Myotome

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.

This article is about anatomical myotomes. For myotomes in developmental biology and embryology, see Myotome (embryology).

Structure

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.

Function

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: Lateral Neck Flexion
  • C4: shoulder elevation
  • C5: Shoulder abduction
  • C6: Elbow flexion/Wrist Extension
  • C7: Elbow extension/Wrist flexion
  • C8: Thumb extension
  • T1: Finger Abduction & Adduction
  • L1/L2: Hip Flexion
  • L3: Knee extension
  • L4: Ankle dorsi-flexion
  • L5: Great toe extension
  • S1: Hip extension/Ankle plantar-flexion/ankle eversion
  • S2: Knee flexion
  • S3–S4: 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

References
  1. Dorland's Illustrated Medical Dictionary 2012 Page 1226
  2. "Medical Definition Of MYOSEPTUM". 2018. Merriam-Webster.Com. https://www.merriam-webster.com/medical/myoseptum.
  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
  • Neurology Textbook, edited by Professor L. Sokolva, M.D., D.Sc. 2012, ISBN 9789663824260
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