The surface of the skin is divided into specific areas, called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root. (Sensory nerves carry sensory information—about such things as touch, pain, temperature, vibration, and position of a body part—to the spinal cord.)
There are dermatomes for each of these nerve roots.
Sensory information from a specific dermatome is carried by sensory nerve fibers to the spinal nerve root of a specific vertebra. For example, sensory information from a strip of skin along the back of the thigh, is carried by sensory nerve fibers to the 2nd sacral vertebra (S2) nerve root.