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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.

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

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

External links

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

[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.

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