Dermatomes

Dermatomes, the segments of the skin into which the entire surface of the human body is divided in connection with the innervation of its various spinal cord roots. There are a number of schemes illustrating this division of the skin surface into segments or dermatomes; the schemes of Kocher and Seiffer are considered the most correct (see Figures 2–5). The lines dividing the dermatomes on the trunk are arranged transversely, while on the limbs they are longitudinal; the roots entering the brachial plexus innervate the upper limbs, those entering the lumbosacral plexus innervate the lower limbs; the roots of the thoracic segments innervate the trunk, the lower sacral roots innervate the perineum, the anus, and the genital organs. Each dermatome receives sensory fibers from a total of three roots—one main, basic root, which is reinforced by the lower and upper roots (see Figure 1); therefore, when one root is affected in the corresponding dermatome, disturbances of sensitivity may not be observed. This projection of spinal cord segments onto the skin is of very great importance in diagnosis, as it allows the exact localization of the location of the pathological process in the spinal cord.

Figure 1. Distribution of sensory fibers in the skin. Scheme of overlaying the upper and lower roots on the main one.

Figure 2 and 3. Scheme of distribution of fibers of the posterior spinal roots in the skin on the anterior and posterior surfaces of the body according to Kocher.

Figure 4 and 5. The same according to Seiffer.