What is a Dermatome? - Definition & Distribution

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  • 0:04 What Is a Dermatome?
  • 1:01 Mapping the Spinal Cord
  • 2:20 Examples of Conditions
  • 3:15 Lesson Summary
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Lesson Transcript
Instructor: Rachel Torrens
The human body is divided into multiple skin zones known as dermatomes. In this lesson, learn all about dermatomes, including their relationship to the spinal cord and distribution on the body.

What Is a Dermatome?

If you tilt your chin towards your chest, then reach up and press on the base of your neck, you should be able to feel a hard bony lump. Well, that is one vertebra in your spine! Specifically it's the seventh cervical vertebra, known briefly as C7, and we'll chat more about it later.

Your spine is comprised of over thirty different vertebrae, which are categorized based on location. Moving from your neck down to your tailbone the categories are: cervical, thoracic, lumbar, and sacral.

Each vertebra houses a specific spinal nerve that innervates a particular part of the skin known as a dermatome. There are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, and 5 sacral nerves. All of these nerves, except the first cervical nerve (C1), are wired to a specific dermatome, sending messages from a specific area of skin on the body to the brain.

Mapping the Spinal Cord

These dermatomes provide a rough map, useful for healthcare professionals and researchers. The dermatomes, like the spinal nerves, are divided into four sections: cervical, thoracic, lumbar, and sacral. Each dermatome is labeled according to the spinal nerve which innervates it. So, the dermatome innervated by the seventh cervical nerve would be dermatome C7. Remember the bony lump you felt at the back of your neck? Running through that vertebra is spinal nerve C7, which reaches out to innervate the skin of the shoulder, upper arm, lower arm, index and ring fingers!

There are four major categories of dermatomes:

  • The cervical dermatomes cover skin on the back of the head, neck, shoulders, arms and hands

  • The thoracic dermatomes cover skin on the inner arm, chest, abdomen, and mid-back

  • The lumbar dermatomes cover skin on the lower back, fronts of the legs, outer thighs and outer calves, and tops and bottoms of the feet

  • The sacral dermatomes cover skin on the genital and anal regions; back of the legs, central back of the thighs and calves; and the outer edge of the feet

These dermatomes have been discovered mainly through clinical observations over the years, though it's important to realize they are just a guideline. Every human is wired slightly differently, and variations in the exact dermatome borders is expected.

Examples of Conditions

Dermatomes help in the diagnosis and treatment of several conditions. These conditions include:

  1. Viral illnesses
  2. Radiculopathy
  3. Spinal cord injuries

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