The brachial plexus is formed by nerve roots from which spinal segments?

Explanation

## Brachial Plexus Formation **Key Point:** The brachial plexus is formed by the union of nerve roots C5, C6, C7, C8, and T1 (the fifth cervical through first thoracic spinal nerves). ### Anatomical Origin These five nerve roots emerge from the intervertebral foramina between the cervical and thoracic vertebrae and converge to form the brachial plexus in the neck and axilla. ### Clinical Significance **High-Yield:** Injuries affecting different levels of the brachial plexus correlate with specific spinal nerve involvement: - **Upper trunk injuries** (C5–C6): Erb's palsy — loss of shoulder abduction and external rotation - **Lower trunk injuries** (C8–T1): Klumpke's palsy — loss of hand intrinsic muscles and wrist flexion - **Complete plexus injury** (C5–T1): Total arm paralysis **Mnemonic:** **CCCTT** — C5, C6, C7, C8, T1 (remember: five nerves, starting at C5, ending at T1). ### Why This Matters Knowing the exact spinal segments is essential for: - Localizing lesions based on clinical presentation - Predicting motor and sensory deficits - Planning surgical repair in traumatic injuries