What are dermatomes and why they matter

Dermatomes are areas of skin that get sensation from specific spinal nerve roots. These nerves send signals like pressure, pain, temperature, and texture from your skin to your spinal cord, and then to your brain.

Spinal nerves exist in 31 pairs, on each side of the spine. A nerve root is a bundle of nerve fibers that branch off the spinal cord and pass through the opening between the two vertebrae. Vertebrae are the small bones that make up the spine.

From there, the nerves travel through your torso, arms, and legs. They make up the peripheral nervous system. These nerves provide sensory (sensory-based) information, motor function (motor), and other functions.

Although the body has 31 spinal nerves, you only have 30 dermatomes. This is because the highest spinal nerve in the neck, called cervical 1 (C1), does not provide sensory function.

Leather knife set

Dermatomes are divided into groups according to where they originate in the spine:

  • Cervical nerves: There are eight pairs of nerves in the neck, numbered C1 to C8. Since C1 has no sensory function, you have seven cervical dermatomes.
  • Thoracic nerves: The trunk has 12 pairs, numbered T1 to T12. You have 12 chest dermatomes.
  • Lumbar nerves: There are five pairs in the lower back, numbered L1 to L5. You have five waist dermatomes.
  • Sacral nerves: The sacrum (part of the pelvis) has five pairs, numbered S1 through S5. You have five sacral dermatomes.
  • Coccygeal Nerve: The coccyx (coccyx) region has a pair, so you have a coccygeal dermatome.

The lumbar, sacral, and coccygeal dermatomes are often grouped together and are referred to as “lower extremity dermatomes.”

Anatomy of the Spinal Nerve

Place

The exact location of the dermatomes varies from person to person because nerves in certain areas may overlap. However, skin slice maps are a good guide for where they are in most people.

On the trunk, dermatomes are horizontal stripes stacked on top of each other. However, they are a combination of angular and straight stripes on your arms and legs.

cervical nerve and dermatome

The seven dermatomes associated with the cervical nerve are:

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  • C2: behind the ear and at the base of the skull
  • C3: Back of head and neck
  • C4: Through the lower neck and top of the shoulders
  • C5: Through the collarbone and upper shoulder
  • C6: Shoulder, outer arm and thumb
  • C7: Upper back, back of arm, index and middle fingers
  • C8: upper back, inner arm, ring and pinky fingers

Thoracic nerve and dermatome

Thoracic dermatomes travel down from where their nerves emerge from the spine and around the trunk.

The first nine form relatively straight lines at the chest, while the lower ones slope down in the middle. The 12 dermatomes associated with the thoracic nerve are:

  • T1: Through the upper back and chest, through the armpits, down the front of the arms
  • T2: Across the upper back and chest, just below the armpits
  • T3: Across the upper back and chest, just above the nipples
  • T4: Across the upper back and chest, including the nipples
  • T5, T6, T7, narrow band in the mid-back and chest, starting under the nipple
  • T8, T9: Narrow bands on the mid-back and upper abdomen, ending just above the navel
  • T10: Mid back and abdomen, including navel
  • T11: Mid back and just below belly button, pelvis tilted forward
  • T12: Mid back and lower abdomen, more severe forward pelvic tilt

Lumbar nerves and dermatomes

The lumbar dermatomes also travel down from where the nerves leave the spine, and they continue down as they pass around the hip.

The five dermatomes associated with lumbar nerve roots are:

  • L1: Through the lower back, around the hips, and down to the groin
  • L2, L3: Through the lower back, down through the front and inner thighs
  • L4: Through the lower back, leaning down from the front of the thighs, knees, and calves and wrapping around the inside of the ankle
  • L5: Through the lower back, sloping down from the anterolateral calf, feet (top and bottom), and first four toes

Sacral nerves and dermatomes

The sacral dermatomes associated with the five sacral nerves are:

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  • S1: Cross the lowest part of the back, then arch steeply, along the back of the thigh, the back of the calf, and the inner side, all the way to the little toe
  • S2: Genitals in front, over buttocks in back, then sharply arched down the back of thighs and calves
  • S3: An egg-shaped area behind the buttocks, with the genitals in front
  • S4: Smaller egg-shaped area of ​​the buttocks
  • S5: A small spot on the hip

tail nerve and dermatome

The final dermatome and individual spinal nerves in the coccygeal region affect the gluteal region and the coccygeal region.

Why Skin Diseases Matter

In clinical practice, dermatomes are important in helping physicians determine the origin of neurological problems and diagnose certain diseases.

shingles

Shingles, also known as shingles, is the result of reactivation of the varicella-zoster virus, which causes chickenpox. Once you have chickenpox, the virus stays in your body forever, dormant in a group of nerve fibers between the vertebrae called the dorsal root ganglion.

When the virus becomes active later in life, it can cause shingles. This is a painful, itchy, or tingling rash. It can also cause headaches, sensitivity to bright light, and discomfort for days before the rash appears.

The rash is most common on the chest dermatome. If it is in one or two adjacent dermatomes, it is called localized shingles. When it spreads to three or more of these sensory areas, it’s called disseminated shingles.

Doctors suspect shingles if they see a linear rash that follows a dermatome pattern, especially if the patient is known to have chickenpox. To confirm the diagnosis, they usually test the fluid in the blisters or cell debris to see if the virus is present.

What is the link between shingles and immunosuppression?

Disseminated shingles occurs almost exclusively in people with suppressed or compromised immune systems. Indistinguishable from chicken pox.

trauma

Dermatomes are particularly useful for determining the location of injury in spinal cord injuries. Doctors examine one dermatome at a time during the exam.

When they determined that a specific dermatome was affected, it told them where the spinal cord injury was. For example, if someone has impaired sensory function in the back of their lower leg and little toe, it suggests that the S1 dermatome may be the site of injury.

spinal cord injury

tense nerves

Compressed nerves, also called radiculopathy, are caused by the narrowing of the nerve roots passing through the space between the vertebrae. Because nerve roots are involved, radiculopathy can cause dermatomal symptoms, including:

  • pain
  • weakness
  • loss of reflex
  • numbness
  • Tingling, tingling, and other abnormal nerve sensations

Symptoms may vary depending on the nerve root affected. The specific changes and location of symptoms can tell doctors where the radiculopathy is occurring.

How strange reactions can affect your health

generalize

Dermatomes are areas of skin that attach to specific nerve bundles. These nerve bundles provide sensation to the dermatomes. Dermatomas can help your doctor determine which part of your body is affected by certain conditions, such as shingles, injuries, and pinched nerves.

Frequently Asked Questions

  • What is a leather knife?

    Dermatomes are areas of the skin that feel the sensations of the spinal nerves. There are 30 different pairs of dermatomes on the human body, which correspond to nerves that run through the vertebrae and transmit pain, pressure, tingling or temperature sensations to different areas of the body.

  • What are some examples of skin knots?

    Sciatica is a common example of a dermatome. Sciatica is pain from the back of the thigh to the knee and may involve the S1 or S2 dermatome. Numbness and tingling in the arm may involve the C6 to C8 dermatomes.

  • Is the leather knife accurate?

    Sometimes, but not always. A study of pain patterns in damaged L5 and S1 nerve roots analyzed spinal injuries using MRI and found that 50% to 80% of the lesions corresponded to dermatomal sensation. However, the study authors note that predicting spinal injury based on dermatomal location is no more accurate than chance.