Musculocutaneous

Musculocutaneous nerve is a major peripheral nerve of the upper limb. It arises from the lateral cord of the brachial plexus, typically containing fibers from spinal nerves C5 to C7. The nerve exits the axilla and pierces the coracobrachialis muscle, then descends between the biceps brachii and brachialis in the anterior compartment of the arm. It provides motor innervation to three muscles: coracobrachialis, biceps brachii, and brachialis, contributing to elbow flexion and, in the case of the biceps, forearm supination.

Distally, the musculocutaneous nerve continues as the lateral antebrachial cutaneous nerve, which supplies sensation to the lateral (radial) aspect of the forearm. This cutaneous branch typically continues after the elbow, separating sensory function from motor control in the arm.

Clinical significance centers on injury or compression of the nerve, which can lead to weakness or loss of elbow flexion and forearm supination, along with sensory loss on the lateral forearm. The biceps reflex may be diminished, reflecting involvement at the C5–C6 level. Common etiologies include trauma or compression in the upper arm, shoulder dislocations, or midshaft humeral fractures, as well as iatrogenic injury during surgical procedures in the region.

Anatomic variations exist, including occasional contributions from other roots and communications with adjacent nerves such as the median nerve. Despite variability, the musculocutaneous nerve remains identified by its course from the lateral cord, piercing the coracobrachialis, and its role in motor control of elbow flexors and sensory innervation of the lateral forearm.