Resident Editor: Anita Hargrave, M.D., Talia Kahn, M.D., M.P.H.
Faculty Editor: Vanja Douglas, M.D.
Background
Spinal nerves are composed of ventral and dorsal roots. The ventral roots primarily carry motor outflow axons and autonomic fibers. Typically, several adjacent spinal roots innervate each muscle. The table below lists specific muscles and their associated nerve root(s). For each set of nerve roots, the levels that are bolded are the dominant nerve roots.
The sensation is transmitted through the dorsal roots, each of which innervates a well-defined portion of the skin known as a dermatome. Dermatomal territories often overlap making it difficult to determine the affected nerve with certainty based on sensory testing alone. Key dermatomes include C6 (thumb), C7 (middle finger), C8 (fifth digit), T4 (nipple line), and T10 (umbilicus).
|
Muscle and Function |
Spinal Nerve Root/ Nerve |
Sensory Distribution |
Reflex Loss |
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Diaphragm: respiration
|
C3, C4, C5: phrenic nerve |
C4: shoulder and clavicle |
|
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Deltoid: arm abduction
|
C5, C6: axillary nerve |
C5: lateral upper arm |
|
|
Biceps: forearm flexion |
C5, C6: musculocutaneous nerve |
C6: lateral forearm, thumb, 2nd digit |
Biceps (C5, C6) |
|
Brachioradialis: forearm flexion |
C5, C6: radial nerve |
|
Brachio-radialis (C5, C6) |
|
Triceps: forearm extension |
C6, C7, C8: radial nerve |
C7: 3rd digit |
Triceps (C7) |
|
Extensor digitorum communis: finger extension |
C7, C8: radial nerve (posterior interosseous) |
|
|
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Flexor digitorum superficialis: finger flexion |
C7, C8, T1: median nerve |
C8: 4th and 5th digit |
Finger flexor (C8) |
|
First dorsal interosseous: index finger abduction |
C8, T1: ulnar nerve |
T1: medial forearm |
|
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Iliopsoas: hip flexion |
L2, L3: femoral nerve and plexus |
L2: anterior, medial, and lateral upper thigh |
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Quadriceps femoris: knee extension |
L2, L3, L4: femoral nerve |
L3: anterior and medial lower thigh including knee |
Patellar ( L3, L4) |
|
Hamstrings: knee flexion |
L4, L5, S1: sciatic nerve |
|
|
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Tibialis anterior: dorsiflexion of the foot |
L4, L5: sciatic nerve (deep peroneal) |
L4: medial calf |
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Extensor hallucis longus: dorsiflexion of great toe |
L4, L5, S1: sciatic nerve (deep peroneal) |
L5: lateral shin and calf, 2nd, 3rd, and 4th toes |
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|
Gastrocnemius: plantar flexion of foot |
L5, S1, S2: sciatic nerve (tibial) |
S1: lateral ankle, 5th toe, sole of the foot; S2: posterior calf and thigh |
Achilles (S1, S2) |
References
Waxman SG. Chapter 5 The Spinal Cord. In: Waxman SG, ed. Clinical Neuroanatomy. 28th ed. New York: McGraw-Hill; 2017. http://www.accessmedicine.com/content.aspx?aID= 147036139. Accessed 4/15/2018.
Waxman SG. Appendix B. Testing Muscle Function. In: Waxman SG, ed. Clinical Neuroanatomy. 28th ed. New York: McGraw-Hill; 2017. http://www.accessmedicine.com/ content.aspx?aID= 147034019. Accessed 4/15/2018.
Waxman SG. Appendix C. Spinal Nerves and Plexuses. In: Waxman SG, ed.Clinical Neuroanatomy. 28th ed. New York: McGraw-Hill; 2017. http://www.accessmedicine.com/content.aspx?aID=147034080. Accessed 4/15/2018.