The Brachial Plexus

Question 1

What is the brachial plexus?

Answer 1

• A network of nerve fibres (spinal nerves) that supplies the skin and musculature of the upper limb.
• It begins at the root of the neck.

Question 2

What are the roots of the brachial plexus?

Answer 2

• C5-T1: C5, C6, C7, C8 and T1
• The roots are known as the anterior rami of the spinal nerves that form the brachial plexus.
• They leave the spinal cord via the intervertebral foramina of the vertebral column. The nerves pass through the anterior and middle scalene.

Question 3

What are the trunks of the brachial plexus?

Answer 3

• The trunks are the convergence of the roots. There are superior, middle and inferior trunks.
• Superior: a combination of C5 and C6
• Middle: continuation of C7
• Inferior: a combination of C8 and T1

The trunks cross the posterior triangle of the neck (lateral aspect of the neck).

Question 4

What are the divisions of the brachial plexus?

Answer 4

• This is the division of each trunk into anterior and posterior divisions. This leads to 3 anterior nerve fibres and 3 posterior nerve fibres.
• They pass into the axilla.

Question 5

What are the cords of the brachial plexus?

Answer 5

• These are the combinations of the divisions. There are 3 cords: the lateral cord, the posterior cord and the middle cord.
• The lateral cord is formed by the anterior division of the superior trunk and the anterior division of the middle trunk
• The posterior cord is formed by the posterior division of the superior trunk, the posterior division of the middle trunk and the posterior trunk of the inferior trunk.
• The medial cord is formed by the anterior division of the inferior trunk.

Question 6

What are the branches of the brachial plexus?

Answer 6

MARMU (lateral to medial)

• Musculocutaneous nerve (C5-C7)
• Axillary nerve (C5-C6)
• Radial nerve (C5-T1)
• Median nerve (C6-T1) - sometimes also C5 in some individuals
• Ulnar nerve (C8-T1)

Question 7

What is the musculocutaneous nerve?

Answer 7

• C5-C7
• Lateral cord
• Provides motor innervation to the biceps brachii, brachialis, coracobrachialis. It flexes the upper arm at the elbow and shoulder; it also supinates the forearm (due to biceps).
• The lateral cutaneous branch provides sensory innervation to the lateral half of the anterior forearm and a small portion of the lateral side of the posterior forearm

Question 8

What is the axillary nerve?

Answer 8

• C5-C6
• There are 3 divisions of the axillary nerve: the posterior terminal branch, the anterior terminal branch and the articular branch.
• The posterior terminal branch provides motor innervation to the posterior deltoid and the teres minor. It innervates the inferior region of the deltoid as the upper lateral cutaneous nerve.
• The anterior terminal branch provides motor innervation to the anterior deltoid. It winds around the surgical neck of the humerus.
• The articular branch supplies the glenohumeral joint.

Question 9

What is the radial nerve?

Answer 9

• C5-T1
• The deep branch provides motor innervation to the triceps brachii which extends the elbow and also innervates the extensors of the wrist and fingers (e.g. brachioradialis and extensor carpi radialis) which extend and supinate.
• There are 4 branches for sensory innervation: lower lateral cutaneous nerve of arm, posterior cutaneous nerve of arm, posterior cutaneous nerve of forearm, and the superficial branch.
• The lower lateral cutaneous nerve of the arm innervates the lateral aspect of the arm, inferior to the insertion of the deltoid muscle.
• The posterior cutaneous nerve of the arm innervates the posterior surface of the arm
• The posterior cutaneous nerve of the forearm innervates a strip of skin down the middle of the posterior forearm.
• The superficial branch innervates the dorsal surface of the lateral three and a half digits and the associated area on the dorsum of the hand.

Question 10

What is the median nerve?

Answer 10

• C6-T1
• It travels between the flexor digitorum profundus and flexor digitorum superficialis muscles.
• The median nerve innervates the superficial and intermediate muscles of the forearm - pronator teres, flexor carpi radialis, palmaris longus and flexor digitorum superficialis.
• The anterior interosseous nerve (a branch of the median nerve) innervates the deep muscles of the forearm - flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus (the medial half of the muscle is innervated by the ulnar nerve).
• The recurrent branch of the median nerve innervates the thenar muscles – muscles associated with movements of the thumb.
• The palmar digital branch innervates the lateral two lumbricals and provides sensory innervation to the palmar surface and fingertips of the lateral three and a half digits.
• The palmar cutaneous branch innervates the lateral aspect of the palm.

Question 11

What is the ulnar nerve?

Answer 11

• C8-T1
• The muscular branch innervates the anterior compartment of the forearm - flexor carpi ulnaris, half of flexor digitorum profundus.
• The deep branch innervates the intrinsic muscles of the hand - the hypothenar muscles, medial two lumbricals, adductor pollicis, palmar and dorsal interossei of the hand, and palmaris brevis.
• The palmar cutaneous branch innervates the medial half of the palm
• The dorsal cutaneous branch innervates the dorsal surface of the medial 1.5 fingers and the associated dorsal region
• The superficial branch innervates the palmar surface of the medial 1.5 fingers.

Question 12

What are the 11 smaller nerves that arise from the brachial plexus?

Answer 12

• Dorsal scapular nerve
• Long thoracic nerve
• Suprascapular nerve
• Nerve to subclavius
• Lateral pectoral nerve
• Medial pectoral nerve
• Medial cutaneous nerve of arm
• Medial cutaneous of the forearm
• Superior subscapular nerve
• Thoracodorsal nerve
• Inferior subscapular nerve

Question 13

What is Erb’s palsy?

Answer 13

• Upper brachial plexus injury
• C5-C6 roots are affected so this includes the musculocutaneous, axillary, suprascapular, and nerve to subclavius.
• Muscles affected – supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid and teres minor.
• Motor functions affected – abduction at shoulder, lateral rotation of the arm, supination of the forearm, and flexion at the shoulder.
• Sensory functions affected – sensation over the lateral aspect of upper limb (C5-6 dermatomes).
• The affected limb hangs limply, medially rotated by the unopposed action of pectoralis major. The forearm is pronated due to the loss of biceps brachii. The wrist is weakly flexed due to the normal tone of the wrist flexors relative to the weakened wrist extensors. This is position is known as ‘waiter’s tip’ and is characteristic of Erb’s palsy.

Question 15

What is Klumpke’s palsy?

Answer 15

• Lower brachial plexus injury
• Nerves affected – the peripheral nerves derived from T1 root are most affected; the ulnar and median nerves
• Muscles affected – the intrinsic hand muscles
• Sensory functions affected – sensation along the medial side of upper limb (C8-T1 dermatomes).

The primary feature of Klumpke’s palsy is a clawed hand. This occurs due to paralysis of the lumbrical muscles, which normally act to flex the metacarpophalangeal joints (MCPJs) and extend the interphalangeal joints (IPJs). When paralysed, the fingers subsequently become extended at the MCPJs and flexed at the IPJs, producing a clawed appearance.