Dermatome Map – Overview Chart, Anatomy, & Clinical Significance
Did you ever wonder why pain in your back send tingling sensations down your legs or a crick in your neck made your fingers feel numb?
The relationship between sensations and irregularities on or near the surface of the skin in certain areas of your body is connected to specific nerve roots that are located along your spine. Those areas that are affected by each specific nerve root are what referred to as dermatomes.
Understanding the dermatome chart of the human body can help you and your health care provider in diagnosing the root of a particular illness or injury.
Let’s take a closer look at the dematome map and how it is used in diagnoses and treatment.
What is a dermatome?
The combination of two words: dermat, which means skin and ome, which means mass.
It is a mass of nerves on the skins surface that are related to each other, having derived from the same somite groups during embryonic development.
Each dermatome is a region of the skin’s surface in which the sensory nerves draw from a specific spinal nerve root. For example, the nerve fibers on surface of the skin that run along the outer portion of the thigh and then along the front of the lower leg, shin, foot and toes are a dermatome that are derived from a nerve root in the lower back.
Dermatome along the thoracic and abdominal regions of the body are stacked like discs. Along the arms and legs, however, they run in a longitudinal pattern along the length of the limbs.
The general pattern of dermatome is similar in all humans, but the precise area where the nerve fibers are placed is as unique as the fingerprints of an individual.
What is the difference between myotomes and dermatome?
To understand the difference between myotomes and dermatome, you have to understand that cells from each embryonic somite differentiate into three different types during development.
Those three types are:
- Myotome cells develop into skeletal muscle.
- Dermatome cells develop into connective tissue and skin.
- Sclerotome cells develop into vertebrae.
The difference between myotomes and dermatome is that myotomes are related to the muscles within the somite group and dermatome are related to the skin and surface tissues of the somite group.
Why are dermatome clinically important?
Dermatome are clinically important because they aid the process of diagnosing the cause of symptoms that a patent presents.
Since a particular area of the skin is supplied by sensory neurons that come out of a specific spinal nerve ganglion, symptoms that are located along or within the area of a dermatome (e.g. like pain, skin irritation, or a rash) may point to a cause that is associated with the related nerve root.
For example, a herniated disk that is pinching the L5 nerve root causes pain and tingling in the lower leg and foot.
Some skin problems relate to injuries along the nerve path between the area where they are felt and the related spinal root of the dermatome where they are located.
Viral conditions like chickenpox and shingles typically lie dormant within specific nerve ganglia until they develop as pain, a rash or both. Those conditions develop in a pattern that is consistent with their associated dermatome, but their resulting symptoms don’t always cover the entire dermatome.
What is a dermatome map or chart?
A dematome map or dermatome chart is a schematic representation of the area each dermatome covers and the location of its specific nerve root.
They are typically color coded in their own groupings, which match up with the somite from which they developed.
Dermatome maps are used to specifically locate where a particular pain or skin irritation is originating. They are most commonly used in pinpointing the exact location of the injury related to back and neck pain that create referred pain in other areas of the body; like the example above where numbness, pain and tingling in the toes was related to a nerve injury at the L5 nerve root.
To locate the dermatome level of a particular abnormality, health care providers can use a pin or a cold tuning fork to move from the area of abnormality along the chest or back on either side until they reach a point of normality. Once the point of normality is reached, the area of injury can be determined.
How many dermatome are there?
There are 29 dermatomes related to the 30 nerve roots along the spine.
There are 8 cervical nerve roots of which 7 of them have a connected dermatomes. The thoracic region has 12 dermatome related to the 12 thoracic nerve roots. The lumbar and sacral regions of the spine each have 5 lumbar nerves roots with 5 connected dermatome.
The dermatome and their corresponding nerve roots are labeled in relation to the vertebrae where the nerve root departs from the spinal cord and pass through the small openings between the vertebrae.
Thus the dermatome corresponding to the nerve root departing from the spinal cord at the vertebrae labeled L5 is also labeled as L5.
The dermatome associated with the nerve roots located in the neck and shoulders portion of the spine are labeled from C1 through C8.
Viewed from the front with the palms facing forward, these are the areas that each of the 7 cervical dermatome cover:
The dermatome associated with the nerve roots located in the upper and middle portion of the spine are labeled from T1 through T12.
The dermatome along the back in the thoracic region are narrow strips stacked in equal portions like discs. Viewed from the front with the palms facing forward, these are the areas that each of the 12 cervical dermatome cover:
The dermatome associated with the nerve roots located in the lower portion of the spine, but above the buttocks are labeled from L1 through L5.
L1 through L3 across the back are similar to the thoracic vertebrae and are stacked in narrow discs, but below that point, they broaden and include other parts of the buttocks. Viewed from the front, these are the areas that each of the 5 lumbar dermatome cover:
The dermatome associated with the nerve roots located in the sacral area of the lower and into the tailbone are labeled from S1 through S5.
Viewed from the front, only the S1 dermatome is included. Viewed from the back, these are the areas that each of the 5 sacral dermatome cover:
The dermatome map is a useful tool that is made use of in pinpointing the affected area of nerve damage in injuries and illnesses.
Having an understanding of the dermatome map and how it affects your health can help you better communicate the source of your pain or abnormality to your health care provider.