Each of the spinal nerves exits the spinal canal between two of the vertebra. Each then goes to a particular area of the body. The area of skin served by each of these nerves is called its dermatome.
The nerves from the upper cervical spine serve the skin of the neck. The nerves from C5 to T1 (the mid-cervical spine to the upper thoracic spine) go to the arms. The nerves from T2 to L2 () go to the chest and abdomen. Those from L3 to S1 (lumbar and the first sacral) go to the skin of the legs. The remainder of the sacral nerves, and the coccygeal nerves, go to the groin.
For example, when the C6 nerve is pinched, there is pain and numbness in the thumb and index finger. When the L5 nerve is pinched, there is pain and numbness in the big or “great” toe.
List of Dermatomes of Commonly Injured Nerve Roots
C5 – The area over the shoulder.
C6 – The thumb and part of the forearm.
C7 – The middle finger.
C8 – The smallest fingers and part of the forearm.
L4 – The thigh.
L5 – The medial part of the calf and foot, the big toe.
S1 – The lateral part of the calf and foot, the smaller toes.