A dermatome is an area of skin supplied by a single spinal nerve. There are 31 pairs of spinal nerves, forming nerve roots that branch from your spinal cord.
Your spinal nerves help to relay sensory, motor, and autonomic information between the rest of your body and your central nervous system (CNS).
So why are dermatomes important? How many are there? And where can they be found? Continue reading as we answer these questions and more.
Each of your dermatomes is supplied by a single spinal nerve. Let’s take a closer look at both of these components of the body.
Your spinal nerves
Spinal nerves are part of your peripheral nervous system (PNS). Your PNS works to connect the rest of your body with your CNS, which is made up of your brain and spinal cord.
You have 31 pairs of spinal nerves. They form nerve roots that branch from your spinal cord. Spinal nerves are named and grouped by the region of the spine that they’re associated with.
The five groups of spinal nerves are:
- Cervical nerves. There are eight pairs of these cervical nerves, numbered C1 through C8. They originate from your neck.
- Thoracic nerves. You have 12 pairs of thoracic nerves that are numbered T1 through T12. They originate in the part of your spine that makes up your torso.
- Lumbar nerves. There are five pairs of lumbar spinal nerves, designated L1 through L5. They come from the part of your spine that makes up your lower back.
- Sacral nerves. Like the lumbar spinal nerves, you also have five pairs of sacral spinal nerves. They’re associated with your sacrum, which is one of the bones found in your pelvis.
- Coccygeal nerves. You only have a single pair of coccygeal spinal nerves. This pair of nerves originates from the area of your coccyx, or tailbone.
Each of your dermatomes is associated with a single spinal nerve. These nerves transmit sensations, such as pain, from a specific area of your skin to your CNS.
Your body has 30 dermatomes. You may have noticed that this is one less than the number of spinal nerves. This is because the C1 spinal nerve typically doesn’t have a sensory root. As a result, dermatomes begin with spinal nerve C2.
Dermatomes have a segmented distribution throughout your body. The exact dermatome pattern can actually vary from person to person. Some overlap between neighboring dermatomes may also occur.
Because your spinal nerves exit your spine laterally, dermatomes associated with your torso and core are distributed horizontally. When viewed on a body map, they appear very much like stacked discs.
The dermatome pattern in the limbs is slightly different. This is due to the shape of the limbs as compared with the rest of the body. In general, dermatomes associated with your limbs run vertically along the long axis of the limbs, such as down your leg.
Your dermatomes are numbered based on which spinal nerve they correspond to. Below, we’ll outline each dermatome and the area of the body that it’s associated with.
Remember that the exact area that a dermatome may cover can vary by individual. Some overlap is also possible. As such, consider the outline below to be a general guide.
Cervical spinal nerves
- C2: lower jaw, back of the head
- C3: upper neck, back of the head
- C4: lower neck, upper shoulders
- C5: area of the collarbones, upper shoulders
- C6: shoulders, outside of arm, thumb
- C7: upper back, back of arm, pointer and middle finger
- C8: upper back, inside of arm, ring and little finger
Thoracic spinal nerves
- T1: upper chest and back, armpit, front of arm
- T2: upper chest and back
- T3: upper chest and back
- T4: upper chest (area of nipples) and back
- T5: mid-chest and back
- T6: mid-chest and back
- T7: mid-chest and back
- T8: upper abdomen and mid-back
- T9: upper abdomen and mid-back
- T10: abdomen (area of belly button) and mid-back
- T11: abdomen and mid-back
- T12: lower abdomen and mid-back
Lumbar spinal nerves
- L1: lower back, hips, groin
- L2: lower back, front and inside of thigh
- L3: lower back, front and inside of thigh
- L4: lower back, front of thigh and calf, area of knee, inside of ankle
- L5: lower back, front and outside of calf, top and bottom of foot, first four toes
Sacral spinal nerves
- S1: lower back, back of thigh, back and inside of calf, last toe
- S2: buttocks, genitals, back of thigh and calf
- S3: buttocks, genitals
- S4: buttocks
- S5: buttocks
Coccygeal spinal nerves
buttocks, area of tailbone
Dermatomes are important because they can help to assess and diagnose a variety of conditions. For instance, symptoms that occur along a specific dermatome may indicate a problem with a specific nerve root in the spine.
Examples of this include:
- Radiculopathies. This refers to conditions in which a nerve root in the spine is compressed or pinched. Symptoms can include pain, weakness, and tingling sensations. Pain from radiculopathies can follow one or more dermatomes. One form of a radiculopathy is sciatica.
- Shingles. Shingles is a reactivation of the varicella zoster (chickenpox) virus that lies dormant in the nerve roots of your body. Symptoms of shingles, such as pain and a rash, occur along dermatomes associated with the affected nerve root.
Dermatomes are areas of skin that are connected to a single spinal nerve. You have 31 spinal nerves and 30 dermatomes. The exact area that each dermatome covers can be different from person to person.
Spinal nerves help to relay information from other parts of your body to your central nervous system. As such, each dermatome transmits sensory details from a particular area of skin back to your brain.
Dermatomes can be helpful in evaluating and diagnosing conditions affecting the spine or nerve roots. Experiencing symptoms along a specific dermatome can help inform doctors about which area of the spine may be affected.