Myotome

A myotome is the group of muscles that a single spinal nerve root 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.

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.^[2] 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.^[3]

List of myotomes

Myotome distributions of the upper and lower extremity are as follows;^[4][5]

• C1/C2: neck flexion/extension
• C3: neck lateral flexion
• C4: shoulder elevation
• C5: shoulder abduction
• C6: elbow flexion/wrist extension
• C7: elbow extension/wrist flexion
• 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
• 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.^[6] 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

• Dermatome (anatomy)
• Somite

References

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. Apparelyzed: Myotomes & Dermatomes
4. Magee, David. J (2006). "3". Orthopaedic Physocal Assessment (4th ed.). St. Louis: Elsevier. pp. 121–181. ISBN 978-1-4160-3109-3.
5. Magee, David. J (2009). "9". Orthopaedic Physocal Assessment (4th ed.). St. Louis: Elsevier. pp. 467–566. ISBN 978-1-4160-3109-3.
6. 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 : sokolva ,M,D.D,.SC 2012 ,ISBN 9789663824260

External links

• Embryology at UNSW Notes/skmus7
• Embryology at UNSW Notes/week3_6
• mslimb-009—Embryo Images at University of North Carolina