Brachial plexus

Question 1

What can cause the nerves of the brachial plexus to get trapped?

Answer 1

1. Enlarged scalene muscles can compress nerves

2. Additional cervical rib can cause thoracic outlet syndrome

Question 2

What is the path of the brachial plexus to the upper limb?

Answer 2

1. Originates at the cervical vertebrae
2. Emerges between the anterior scalene and medial scalene muscles and runs through the posterior triangle of the neck
3. Passes behind the clavicle at approx. the midpoint [where it runs alongside the axillary artery to the upper limb]

Question 3

What makes up the posterior triangle of the neck?

Answer 3

Anterior = posterior border of sternocleidomastoid muscle
Posterior = anterior border of the trapezius muscle
Inferior = middle 1/3 of the clavicle

Question 4

Which spinal roots form the brachial plexus?

Answer 4

Ventral rami of C5-T1

Question 5

Which spinal roots form each trunk of the brachial plexus?

Answer 5

Upper trunk = C5 + C6
Middle trunk = C7
Lower trunk = C8 + T1

Question 6

Which divisions of each trunk form the cords of the brachial plexus?

Answer 6

Anterior divisions of the upper and middle trunks form the lateral cord
Posterior divisions of the upper, middle and lower trunks form the posterior cord
Anterior division of the lower trunk forms the medial cord

Question 7

What are the cords of the brachial plexus named in relation to?

Answer 7

Anatomical position in relation to the axillary artery

Question 8

What terminal branches of the brachial plexus does the lateral cord contribute to?

Answer 8

Musculocutaneous

Median

Question 9

What terminal branches of the brachial plexus does the posterior cord contribute to?

Answer 9

Radial

Axillary

Question 10

What terminal branches of the brachial plexus does the medial cord contribute to?

Answer 10

Median

Ulnar

Question 11

What muscles does the musculocutaneous nerve innervate?

Answer 11

Anterior arm compartment muscles (long and short head of the biceps brachii and the coracobrachialis)

Question 12

What are the functions of the biceps brachii?

Answer 12

Supination of forearm
Arm flexion at shoulder
Elbow flexion

Question 13

What are the functions of the coracobrachialis?

Answer 13

Arm flexion at shoulder

Weak adduction

Question 14

What would loss of innervation from the musculocutaneous nerve cause?

Answer 14

Loss of anterior compartment muscles (biceps brachii and coracobrachialis) leading to weakness of flexion of shoulder and elbow and weakness of supination of forearm

[Nb. uncommon to damage this nerve as is protected by muscles]

Question 15

What muscles does the axillary nerve innervate?

Answer 15

Deltoid

Teres minor

Question 16

What can damage the axillary nerve?

Answer 16

Shoulder dislocation

Fracture of the surgical neck of humerus

Question 17

What would loss of innervation from the axillary nerve cause?

Answer 17

Loss of innervation to the deltoids would cause loss of ability to abduct the arm and weakness in flexing and extending the arm at the shoulder
Loss of innervation to the teres minor would cause weakness in lateral rotation of the arm at the shoulder

Question 18

What does the median nerve innervate?

Answer 18

Anterior compartment of the forearm (except the flexor carpi ulnaris), thenar muscles (base of thumb) and lumbricals 1 + 2 (index and middle finger)

Question 19

How can the median nerve be damaged?

Answer 19

Penetrating injury to medial arm, laceration to anterior wrist or carpel tunnel

Question 20

What muscles does the radial nerve innervate?

Answer 20

Posterior arm compartment (three heads of the triceps brachii) and the posterior forearm compartment

Question 21

How can the radial nerve be damaged?

Answer 21

Fracture of humeral shaft (through spiral groove)

Dislocated or fractured head of radius (can affect the posterior interosseous nerve)

Question 22

What muscles does the ulnar nerve innervate?

Answer 22

Majority of the intrinsic muscles of hand

Question 23

How can the ulnar nerve be damaged?

Answer 23

Fracture of the medial humeral epicondyle

Injury to anterior wrist

Question 24

How can the C5 root and the upper trunk be damaged?

Answer 24

Penetrating neck injury

Question 25

What nerve roots does the radial nerve carry?

Answer 25

C5-T1

Question 26

What nerve root of the brachial plexus is vulnerable to damage from a Pancoast (apical lung) tumour and what can this result in?

Answer 26

T1 nerve root | Damage can cause wasting of the small muscles of the hand

Question 27

What muscle does the lateral pectoral nerve innervate?

Answer 27

Clavicular head of pectoralis major

Question 28

What muscles does the suprascapular nerve innervate?

Answer 28

Supraspinatus and infraspinatus rotator cuff muscles

Question 29

What muscles does the dorsal scapula nerve innervate?

Answer 29

Rhomboids | Levator scapulae

Question 30

What does damage to the suprascapular nerve result in?

Answer 30

Limits lateral rotation of shoulder and shoulder stability

Question 31

How can you identify damage to the long thoracic nerve?

Answer 31

Winging of the scapula (due to damage to the serratus anterior muscle)

Question 32

What can cause damage to the long thoracic nerve?

Answer 32

Axillary region surgery Incorrect thoracostomy Thoracotomy incision

Question 33

What muscles does the medial pectoral nerve innervate?

Answer 33

Sternal head of pectoralis major | Pectoralis minor

Question 34

How can damage to the brachial plexus be identified?

Answer 34

Abnormal resting position of the limb (due to loss of functionality in some muscles, remaining functional muscles pull limb into different position)

Question 35

What is Erb's Palsy and how can it be caused?

Answer 35

Damage to the C5 + C6 upper root/ trunk damage Caused by: Forced separation of the neck from the shoulder (e.g. through trauma such as cycling accident or during childbirth) causing stretching of nerves or evulsion of nerves from spinal cord Stab wound or laceration to the neck

Question 36

What resting limb position does an Erb's Palsy cause?

Answer 36

'Waiters tip' - limb is medially rotated, forearm pronated and hangs limp. Wasting of deltoid muscle.

Question 37

What is Klumpke's Palsy and how can it be caused?

Answer 37

``` Damage to the C8 + T1 root damage or compression Caused by: Upward traction of upper limb Apical lung tumour Compression via cervical rib ```

Question 38

What does a Klumpke's Palsy result in?

Answer 38

'Claw hand deformity' - extension of metacarpophalangeal joints and flexion of interphalangeal joints at rest Can also cause wasting of small muscles of hand