From the Research
The nerve root of the biceps brachii muscle is primarily C5-C6 from the brachial plexus, specifically via the musculocutaneous nerve, as confirmed by the most recent study 1. This means that the fifth and sixth cervical spinal nerves provide the main innervation to the biceps muscle. The musculocutaneous nerve branches from the lateral cord of the brachial plexus and travels through the coracobrachialis muscle before reaching the biceps. This nerve supplies both motor function, allowing the biceps to flex the elbow and supinate the forearm, and sensory information from the muscle. Some key points to consider include:
- The C5 root predominantly innervates both deltoid and biceps brachii in patients with symptomatic cord lesions at the C4-C5 intervertebral level, as shown in a study from 2004 2.
- The functional motor innervation of brachial plexus roots was examined in a study from 1996, which found that C6 mainly constructs the musculocutaneous nerve to innervate biceps muscle 3.
- A study from 2024 found that transfer of the ipsilateral C7 nerve root to the upper trunk can be an effective option for the functional reconstruction of the shoulder and elbow after C5-C6 brachial plexus injuries 1. Understanding this innervation pattern is clinically important when assessing upper limb neurological function, as biceps weakness or abnormal reflexes may indicate pathology at the C5-C6 level of the spinal cord or along the course of the musculocutaneous nerve. During physical examination, the biceps reflex specifically tests the integrity of the C5-C6 nerve roots, making it a valuable diagnostic tool for cervical radiculopathy or other neurological conditions affecting this region. Other studies have explored alternative treatments, such as one-fascicle median nerve transfer to the biceps muscle in C5 and C6 root avulsions of brachial plexus injury, which have shown promising results 4.