Nerves - Musculocutaneous Flashcards
What are the nerve roots of the musculocutaneous nerve?
C5-C7
Sensory function?
The musculocutaneous nerve gives rise to the lateral cutaneous nerve of the forearm.
The nerve initially enters the deep forearm, but then pierces the deep fascia to become subcutaneous. In this region, it can be found close to the cephalic vein.
The lateral cutaneous nerve of forearm innervates the skin of the anterolateral aspect of the forearm.
Motor function?
The musculocutaneous nerve innervates the muscles in the anterior compartment of the forearm:
- Biceps brachii
- Brachialis
- Coracobrachialis
These muscles flex the upper arm at the shoulder and the elbow. In addition, the biceps brachii also supinates the forearm.
A useful mnemonic is BBC.
Anatomical course?
The musculocutaneous nerve is the terminal branch of the lateral cord of the brachial plexus (C5, C6 and C7) and emerges at the inferior border of pectoralis minor muscle.
It leaves the axilla and pierces the coracobrachialis muscle near its point of insertion on the humerus. It gives a branch to this muscle. The nerve then passes down the flexor compartment of the upper arm, superficial to brachialis by deep to the biceps brachii muscle. It innervates both these muscles and gives articular branches to the humerus and the elbow.
The nerve then pierces the deep fascia lateral to biceps brachii to emerge lateral to the biceps tendon and brachioradialis. It continues into the forearm as the lateral cutaneous nerve and provides sensory innervation to the lateral aspect of the forearm.
Although it has a varied course.
Clinical relevance: injury to the musculocutaneous nerve
The musculocutaneous nerve is well protected within the axilla and injury is relatively uncommon. Characteristic mechanisms of injury include penetrating trauma to the axilla (e.g stabbing). and iatrogenic injury resulting from heavy retraction during the deltopectoral approach to the shoulder.
