Which myotome is responsible for elbow flexion?

Explanation

## Upper Limb Myotomes and Motor Function ### Myotome Definition A myotome is a group of muscles innervated by a single spinal nerve root. Understanding myotomes is essential for localizing spinal cord and nerve root lesions. **Key Point:** Elbow flexion is primarily mediated by the **C5–C6 myotome**, with the biceps brachii being the main agonist (innervated by the musculocutaneous nerve from C5–C6). ### Upper Limb Myotome Map | Myotome | Primary Motor Function | Key Muscles | Nerve | |---------|------------------------|-------------|-------| | **C5–C6** | **Elbow flexion** | **Biceps brachii, brachialis** | **Musculocutaneous** | | C6–C7 | Wrist extension | Extensor carpi radialis longus/brevis | Radial | | C7–C8 | Wrist flexion, finger extension | Flexor carpi radialis, extensor digitorum | Radial, ulnar | | C8–T1 | Finger flexion, intrinsic hand muscles | Flexor digitorum profundus, lumbricals | Ulnar, median | **High-Yield:** The C5–C6 myotome is tested frequently because: - Cervical radiculopathy at C5–C6 causes weakness of elbow flexion (positive finding on examination) - Axillary nerve injury (C5–C6) causes loss of shoulder abduction and elbow flexion weakness - C5–C6 nerve root compression is the most common cervical radiculopathy in clinical practice **Clinical Pearl:** When examining a patient with suspected cervical radiculopathy, testing elbow flexion against resistance (C5–C6 strength) is one of the first motor tests performed. Loss of elbow flexion strength strongly suggests C5–C6 nerve root involvement. **Mnemonic:** "**C5–C6: Curl up**" — Remember that elbow flexion (curling the arm) is C5–C6, just as you would curl up when cold at the C5–C6 level. [cite:Clinically Oriented Anatomy by Moore, 8e Ch 7]