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

Simplified myotomes[1]
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

Commonly tested movements. UMN column are movements that are preferentially weak in UMN lesions[2]
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

Complete Myotome Chart
Muscle Nerve Spinal Roots
Upper Limb [3][2][4]
C3 C4 C5 C6 C7 C8 T1
Trapezius Spinal accessory nerve πŸ”² πŸ”²
Supraspinatus, infraspinatus Suprascapular nerve πŸ”³ πŸ”²
Pectoralis major Lateral and medial pectoral nerves πŸ”² πŸ”² πŸ”² πŸ”²
Latissimus dorsi Thoracodorsal nerve πŸ”² πŸ”³ πŸ”²
Teres major Lower subscapular nerve πŸ”² πŸ”² πŸ”²
Serratus anterior Long thoracic nerve πŸ”² πŸ”² πŸ”²
Rhomboids Dorsal scapular nerve πŸ”² πŸ”²
Deltoid Axillary nerve πŸ”² πŸ”²
Biceps and brachialis Musculocutaneous nerve πŸ”² πŸ”²
Triceps Radial nerve πŸ”² πŸ”³ πŸ”²
Brachioradialis πŸ”² πŸ”³
ECRL πŸ”² πŸ”³ πŸ”²
ECU πŸ”³ πŸ”²
Finger extensors πŸ”² πŸ”²
FCR, pronator teres Median nerve πŸ”² πŸ”²
FDS πŸ”² πŸ”³
APB πŸ”² πŸ”²
FPL, FDP, PQ Anterior interosseous nerve πŸ”² πŸ”³ πŸ”²
EDC, EPL Posterior interosseous nerve πŸ”³ πŸ”² πŸ”²
FCU Ulnar nerve πŸ”² πŸ”³ πŸ”²
FDP radial digits πŸ”³ πŸ”²
FDP ulnar digits πŸ”² πŸ”³ πŸ”²
Interossei πŸ”² πŸ”² πŸ”³
Lower Limb [2][4]
L1 L2 L3 L4 L5 S1 S2
Iliopsoas Femoral nerve πŸ”³ πŸ”³ πŸ”²
Quadriceps femoris πŸ”² πŸ”³ πŸ”³
Adductor longus and magnus Obturator nerve πŸ”³ πŸ”³ πŸ”²
Gluteus medius, minimis, tensor fascia lata Superior gluteal nerve πŸ”³ πŸ”³ πŸ”²
Gluteus maximus Inferior gluteal nerve πŸ”³ πŸ”³ πŸ”²
Semitendinosus, biceps femoris, semimembranosus Sciatic nerve trunk† πŸ”² πŸ”³ πŸ”²
Tibialis posterior Tibial nerve† πŸ”² πŸ”²
Gastrocnemius and soleus πŸ”² πŸ”²
Flexor digitorum longus πŸ”² πŸ”³ πŸ”³
Tibialis anterior Peroneal nerve† πŸ”³ πŸ”²
Extensor digitorum longus, extensor hallucis longus πŸ”³ πŸ”²
Abductor hallucis, abductor digiti minimi, interossei πŸ”² πŸ”²
Extensor digitorum brevis, peroneus longus, peroneus brevis πŸ”² πŸ”²
πŸ”² segmental contribution, πŸ”³ significant segmental contribution.

† The sciatic nerve trunk divides above the knee into the peroneal and tibial nerves, therefore lesions of the sciatic nerve trunk affect the muscles of all three branches.

Myotome Dance

Myotome Dance
Spinal Levels Memory Aid Action
Upper Limb
C1, 2 I nod to you Neck flexion/extension
C3 Don’t tickle me Neck lateral flexion
C4 I’m 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

  1. ↑ The Noted Anatomist. Myotomes. Feb 29, 2020. Available on youtube
  2. ↑ 2.0 2.1 2.2 Brain. Aids to the Examination of the Peripheral Nervous System, 4th edition. 2000
  3. ↑ 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.
  4. ↑ 4.0 4.1 McGee, Steven R. Evidence-based physical diagnosis. Philadelphia, PA: Elsevier, 2018.