Dermatomes are certain areas of the body innervated by a nerve that exits the spine. The spine is composed of 33 vertebrae and has 31 pairs of nerves that are distributed throughout the body, in an organized way.
Each nerve that leaves the spine is responsible for imparting sensitivity and strength to a certain area of the body, and so whenever a nerve is compressed or cut, a certain area of the body is compromised. In this way it is possible to identify which part of the spinal cord was affected by compression, trauma or herniated disc, when a person says that he feels tingling, weakness or inability to move an arm or the side of the foot, for example.
Altogether there are 31 dermatomes that are divided as if in 'slices', as shown in the following image:
Map of body dermatomes
The best way to identify all dermatomes in the body is to observe a person in the position of 4 supports, because that way the 'slices' are easier to be perceived. The following are the main dermatomes of the body:
- Cervical dermatomes - Face and neck: they are specially innervated by the nerve that exits the C1 and C2 vertebrae; Thoracic dermatomes - Thorax: these are the regions enervated by nerves that leave vertebrae T2 to T12; Dermatomes of the upper limbs - Arms and hands: they are innervated by the nerves that leave the vertebrae C5 to T2; Lumbar and lower extremity dermatomes - Legs and feet: contain the regions innervated by the nerves that leave the vertebrae L1 to S1; Buttocks: is the area innervated by the nerves that are in the sacrum, in S2 to S5.
The map of dermatomes are generally used by doctors and physiotherapists to identify the presence of changes or compressions in the spinal cord, since, in case of changes in sensitivity in a certain area of the body, it is easier to identify where the spine is being compromised, for example. a trauma or herniated disc, for example.
But in addition, dermatomes can also be used in alternative therapies, such as acupuncture or reflexology, to directly stimulate certain locations in the spinal cord or other organs innervated by the corresponding nerve pair. This way the acupuncturist can insert a needle in the spine, in order to relieve the pain and discomfort that arise in other areas of the body.
Difference between dermatome and myotome
Dermatomes refer to sensory changes in the skin, while myotomes are responsible for the movement of muscles in the same region. The table below shows some examples:
| Nervous root - Myotome | Movements | Nervous root - Myotome | Movements |
| C1 | Flex the head | T2 to T12 | - |
| C2 | Extend your head | L2 | Flex the thigh |
| C3 | Flex the head laterally | L3 | Extend the knee |
| C4 | Raise your shoulder | L4 | Dorsiflexion |
| C5 | Abduct the arm | L5 | Hallux extension |
| C6 | Flex the forearm and wrist extension | S1 | Foot eversion + thigh extension + knee flexion |
| C7 | Extend the forearm and flex the wrist | S2 | Knee flexion |
| C8 | Extend thumb and ulnar deviation of that finger | S3 | Intrinsic muscles of the foot |
| T1 | Open and close fingers | S4 and S5 | Perennial movements |
Thus, when the person has a sensation of numbness on the side of the foot, the most likely is that there will be an alteration in the spine, more specifically between the L5 and S1 vertebrae, because this is their dermatome. But when it has weakness and difficulty in bending the arm, the affected region is the cervical, specifically C6 and C7, because this region is its myotome.
