture is only for better understanding. In fact, the dermatomes partially overlap. It is assumed that this overlap is more pronounced for the sensation of touch stimuli than for the sensation of pain and temperature stimuli. Because of this phenomenon, those affected often do not notice if only one segment loses its function, since the innervation of the corresponding area is largely still guaranteed by the neighboring spinal nerve roots. The impairment usually only becomes apparent when two adjacent segments fail.
In contrast to the dermatomes, there are also the so-called autonomous areas on the skin. These are the supply areas of certain peripheral nerves, not the spinal nerve fibers. This makes a difference because the nerves that arise from the spinal cord split up and connect with nerve fibers from other nerves. This exchange of nerve fibers is also known as the plexus, and the result is the plexus nerves.

Transmission from internal organs

Also internal organs partially transmit sensations arising in them via the spinal nerves. Sometimes it works brain but not to assign the signals received in this way to an exact location, as is possible for the skin areas. The consequence of this is that the sensations originating from the organ affect the one belonging to the same spinal nerve Skin area be transmitted. So when there is a disease in an internal organ, pain may not be felt inside the body, but on the skin. This results in the allocation of various Head zones (first described by the English neurologist Head) on the skin.
Pathological processes in the heart typically lead to pain in the heart left-sided dermatome Th1 to Th5, a disease of liver or the Biliary tract leads to pain in the dermatomes Th6 to Rh9 right and so a place on the skin can be assigned to almost every organ. In some cases, the pain is not confined to one dermatome, but spreads to neighboring segments or spreads to the entire half of the body (Generalization). This phenomenon is known as transmitted pain. In the case of classic images, this transmitted pain can contribute to a diagnosis.

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disc prolapse

They are also important Dermatomes in the diagnosis of Herniated discs.
If the jelly-like core is a Intervertebral disc slips out and presses on a spinal nerve fiber (e.g. sciatic nerve), this leads to functional disorders of the segments that are supplied by this fiber. If sensitive failures are limited to a specific dermatome, this can be used to determine the location of a herniated disc.
The most common herniated discs occur in the L4 / 5 and L5 / S1 area.
Herniated discs in the area are typical L4 / L5what a restricted Sense of touch the Inside of the lower leg and des Foot leads, and in the field L5 / S1where there is, however, a Sensory disorder the Outside of the foot and the sole of the foot comes.

You can also read more on this topic at:

  • disc prolapse
    • Herniated disc L4 / 5
    • Herniated disc L5 / S1

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