Nerves of the upper limb

Question 1

What are the spinal roots for the Musculocutaneous nerve?

Answer 1

C5-C7

Question 2

What are the motor functions of the Musculocutaneous nerve?

Answer 2

Innervate muscles in the anterior compartment of the arm. (Coracobrachialis, Biceps Brachii and the Brachialis muscles)

Question 3

What are the sensory functions of the Musculocutaneous nerve?

Answer 3

Gives rise to the lateral cutaneous nerve of the forearm, which innervates the lateral aspect of the arm.

Question 4

What is the anatomical course of the Musculocutaneous nerve?

Answer 4

1. 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.
2. It leaves the axilla and pierces the coracobrachialis muscle near its point of insertion on the humerus. It gives a branch to this muscle.
3. The musculocutaneous nerve then passes down the flexor compartment of the upper arm, superficial to brachialis but deep to the biceps brachii muscle. It innervates both these muscles and gives articular branches to the humerus and the elbow.
4. The nerve then pierces the deep fascia lateral to biceps brachii to emerge lateral to the biceps tendon and brachioradialis.
5. It continues into the forearm as the lateral cutaneous nerve and provides sensory innervation to the lateral aspect of the forearm.

Question 5

What are the spinal roots for the Axillary nerve?

Answer 5

C5, C6

Question 6

What are the sensory functions of the Axillary nerve?

Answer 6

Gives rise to upper lateral cutaneous nerve of arm, which innervates the skin over the lower deltoid (‘regimental badge area’).

Question 7

What are the motor functions of the Axillary nerve?

Answer 7

Innervates Teres minor and Deltoid muscles.

Question 8

What is the anatomical course of the Axillary nerve?

Answer 8

1. The axillary nerve is formed within the axilla area of the upper limb. It is a direct continuation of the posterior cord from the brachial plexus – and therefore contains fibres from the C5 and C6 nerve roots.
2. In the axilla, the axillary nerve is located posterior to the axillary artery and anterior to the subscapularis muscle.
3. It exits the axilla at the inferior border of subscapularis via the quadrangular space.
4. The axillary nerve then passes medially to the surgical neck of the humerus, where it divides into three terminal branches:
5. Posterior terminal branch – provides motor innervation to the posterior aspect of the deltoid muscle and teres minor. It also innervates the skin over the inferior part of the deltoid as the upper lateral cutaneous nerve of the arm.
6. Anterior terminal branch – winds around the surgical neck of the humerus and provides motor innervation to the anterior aspect of the deltoid muscle. It terminates with cutaneous branches to the anterior and anterolateral shoulder.
7. Articular branch – supplies the glenohumeral joint

Question 9

What is the quadrangular space?

Answer 9

The quadrangular space is a gap in the muscles of the posterior scapular region. It is a pathway for neurovascular structures to move from the axilla anteriorly to the posterior shoulder and arm.

Question 10

What are the borders of the Quadrangular space?

Superior, inferior, lateral, medial, and anterior.

Answer 10

Superior – inferior aspect of teres minor
Inferior – superior aspect of teres major
Lateral – surgical neck of humerus.
Medial – long head of triceps brachii
Anterior – subscapularis

Question 11

What can injury to the axillary nerve lead to?

Answer 11

Erb’s Palsy;
Erb’s palsy is a condition resulting from damage to C5-C6 roots of the brachial plexus. The axillary nerve is affected, and the individual is usually unable to abduct or externally rotate the shoulder joint.
It commonly occurs where there is an excessive increase in the angle between the neck and shoulder, which stretches (or even tears) the nerve roots.

Question 12

What are the nerve roots of the Radial nerve?

Answer 12

C5-T1

Question 13

What are the sensory functions of the Radial nerve?

Answer 13

Innervates most of the skin of the posterior side of forearm, the dorsal surface of the lateral side of the palm, and dorsal surface of the lateral three and a half digits.

Question 14

What are the motor functions of the Radial nerve?

Answer 14

Innervates the triceps brachii and the extensor muscles in the forearm.

Question 15

What is the anatomical course of the Radial nerve?

Answer 15

1. The radial nerve is the terminal continuation of the posterior cord of the brachial plexus. It therefore contains fibres from nerve roots C5 – T1.
   The nerve arises in the axilla region, where it is situated posteriorly to the axillary artery.
2. It exits the axilla inferiorly (via the triangular interval), and supplies branches to the long and lateral heads of the triceps brachii.
3. The radial nerve then descends down the arm, travelling in a shallow depression within the surface of the humerus, known as the radial groove.
4. As it descends, the radial nerve wraps around the humerus laterally, and supplies a branch to the medial head of the triceps brachii. During much of its course within the arm, it is accompanied by the deep branch of the brachial artery.
5. To enter the forearm, the radial nerve travels anterior to the lateral epicondyle of the humerus, through the cubital fossa. The nerve then terminates by dividing into two branches:
6. Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm.
   Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers.

Question 16

What are the nerve roots of the Median nerve?

Answer 16

C6-T1

Question 17

What are the sensory functions of the Median nerve?

Answer 17

Gives rise to the palmar cutaneous branch, which innervates the lateral aspect of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand.

Question 18

What are the motor functions of the Median nerve?

Answer 18

Innervates the flexor and pronator muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and part of the flexor digitorum profundus, innervated by the ulnar nerve). Also supplies innervation to the thenar muscles and lateral two lumbricals in the hand.

Question 19

What is the anatomical course of the Median nerve?

Answer 19

1. The median nerve is derived from the medial and lateral cords of the brachial plexus. It contains fibres from roots C6-T1, and can contain fibres from C5 in some individuals.
2. After originating from the brachial plexus in the axilla, the median nerve descends down the arm, initially lateral to the brachial artery.
3. Halfway down the arm, the nerve crosses over the brachial artery, and becomes situated medially. The median nerve enters the anterior compartment of the forearm via the cubital fossa.
4. In the forearm, the nerve travels between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives off two major branches in the forearm:
5. Anterior interosseous nerve – supplies the deep muscles in the anterior forearm.
   Palmar cutaneous nerve – innervates the skin of the lateral palm.
6. After giving off the anterior interosseous and palmar cutaneous branches, the median nerve enters the hand via the carpal tunnel – where it terminates by dividing into two branches:
7. Recurrent branch – innervates the thenar muscles.
   Palmar digital branch – innervates the palmar surface and fingertips of the lateral three and half digits. Also innervates the lateral two lumbrical muscles.

Question 20

What can compression of the Median nerve in the carpal tunnel lead to?

Answer 20

Carpal tunnel syndrome

Question 21

What is Carpal tunnel syndrome?

Answer 21

It is the most common mononeuropathy, and is caused by an increased tissue pressure within the carpal tunnel. Whilst risk factors for CTS have been identified (such as diabetes, pregnancy and acromegaly), the exact underlying aetiology is not well understood.
Clinical features include numbness, tingling, and pain in the distribution of the median nerve. Importantly, the palm is usually spared – as the palmar cutaneous branch does not travel through the carpal tunnel. Symptoms can wake the patient from sleep, and are usually worse in the morning. If left untreated, chronic CTS can cause weakness and atrophy of the thenar muscles.

Question 22

What are spinal roots of the Ulnar nerve?

Answer 22

C8-T1

Question 23

What are the sensory functions of the Ulnar nerve?

Answer 23

Innervates the anterior and posterior surfaces of the medial one and half fingers, and the associated palm area.

Question 24

What are the motor functions of the Ulnar nerve?

Answer 24

Innervates the intrinsic muscles of the hand (apart from the thenar muscles and two lateral lumbricals), and two muscles in the forearm; flexor carpi ulnaris and medial half of flexor digitorum profundus.

Question 25

What is the anatomical course of the Ulnar nerve?

Answer 25

1. The ulnar nerve arises from the brachial plexus. It is a continuation of the medial cord, containing fibres from spinal roots C8 and T1.
2. After arising from the brachial plexus, the ulnar nerve descends down the medial aspect of the upper arm.
3. At the elbow, it passes posterior to the medial epicondyle of the humerus and gives rise to an articular branch that supplies the elbow joint. The ulnar nerve is palpable and vulnerable to injury at the medial epicondyle.
4. In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris, and travels deep to the muscle, alongside the ulna. Three main branches arise in the forearm:
5. Muscular branch – innervates two muscles in the anterior compartment of the forearm.
   Palmar cutaneous branch – innervates the medial half of the palm.
   Dorsal cutaneous branch – innervates the dorsal surface of the medial one and a half fingers, and the associated dorsal hand area.
6. At the wrist, the ulnar nerve travels superficially to the flexor retinaculum, and is medial to the ulnar artery. It enters the hand via the ulnar canal (Guyon’s canal). In the hand, the nerve terminates by giving rise to superficial and deep branches.