Musculocutaneous Nerve Flashcards
What is the musculocutaneous nerve?
A major peripheral nerve in the upper limb
What are the nerve roots of the musculocutaneous nerve?
C5-C6
What muscles does themusculocutaneous nerve innervate?
Muscles in the anterior compartment of the arm- the coracobrachialis, biceps brachii, and brachialis
What is the sensory function of themusculocutaneous nerve?
Gives rise to the lateral cutaneous nerve of the forearm, which innervates skin on the lateral surface of the forearm
What does themusculocutaneous nerve arise from?
The lateral cord of the brachial plexus, so contains fibres from spinal roots C5-7
What course does themusculocutaneous nerve run?
After originating from the brachial plexus, it leaves the axilla and pierces the coracobrachialis muscle near its point of insertion at the humerus. It then passes down the arm, anterior to the brachialis muscle but deep to the biceps brachii, innervating them both. Themusculocutaneous nerve then emerges laterally to biceps tendon
How does themusculocutaneous nerve continue in the forearm after emerging lateral to the biceps tendon?
As the lateral cutaneous nerve
What does the lateral cutaneous nerve do?
Provides sensory innervation to the lateral aspect of the forearm
What do the muscles innervated by the musculocutaneous nerve do?
Flex the upper arm at the shoulder and the elbow
The biceps brachii performs supination of the forearm
What does themusculocutaneous nerve give rise to?
The lateral cutaneous nerve of forearm
What course does the lateral cutaneous nerve of the forearm take?
Initially enters the deep forearm, but then pierces the deep fascia to become subcutaneous
Where can the lateral cutaneous nerve of the forearm be found when its subcutaneous?
In close proximity to the cephalic vein
Where does the lateral cutaneous nerve of the forearm innervate?
The skin of the lateral aspect of the forearm
How common is injury to the musculocutaneous nerve?
Relatively uncommon
Why is an injury to themusculocutaneous nerve relatively uncommon?
It is well protected within the axilla
What is the most common cause of lesions of themusculocutaneous nerve?
A stab wound to the axilla region
How are motor functions affected by lesions of themusculocutaneous nerve?
The coracobrachialis, biceps brachii and brachialis muscles are paralysed. Flexion at the shoulder is weakened, but can still occur. Flexion at the elbow is also affected, but can still occur. Supination of the limb is greatly weakened
Why can flexion at the shoulder still occur after injury to themusculocutaneous nerve?
Due to the pectoralis major
Why can flexion at the elbow still occur after injury to themusculocutaneous nerve?
Because of the brachioradialis muscle
Why can supination of the affected limb still be produced after injury to themusculocutaneous nerve?
Because it’s produced by the supinator muscle
How does an injury to the musculocutaneous nerve affect sensory function?
Loss of sensation over the lateral side of the forearm
