Musculocutaneous Nerve

Question 1

What is the musculocutaneous nerve?

Answer 1

A major peripheral nerve in the upper limb

Question 2

What are the nerve roots of the musculocutaneous nerve?

Answer 2

C5-C6

Question 3

What muscles does themusculocutaneous nerve innervate?

Answer 3

Muscles in the anterior compartment of the arm- the coracobrachialis, biceps brachii, and brachialis

Question 4

What is the sensory function of themusculocutaneous nerve?

Answer 4

Gives rise to the lateral cutaneous nerve of the forearm, which innervates skin on the lateral surface of the forearm

Question 5

What does themusculocutaneous nerve arise from?

Answer 5

The lateral cord of the brachial plexus, so contains fibres from spinal roots C5-7

Question 6

What course does themusculocutaneous nerve run?

Answer 6

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

Question 7

How does themusculocutaneous nerve continue in the forearm after emerging lateral to the biceps tendon?

Answer 7

As the lateral cutaneous nerve

Question 8

What does the lateral cutaneous nerve do?

Answer 8

Provides sensory innervation to the lateral aspect of the forearm

Question 9

What do the muscles innervated by the musculocutaneous nerve do?

Answer 9

Flex the upper arm at the shoulder and the elbow

The biceps brachii performs supination of the forearm

Question 10

What does themusculocutaneous nerve give rise to?

Answer 10

The lateral cutaneous nerve of forearm

Question 11

What course does the lateral cutaneous nerve of the forearm take?

Answer 11

Initially enters the deep forearm, but then pierces the deep fascia to become subcutaneous

Question 12

Where can the lateral cutaneous nerve of the forearm be found when its subcutaneous?

Answer 12

In close proximity to the cephalic vein

Question 13

Where does the lateral cutaneous nerve of the forearm innervate?

Answer 13

The skin of the lateral aspect of the forearm

Question 14

How common is injury to the musculocutaneous nerve?

Answer 14

Relatively uncommon

Question 15

Why is an injury to themusculocutaneous nerve relatively uncommon?

Answer 15

It is well protected within the axilla

Question 16

What is the most common cause of lesions of themusculocutaneous nerve?

Answer 16

A stab wound to the axilla region

Question 17

How are motor functions affected by lesions of themusculocutaneous nerve?

Answer 17

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

Question 18

Why can flexion at the shoulder still occur after injury to themusculocutaneous nerve?

Answer 18

Due to the pectoralis major

Question 19

Why can flexion at the elbow still occur after injury to themusculocutaneous nerve?

Answer 19

Because of the brachioradialis muscle

Question 20

Why can supination of the affected limb still be produced after injury to themusculocutaneous nerve?

Answer 20

Because it’s produced by the supinator muscle

Question 21

How does an injury to the musculocutaneous nerve affect sensory function?

Answer 21

Loss of sensation over the lateral side of the forearm