Myotome

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

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.

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[citation needed]
  • 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.

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