The Musculocutaneous Nerve

The musculocutaneous nerve is a major peripheral nerve of the upper limb. In this article, we shall look at the applied anatomy of the nerve – its anatomical course, motor functions and cutaneous innervation. We shall also consider the clinical correlations of damage to the musculocutaneous nerve.

Nerve roots: C5-C6.

Motor functions: Innervates the muscles in the anterior compartment of the arm – the coracobrachialis, biceps brachii and the brachialis

Sensory functions: Gives rise to the lateral cutaneous nerve of forearm, which innervates skin on the lateral surface of the forearm.


Fig 1.0 - The anatomical course of the musculocutaneous nerve.

Fig 1.0 – The anatomical course of the musculocutaneous nerve.

Anatomical Course

The musculocutaneous nerve arises from the lateral cord of the brachial plexus, and therefore contains fibres from spinal roots C5, C6 and C7.

After originating from the brachial plexus, the musculocutaneous nerve leaves the axilla, and pierces the coracobrachialis muscle, near its point of insertion on the humerus.

It then passes down the arm, anterior to the brachialis muscle but deep 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. It provides sensory innervation to the lateral aspect of the forearm

NB: The musculocutaneous nerve is well recognised to have a varied anatomical course. It can interact with the median nerve, adhering to the nerve and exchanging fibres. 


Motor Functions

The musculocutaneous nerve innervates the muscles in the anterior compartment of the arm – the biceps brachii, brachialis and coracobrachialis. These muscles flex the upper arm at the shoulder and the elbow. In addition the biceps brachii also performs supination of the forearm.

A good memory tool to help you remember these muscles is BBC.


Fig 1.1 - Cutaneous distribution of the musculocutaneous nerve.

Fig 1.1 – Cutaneous distribution of the musculocutaneous nerve.

Sensory Functions

The musculocutaneous nerve gives rise to the lateral cutaneous nerve of forearm.

This nerve initially enters the deep forearm, but then pierces the deep fascia to become subcutaneous. In this region, it can be found in close proximity to the cephalic vein.

The lateral cutaneous nerve of forearm innervates the skin of the lateral aspect of the forearm.

 

Clinical Relevance: Lesions of the Musculocutaneous Nerve

How it commonly occurs: An injury to the musculocutaneous nerve is relatively uncommon, as it is well protected within the axilla. The most common cause is a stab wound to the axilla region.

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.

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