Dermatomes Of Body: What You Should To Know? | Sciatic Nerve Dermatome

A dermatome in your body is an area of your skin that sends signals to the brain through the spinal nerves. These signals give rise to responses involving temperature, pressure, and pain.

Why are dermatomes important, and how many are there, and where can they be found? Continue reading to get answers to these questions and more.

Table of Contents

Your spinal nerves

The spinal nerves are divided into five groups.

The 5 groups and their points of exit from the spine are:

  1. Cervical nerves: This exit the neck region and are labeled C1–C8.
  2. Thoracic nerves: This exit the torso region and are labeled T1–T12.
  3. Lumbar nerves: This exit the lower back region and are labeled L1–L5.
  4. Sacral nerves: This exit the base of the spine and are labeled S1–S5.
  5. A coccygeal nerve pair: This exits the tailbone or coccyx. 

Locations of the dermatomes

Your dermatomes are counted based on which spinal nerve they respond to. Below, we’ll describe each dermatome and the area of the body that it’s connected with.

Cervical nerves and their dermatomes

  • C2: Base of a skull, behind the ear
  • C3: Back of the head and upper neck
  • C4: Lower neck and upper shoulders
  • C5: Upper shoulders and two collarbones
  • C6: Upper forearms and thumbs and index fingers
  • C7: Upper back, backs of arms, and middle fingers
  • C8: Upper back, inner arms, and ring and pinky fingers

Thoracic spinal nerves

  • T1: Upper chest and the back, armpit, front of the arm
  • T2: Upper chest and the back
  • T3: Upper chest and the back
  • T4: Upper chest (area of nipples) and the back
  • T5: Mid-chest and the back
  • T6: Mid-chest and the back
  • T7: Mid-chest and the back
  • T8: Upper abdomen and the mid-back
  • T9: Upper abdomen and the mid-back
  • T10: Abdomen (area of belly button) and the mid-back
  • T11: Abdomen and the mid-back
  • T12: Lower abdomen and the mid-back

Lumbar spinal nerves

  • L1: Lower back, hips, groin
  • L2: Lower back, front, and inside of the thigh
  • L3: Lower back, front, and inside of the thigh
  • L4: Lower back, front of thigh, calf, knee, inside of the ankle
  • L5: Lower back, front and outside of the calf, top, and bottom of the foot, first four toes

Sacral spinal nerves

  • S1: Lower back, back of the thigh, back and inside of the calf, last toe
  • S2: Buttocks, genitals, back of the thigh, and calf
  • S3: Buttocks, genitals
  • S4: Buttocks
  • S5: Buttocks

Sciatic nerve dermatome

The sciatic nerve is an important nerve of the lower limb. It is a flat thick band, around 2cm wide Sciatic nerve is the largest nerve in the body.

  • Nerve roots: L4-S3.
  • Motor functions:
    • Innervates the posterior thigh muscles, including the biceps femoris, semimembranosus, semitendinosus, and the hamstring part of the adductor Magnus.
    • Indirectly innervates all the muscles of the leg and foot.
  • Sensory functions: No direct sensory functions. Indirectly innervates the skin of the foot’s lateral leg, heel, and dorsal and plantar surfaces.

Importance

Dermatomes are important because they help to diagnose a variety of conditions. For instance, symptoms along a dermatome may indicate a problem with a specific nerve root in the spine.

As Example:

  • Radiculopathies: This leads to conditions in which a nerve root in the spine is pinched. Symptoms of radiculopathies can include pain, weakness, and tingling sensations. One form of radiculopathy is sciatica.
  • Shingles. Shingles is a reactivation of the varicella-zoster (chickenpox) virus that lies in the nerve roots of your body. Symptoms of shingles include pain and a rash, which occur on dermatomes associated with the affected nerve root.

Conclusion

Dermatomes can help evaluate conditions affecting the spine and nerve roots. Experiencing symptoms on a specific dermatome can help inform doctors about which spine area may be affected.

Doctors can sometimes use the severity of symptoms in a dermatome to define the location of nerve damage. Then they work to diagnose and treat the underlying cause of the damage.

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