Transmission from internal organs
Internal organs also transmit sensations that arise in them partly via the spinal nerves. Sometimes, however, the brain does not succeed in assigning the signals received in this way to an exact location, as is possible for skin areas. As a result, the sensations originating from the organ are transmitted to the skin area belonging to the same spinal nerve.
So if there is a disease in an internal organ, it is possible that pain is not felt inside the body but on the skin. This results in the allocation of different Head zones (first described by the English neurologist Head) on the skin. Pathological processes in the heart typically lead to pain in the left-sided dermatome Th1 to Th5, a disease of the liver or the bile ducts leads to pain in the dermatomes Th6 to Th9 on the right side and thus almost every organ can be assigned a location on the skin.
In some cases the pain is not limited to one dermatome but spreads to the adjacent segments or affects the entire half of the body (generalisation). This phenomenon is called transmitted pain. In classical images, this transmitted pain can help to establish a diagnosis.
Slipped disc
In addition, the dermatomes are important in the diagnosis of herniated discs. If the jelly-like core of an intervertebral disc slips out and presses on a spinal nerve fibre (e.g. sciatic nerve), functional disorders of the segments supplied by this fibre occur. So if sensitive failures are limited to a certain dermatome, the location of a herniated disc can be inferred.
The most frequent herniated discs occur in the area of L4/5 and L5/S1. Typical are herniated disks in the area L4/L5, which leads to a limited sensation of touch of the inner side of the lower leg and the foot, and in the area L5/S1, where, on the other hand, a sensory disturbance of the outer side of the foot and the sole of the foot occurs.
