Brachial plexus, nerves and vessels of the upper limb

Question 1

Which spinal segments supply the upper limb and its limb girdle?

Answer 1

C4-T1 (sensory and motor)

Question 2

Which spinal segments supply muscles responsible for movements of the shoulder girdle?

Answer 2

C4 and C5

Question 3

Which spinal segments supply muscles responsible for movements of the shoulder joint?

Answer 3

C5 and C6

Question 4

Which spinal segments supply muscles responsible for movements of the elbow joint?

Answer 4

C6 and C7

Question 5

Which spinal segments supply muscles responsible for movements of the wrist joint?

Answer 5

C7 and C8

Question 6

Which spinal segments supply muscles responsible for movements of the fingers and thumb?

Answer 6

C8 and T1

Question 7

What is the function of the brachial plexus?

Answer 7

To rearrange the nerve fibres from C5-T1 into bundles travelling to appropriate parts of the limb.

Question 8

What do all nerves supplying extensor muscles of the upper limb pass through?

Answer 8

A bundle in the brachial plexus- the posterior cord.

Question 9

What do all nerves supplying flexor muscles of the upper limb pass through?

Answer 9

Bundles in the brachial plexus- lateral and medial cords.

Question 10

Which 2 nerves does the posterior cord of the brachial plexus divide into?

Answer 10

Axillary nerve Radial nerve

Question 11

What is the path and main function of the axillary nerve?

Answer 11

Winds around the neck of the humerus to supply C5 and C6 fibres to deltoid, the main abductor of the shoulder.

Question 12

What is the clinical significance of the axillary nerve?

Answer 12

It can be injured in shoulder dislocations and upper humeral fractures, resulting in loss of abduction and eventual wasting of the deltoid (all skeletal muscles eventually waste if deprived of their nerve supply and are therefore inactive).

Question 13

Describe the path of the radial nerve.

Answer 13

Winds posterior to the humerus in the radial (spiral) groove between the attachments of the medial and lateral heads of triceps.

Question 14

What is the clinical significance of the radial nerve?

Answer 14

Its C7-T1 fibres can be damaged by fractures of the mid-humeral shaft, leading to loss of function of the extensor muscles in the forearm. This causes wrist drop, and results in great weakness of the ‘power grip’. Sensory loss from this injury affects a variable area on the posterior surface of the thumb (because of substantial overlap with other nerves).

Question 15

What is the most important branch of the lateral cord of the brachial plexus?

Answer 15

Musculocutaneous nerve.

Question 16

What does the musculocutaneous nerve supply and what is its clinical significance?

Answer 16

Biceps and brachialis (elbow flexors). Biceps is the key muscle in supination. Well away from most dangers, but muscles are affected in upper brachial plexus nerve root injuries. Contains C5-C7 fibres.

Question 17

What is the main branch of the medial cord of the brachial plexus?

Answer 17

Ulnar nerve

Question 18

What is the clinical significance of the ulnar nerve?

Answer 18

Motor nerve of most of the intrinsic muscles of the hand. Most vulnerable to compression, cuts and fractures where it passes posterior to the medial epicondyle of the humerus at the elbow. This produces weakness and wasting of many small muscles of the hand, though this is less serious than might be expected- the really vital small muscles of the hand, controlling fine movements of the thumb and index finger, are served by the median nerve. Clawing of the fingers may be seen, produced by unopposed activity of the long muscles of the fingers lying in the forearm. Sensory loss in median nerve injury is along the medial part of the hand, and the medial (usually 1.5) fingers.

Question 19

What is the clinical significance of the median nerve?

Answer 19

Acquires C6-T1 fibres. Formed from lateral and medial cords of brachial plexus. Supplies most of the wrist and finger flexors in the forearm, and most of the small muscles of the thumb and index finger. Its sensory fibres supply the lateral part of the hand, so injury or entrapment makes delicate hand activities such as writing difficult or impossible. Well protected from extrinsic injury, but often becomes entrapped as it passes through the carpal tunnel between wrist and hand. Carpal tunnel syndrome is the commonest serious neurological problem of the upper limb; fortunately it usually responds well to surgical release of the trapped nerve.

Question 20

What are the dermatomes of the upper limb?

Answer 20

C4 shoulder

C5 lateral side of arm

C6 lateral side of forearm

C7 middle and ring finger

C8 medial side of hand, forearm and little finger

T1 medial side of upper forearm and arm

T2 axilla