Full Dermatome Zones (Posterior) Description
[Continued from above] . . . as opposed to the posterior aspect. The apparently uneven dermatome arrangement in the arm and leg areas can probably be attributed to the uneven rate of nerve growth into the limb buds. Actually, the dermatomes overlap only slightly.
Every nerve sends information about different sensations on a certain area of the skin. The spinal nerves include eight cervical nerves (although C1 has no dermatome), which represent dermatomes from the head through the upper back and posterior areas of the arms; twelve thoracic nerves, which include the middle back and portions of the arms; five lumbar nerves which have dermatomes in the lower back and legs and feet; and five sacral nerves with dermatomes in the posterior of the body along the buttocks and backs of the legs and feet.
The pattern of the dermatome is of major clinical significance when a physician wants to anesthetize a particular portion of the body. As certain areas of the body are much more sensitive than others, it is sometimes necessary to block more than one dermatome to produce a desired result. Because adjacent dermatomes overlap in the arms, legs, groin and buttocks areas, at least three spinal nerves must be blocked to achieve a loss of feeling in these regions. Abnormally functioning dermatomes provide important clues about injury to the spinal cord or specific spinal nerves. For example, if a dermatome is stimulated but no sensation is perceived, it can be inferred that the nerve to that specific dermatome has been injured.