# Myotome

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{{Short description|Group of tissues}}
{{about|anatomical myotomes|myotomes in developmental biology and embryology|Myotome (embryology)}}
{{Anchor|Myosepta|Myoseptum}}
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A '''myotome''' is the group of [muscle](/source/muscle)s that a single [spinal nerve](/source/spinal_nerve) innervates.<ref>Dorland's Illustrated Medical Dictionary 2012 Page 1226</ref> Similarly a [dermatome](/source/dermatome_(anatomy)) is an area of [skin](/source/skin) that a single nerve innervates with sensory fibers. Myotomes are separated by '''myosepta''' (singular: '''myoseptum''').<ref>"Medical Definition Of MYOSEPTUM". 2018. Merriam-Webster.Com. https://www.merriam-webster.com/medical/myoseptum.</ref> In [vertebrate](/source/vertebrate) [embryonic development](/source/embryonic_development), a myotome is the part of a [somite](/source/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](/source/somite) which develops into the muscles.<ref>{{cite book|last1=Larsen|first1=William J.|title=Human embryology|date=2001|publisher=Churchill Livingstone|location=Philadelphia, Pa.|isbn=0-443-06583-7|edition=3.|page=86}}</ref>   In anatomy the myotome is the motor equivalent of a [dermatome](/source/Dermatome_(anatomy)).

==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.<ref>[http://www.apparelyzed.com/myo-dermatomes.html Apparelyzed: ''Myotomes & Dermatomes'']</ref>

===List of myotomes===
Myotome distributions of the upper and lower extremity are as follows;<ref>{{cite book|title=Orthopaedic Physical Assessment|last=Magee|first=David. J|publisher=Elsevier|year=2006|isbn=978-1-4160-3109-3|edition=4th|location=St. Louis|pages=121–181|chapter=3}}</ref><ref>{{cite book|title=Orthopaedic Physical Assessment|last=Magee|first=David. J|publisher=Elsevier|year=2009|isbn=978-1-4160-3109-3|edition=4th|location=St. Louis|pages=467–566|chapter=9}}</ref>
* [C1](/source/Cervical_spinal_nerve_1)/[C2](/source/Cervical_spinal_nerve_2): neck flexion/extension
* [C3](/source/Cervical_spinal_nerve_3): Lateral Neck Flexion
* [C4](/source/Cervical_spinal_nerve_4): shoulder elevation
* [C5](/source/Cervical_spinal_nerve_5): Shoulder abduction
* [C6](/source/Cervical_spinal_nerve_6): Elbow flexion/Wrist Extension
* [C7](/source/Cervical_spinal_nerve_7): Elbow extension/Wrist flexion
* [C8](/source/Cervical_spinal_nerve_8): Thumb extension
* [T1](/source/Thoracic_spinal_nerve_1): Finger Abduction & Adduction{{cn|date=November 2021}}
* [L1](/source/Lumbar_spinal_nerve_1)/[L2](/source/Lumbar_spinal_nerve_2): Hip Flexion
* [L3](/source/Lumbar_spinal_nerve_3): Knee extension
* [L4](/source/Lumbar_spinal_nerve_4): Ankle dorsi-flexion
* [L5](/source/Lumbar_spinal_nerve_5): Great toe extension
* [S1](/source/Sacral_spinal_nerve_1): Hip extension/Ankle plantar-flexion/ankle eversion
* [S2](/source/Sacral_spinal_nerve_2): Knee flexion
* [S3](/source/sacral_spinal_nerve_3)–[S4](/source/Sacral_spinal_nerve_4): [anal wink](/source/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](/source/isometric_exercise) resisted muscle testing, provides the clinician with information about the level in the spine where a lesion may be present.<ref>{{cite book|last=Magee|first=David. J|title=Orthopaedic Physical Assessment|year=2006|publisher=Elsevier|location=St. Louis|isbn=978-1-4160-3109-3|pages=1–63|edition=4th|chapter=1}}</ref> 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](/source/intervertebral_disc) herniation pressing on the [spinal nerve roots](/source/Posterior_root_of_spinal_nerve).

==References==
{{Reflist}}

==Further reading==
*''Neurology Textbook'', edited by Professor L. Sokolva, M.D., D.Sc. 2012, {{ISBN|9789663824260}}

==External links==
* {{EmbryologyUNSW|Notes/skmus7}}
* {{EmbryologyUNSW|Notes/week3_6}}
* {{EmbryologyUNC|mslimb|009}}

Category:Neurology

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Adapted from the Wikipedia article [Myotome](https://en.wikipedia.org/wiki/Myotome) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Myotome?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.