The musculocutaneous nerve is a mixed branch of the lateral cord of the brachial plexus derived from cervical spinal nerves C5-C7. It arises opposite the lower border of the pectoralis major. It provides motor innervation to the muscles of the anterior compartment of the arm: the coracobrachialis, biceps brachii, and brachialis. It provides sensory innervation to the lateral forearm (via its terminal branch). It courses through the anterior part of the arm, terminating 2 cm above elbow; after passing the lateral edge of the tendon of biceps brachii it is becomes known as the lateral cutaneous nerve of the forearm. Structure Course Musculocutaneous nerve arises from the lateral cord of the brachial plexus with root value of C5 to C7 of the spinal cord. It follows the course of the third part of the axillary artery (part of the axillary artery distal to the pectoralis minor) laterally and enters the frontal aspect of the arm where it penetrates the coracobrachialis muscle. It then passes downwards and laterally between the biceps brachii (above) and the brachialis muscles (below), to the lateral side of the arm; at 2 cm above the elbow it pierces the deep fascia lateral to the tendon of the biceps brachii and is continued into the forearm as the lateral cutaneous nerve of the forearm. Distribution Motor innervation In its course through the arm it innervates the coracobrachialis, biceps brachii, and the greater part of the brachialis. Sensory innervation Its terminal branch, the lateral cutaneous nerve of the forearm, supplies the sensation of the lateral side of the forearm from the elbow to the wrist. The musculocutaneous nerve also gives articular branches to the elbow joint and to the humerus. Variation The musculocutaneous nerve presents frequent variations and communications with the median nerve. It may adhere for some distance to the median and then pass outward, beneath the biceps brachii, instead of through the coracobrachialis. Some of the fibers of the median may run for some distance in the musculocutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous. The nerve may pass under the coracobrachialis or through the biceps brachii. Occasionally it gives a filament to the pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent. Nerve injuries