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. In vertebrate embryonic development, a myotome is the part of a somite that develops into the muscles.


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.[2] In anatomy the myotome is the motor equivalent of a dermatome. Myotomes are separated by myosepta.[3]


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]

  • C1/C2: neck flexion/extension
  • C3: neck lateral flexion
  • C4: shoulder elevation
  • C5: shoulder abduction
  • C6: elbow flexion
  • C7: elbow extension/wrist flexion/finger extension
  • C8: finger flexion
  • T1: finger abduction
  • L2: hip flexion
  • L3: knee extension
  • L4: ankle dorsi-flexion
  • L5: great toe extension
  • S1: ankle plantar-flexion/ankle eversion/hip extension
  • S2: knee flexion
  • S3S4: anal wink

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


  1. Dorland's Illustrated Medical Dictionary 2012 Page 1226
  2. Larsen, William J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p. 86. ISBN 0-443-06583-7.
  3. "Medical Definition Of MYOSEPTUM". 2018. Merriam-Webster.Com.
  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.

neurology textbook, edited by Professor L. Sokolva, M.D., D.Sc. 2012, ISBN 9789663824260

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