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A myotome is the group of muscles that a single spinal nerve innervates. [1] Similarly a dermatome is an area of skin that a single nerve innervates with sensory fibers. Myotomes are separated by myosepta (singular: myoseptum). [2] In vertebrate embryonic development, a myotome is the part of a somite that develops into muscle.



The anatomical term myotome which describes the muscles served by a spinal nerve root, is also used in embryology to describe that part of the somite which develops into the muscles. [3] In anatomy the myotome is the motor equivalent of a dermatome.


Each muscle in the body is supplied by one or more levels or segments of the spinal cord and by their corresponding spinal nerves. A group of muscles innervated by the motor fibres of a single nerve root is known as a myotome. [4]

List of myotomes

Myotome distributions of the upper and lower extremity are as follows; [5] [6]

Clinical significance

In humans myotome testing can be an integral part of neurological examination as each nerve root coming from the spinal cord supplies a specific group of muscles. Testing of myotomes, in the form of isometric resisted muscle testing, provides the clinician with information about the level in the spine where a lesion may be present. [7] During myotome testing, the clinician is looking for muscle weakness of a particular group of muscles. Results may indicate lesion to the spinal cord nerve root, or intervertebral disc herniation pressing on the spinal nerve roots.

See also

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Myotome is the group of muscles that a single spinal nerve root innervates.


  1. Dorland's Illustrated Medical Dictionary 2012 Page 1226
  2. "Medical Definition Of MYOSEPTUM". 2018. Merriam-Webster.Com.
  3. Larsen, William J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p. 86. ISBN   0-443-06583-7.
  4. Apparelyzed: Myotomes & Dermatomes
  5. Magee, David. J (2006). "3". Orthopaedic Physical Assessment (4th ed.). St. Louis: Elsevier. pp. 121–181. ISBN   978-1-4160-3109-3.
  6. Magee, David. J (2009). "9". Orthopaedic Physical Assessment (4th ed.). St. Louis: Elsevier. pp. 467–566. ISBN   978-1-4160-3109-3.
  7. Magee, David. J (2006). "1". Orthopaedic Physical Assessment (4th ed.). St. Louis: Elsevier. pp. 1–63. ISBN   978-1-4160-3109-3.

Further reading