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Myotomes
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A myotome is the group of muscles that a single spinal nerve innervates. Most muscles are innervated by more than one spinal nerve root, and therefore consist of multiple myotomes.
Simplified Examination
Spinal Level | Movement |
---|---|
Upper Limb | |
C5 | Shoulder abduction |
C6 | Elbow flexion |
C7 | Elbow extension |
C8 | Finger flexion |
T1 | Finger abduction |
Lower Limb | |
L2 | Hip flexion |
L3 | Hip adduction |
L4 | Knee extension |
L5 | Ankle dorsiflexion |
S1 | Ankle plantarflexion |
Commonly Tested Movements
Movement | UMN | Root | Reflex | Nerve | Muscle |
---|---|---|---|---|---|
Upper Limb | |||||
Shoulder abduction | ++ | C5 | Axillary | Deltoid | |
Elbow flexion | C5/6 C6 |
+ + |
Musculocutaneous Radial |
Biceps Brachioradialis | |
Elbow extension | + | C7 | + | Radial | Triceps |
Radial wrist extension | + | C6 | Radial | Extensor carpi radialis longus | |
Finger extension | + | C7 | Posterior interosseous nerve | Extensor digitorum communis | |
Finger flexion | C8 |
+ |
Anterior interosseous nerve Ulnar |
Flexor pollicis longus and flexor digitorum profundus (index) Flexor digitorum profundus (ring and little) | |
Finger abduction | ++ |
T1 T1 |
Ulnar Median |
First dorsal interosseous Abductor pollicis brevis | |
Lower Limb | |||||
Hip flexion | ++ | L1/2 | Iliopsoas | ||
Hip adduction | L2/3 | + | Obturator | Adductors | |
Hip extension | L5/S1 | Sciatic | Gluteus Maximus | ||
Knee flexion | + | S1 | Sciatic | Hamstrings | |
Knee extension | L3/4 | + | Femoral | Quadriceps | |
Ankle dorsiflexion | ++ | L4 | Deep peroneal | Tibialis anterior | |
Ankle eversion | L5/S1 | Superficial peroneal | Peronei | ||
Ankle plantarflexion | S1/S2 | + | Tibial | Gastrocnemius, soleus | |
Big toe extension | L5 | Deep peroneal | Extensor hallucis longus |
Complete Myotome Chart
Muscle | Nerve | Spinal Roots | ||||||
---|---|---|---|---|---|---|---|---|
Upper Limb [3][2] | ||||||||
C3 | C4 | C5 | C6 | C7 | C8 | T1 | ||
Trapezius | Spinal accessory nerve | ๐ฒ | ๐ฒ | |||||
Supraspinatus, infraspinatus | Suprascapular nerve | ๐ฆ | ๐ฒ | |||||
Pectoralis major | Lateral and medial pectoral nerves | ๐ฒ | ๐ฒ | ๐ฒ | ๐ฒ | |||
Latissimus dorsi | Thoracodorsal nerve | ๐ฒ | ๐ฆ | ๐ฒ | ||||
Teres major | Lower subscapular nerve | ๐ฒ | ๐ฒ | ๐ฒ | ||||
Serratus anterior | Long thoracic nerve | ๐ฒ | ๐ฒ | ๐ฒ | ||||
Rhomboids | Dorsal scapular nerve | ๐ฒ | ๐ฒ | |||||
Deltoid | Axillary nerve | ๐ฒ | ๐ฒ | |||||
Biceps and brachialis | Musculocutaneous nerve | ๐ฒ | ๐ฒ | |||||
Triceps | Radial nerve | ๐ฒ | ๐ฆ | ๐ฒ | ||||
Brachioradialis | ๐ฒ | ๐ฆ | ||||||
Wrist extensors (radial) | ๐ฆ | ๐ฒ | ||||||
FCR, pronator teres | Median nerve | ๐ฒ | ๐ฒ | |||||
FDS, Thenar | ๐ฒ | ๐ฆ | ||||||
FPL, FDP, PQ | Anterior interosseous nerve | ๐ฒ | ๐ฆ | ๐ฒ | ||||
EDC, EPL | Posterior interosseous nerve | ๐ฆ | ๐ฒ | ๐ฒ | ||||
FCU | Ulnar nerve | ๐ฒ | ๐ฆ | ๐ฒ | ||||
FDP radial digits | ๐ฆ | ๐ฒ | ||||||
FDP ulnar digits | ๐ฒ | ๐ฆ | ๐ฒ | |||||
Interossei | ๐ฒ | ๐ฒ | ๐ฆ | |||||
Lower Limb [2] | ||||||||
L1 | L2 | L3 | L4 | L5 | S1 | S2 | ||
Iliopsoas | Femoral nerve | ๐ฆ | ๐ฆ | ๐ฒ | ||||
Quadriceps femoris | ๐ฒ | ๐ฆ | ๐ฆ | |||||
Adductor longus and magnus | Obturator nerve | ๐ฆ | ๐ฆ | ๐ฒ | ||||
Gluteus medius, minimis, tensor fascia lata | Superior gluteal nerve | ๐ฆ | ๐ฆ | ๐ฒ | ||||
Gluteus maximus | Inferior gluteal nerve | ๐ฆ | ๐ฆ | ๐ฒ | ||||
Semitendinosus, biceps femoris, semimembranosus | Sciatic and tibial nerves | ๐ฒ | ๐ฆ | ๐ฒ | ||||
Gastrocnemius and soleus | ๐ฒ | ๐ฒ | ||||||
Tibialis posterior | ๐ฒ | ๐ฒ | ||||||
Flexor digitorum longus | ๐ฒ | ๐ฆ | ๐ฆ | |||||
Abductor hallucis, abductor digiti minimi, interossei | ๐ฒ | ๐ฒ | ||||||
Tibialis anterior | Sciatic and common peroneal nerves | ๐ฆ | ๐ฒ | |||||
Extensor digitorum longus, extensor hallucis longus | ๐ฆ | ๐ฒ | ||||||
Extensor digitorum brevis, peroneus longus, peroneus brevis | ๐ฒ | ๐ฒ |
Myotome Dance
Spinal Levels | Memory Aid | Action |
---|---|---|
Upper Limb | ||
C1, 2 | I nod to you | Neck flexion/extension |
C3 | Donโt tickle me | Neck lateral flexion |
C4 | Iโm not sure | Shoulder elevation |
C5 | Feel alive | Shoulder flexion, abduction, & lateral rotation |
C6, 7, 8 | Close the gate | Shoulder extension, adduction & medial rotation |
C5, 6 | Pick up sticks | Elbow flexion |
C7, 8 | Lay them straight | Elbow extension |
C5, 6 | Flick my wrists | Forearm supination |
C7, 8 | The time is late | Forearm pronation |
C6, 7 | Fly up to heaven | Wrist flexion & extension |
C7 | Paper | Finger extension |
C8 | Rock | Finger flexion (though some sources say C7, 8 does both finger extension and flexion) |
T1 | Scissors | Finger abduction & adduction |
Lower Limb | ||
L2, 3 | Lift my knee | Hip flexion |
L3, 4 | Kick the door | Knee extension (& knee-jerk reaction) |
L4, 5 | Foot points to the sky | Ankle dorsiflexion |
L4, 5 | Extend my thigh | Hip extension |
L5, S1, (S2) | Kick my bum (Run to poo) | Knee flexion |
S1, 2 | Stand on my shoes | Ankle plantarflexion (& ankle jerk) |
L2, 3, 4 | Modestly close the door | Hip adduction & internal/medial rotation |
L4 - S2 | The opposite is true | Hip abduction & external/lateral rotation |
C3, 4, 5 | Keeps the diaphragm alive | Innervates the diaphragm |
S2, 3, 4 | Keeps poo off the floor | Innervates bowel, bladder, sex organs, anal sphincter, pelvic muscles. (& anal wink reflex) |
Note
- T1-12 Supplies chest wall and abdominal muscles
- L1 Contributes to hip flexion & adduction
- L5, S1, S2 Babinski plantar reflex/extensor response in UMN lesion
Other Videos
References
- โ The Noted Anatomist. Myotomes. Feb 29, 2020. Available on youtube
- โ 2.0 2.1 2.2 Brain. Aids to the Examination of the Peripheral Nervous System, 4th edition. 2000
- โ Bell et al.. Refinement of myotome values in the upper limb: Evidence from brachial plexus injuries. The surgeon : journal of the Royal Colleges of Surgeons of Edinburgh and Ireland 2017. 15:1-6. PMID: 26409623. DOI.