Dermatomes

The body has 31 pairs of spinal nerves, which are nerves extending from the spine to all parts of the body. A dermatome is a specific area of skin supplied by a single spinal nerve.

There are 8 pairs of spinal nerves in the neck, supplying 16 dermatomes. The thoracic spine has 12 pairs of spinal nerves, supplying 24 dermatomes. The lower back and sacrum each have 5 pairs of spinal nerves, supplying 10 dermatomes, while the coccyx has only 1 pair of nerves, supplying 2 dermatomes.

Below is an overview of the dermatomes on the front and back of the body.

Dermatomes front (ventral)

Dermatomes back (dorsal)

Description of the dermatomes per level

C2 – Temple and occiput. C3 – Area at the height of a jumper's collar. C4 – Lower neck. C5 – Outside of the shoulder (deltoid area). C6 – Thumb and index finger. C7 – Middle part of the hand and fingers. C8 – Ring finger and little finger. T1 – Part of the lower and upper arm up to the start of the hand. T2 – Part of the upper arm. T3 – Armpit. T4 – Nipples. T5 – Inframammary fold. T6 / T7 – Xiphoid process of the sternum (processus xiphoideus). T10 – Navel (often first symptom of appendicitis). T12 – Pubic region. L1 – Back, top of ilium and groin. L2 – Back, ilium, front of thigh and scrotum. L3 – Back of hip, area above kneecap and inner side of knee/lower leg. L4 – Area around kneecap, outer buttock region, outer thigh, front of lower leg, inner side of foot, start of big toe. L5 – 1st (big) and 2nd toe. S1 – 3rd, 4th and 5th toe, heel. S2 – Buttock region, inner thigh and lower leg, genitals. S3 – Buttock region, back of thigh, genitals. S4 – Area around the anus. S5 – Anus.

Arrangement of dermatomes

As seen in the images, the dermatomes of the trunk are stacked logically. In the arms and legs, the dermatomes run longitudinally, which may seem illogical at first glance. However, if you imagine the body on hands and feet like a quadruped, the dermatomes align neatly in one line. This reflects our evolutionary descent from apes, who naturally walked on all fours before humans adopted an upright posture.

Medical significance

A dermatome is supplied by sensory nerves, which belong to a specific nerve root ganglion located just in front of the spine. Symptoms in a particular dermatome can indicate issues with the corresponding ganglion. For example, a herniated disc can compress a nerve, causing symptoms like tingling and numbness in the dermatome it supplies.

Each spinal nerve supplies one specific skin area on one side of the body and also controls certain muscles. When a nerve is compressed, weakness can occur in the muscles it controls. These muscle groups, controlled by a single nerve, are called myotomes.