Motor: Innervates the muscles in the anterior compartment of the arm – the coracobrachialis, biceps brachii and the brachialis
Sensory: Gives rise to the lateral cutaneous nerve of forearm, which innervates skin on the lateral surface of the forearm.
Course of Musculocutaneous Nerve
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, and therefore contains fibres from C5, C6 and C7.
It leaves the axilla, and pierces the coracobrachialis muscle, near its point of insertion on the humerus. Then it passes down the arm, anterior to the brachialis muscle and posterior to the biceps brachii, innervating them both. The musculocutaneous nerve emerges laterally to the biceps tendon ,and continues into the forearm as the lateral cutaneous nerve of forearm.
The muscles in the anterior compartment of the arm are innervated – biceps brachii, brachialis and coracobrachialis. (To remember these, BBC is a useful abbreviation) These muscles flex the upper arm at the shoulder and the elbow, and the biceps brachii also performs supination of the forearm.
Sensory supply to the upper limb is provided via the lateral cutaneous nerve of forearm. The diagram below shows the area that this nerve innervates:
Clinical Relevance: Lesions of the Musculocutaneous Nerve
How it commonly occurs: An injury to the musculocutaneous nerve is relatively uncommon, as it is protected within the axilla. The most common cause of a lesion of the musculocutaneous nerve is from a stabbing.
Motor functions: The coracobrachialis, biceps brachii and brachialis muscles are paralysed. Flexion at the shoulder is weakened, but can still occur due to the pectoralis major. Flexion at the elbow is also affected, but can still be performed because of the brachioradialis muscle. Also, supination of the affected limb is greatly weakened, but is produced by the supinator muscle
Sensory functions: Loss of sensation over the lateral side of the the forearm.