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The brachial plexus is the nerve plexus of the upper limb.  Below is a summary of the key points of the brachial plexus, however if you’d like to gain a deeper understanding head over to our comprehensive brachial plexus guide.

Highlighted in red are the 5 major terminal nerves of the plexus.

Advice

Don’t make it complicated.

This plexus is one of the easiest to learn, and we have focused on the clinical stuff, as that is ultimately what counts. 

You shouldn’t obsess with the details, focus on the basics (what region does the nerve supply).

You will remember the details with time and revision.

Structure of the brachial plexus

An easy way to remember the structure is:

Real Teens Drink Cold Beer

 

Roots

Trunks

Divisions

Cords

Branches

 

Roots

Anterior rami of spinal nerves C5-T1:

  • These exit the intervertebral foramina, and pass between scalenus anterior and scalenus medius.
  • The plexus then runs in the axilla.
  • Occasionally you get a prefixed (C4 included) or post fixed (T2 included) plexus.

 

C3-5

Only C5 forms part of the brachial plexus 

This root gives rise to the phrenic nerve (mainly C4).

The phrenic nerve supplies the diaphragm “C3/4/5 keeps the diaphragm alive”

 

C4-5

Give rise to the dorsal scapular nerve

The dorsal scapular nerve innervates the rhomboid muscles & levator scapulae

 

C5-7

Gives rise to the long thoracic nerve

This innervates serratus anterior (a scapular protractor)

 

Trunks

UPPER TRUNK –  formed by the merging of C5 and C6. Gives rise to:

  • (C5-6) The suprascapular nerve: This innervated the supraspinatus (shoulder abductor) and infraspinatus (external rotator of shoulder)
  • (C5-6) The nerve to subclavius

 

MIDDLE TRUNK  a continuation of C7

 

LOWER TRUNK – formed by the merging of C8 and T1

Divisions

Each trunk has a posterior and anterior division.

The posterior divisions of each trunk join to form the posterior cord.

 

Cords

These are named by their position relative to the axillary artery, which they surround.

 

MEDIAL CORD BRANCHES

C8-T1 – Medial pectoral nerve  supplies pec major and minor (mainly minor)

C8-T1 – Ulnar nerve:

  • Supplies flexor carpi ulnaris
  • Ulnar head of flexor digitorum profundus
  • All the interossei of the hand (4 dorsal and 3 palmar)
  • Adductor pollicis brevis
  • Sensory innervation is the ulnar 1 and a half fingers both palmarly and dorsally

 

C8-T1 – Medial root to the median nerve

C8-T1 – Medial cutaneous nerve of the forearm  supplies sensation to the medial surface of the forearm.

C8-T1 – Medial cutaneous nerve of the forearm  supplies sensation to the medial surface of the arm.

 

POSTERIOR CORD BRANCHES

C5-T1 – Radial nerve:

  • Supplies all the muscles on the back of the arm (triceps brachii, all the muscles of the forearms extensor compartment)
  • Brachioradialis is also supplies by the radial nerve, but acts as a forearm supinator and elbow flexor
  • Supplies sensation to the back of the arm (posterior cutaneous nerve of the arm)
  • Supplies sensation to the back of the hand (see below)
  • The nerve exits the axilla via the quadrangular space
  • It then runs in the spiral groove of the humerus with profunda brachii

 

(C5-6) Axillary nerve:

  • Supplies deltoid
  • Sensory innervation is the regimental patch area of the shoulder
  • The nerve exits the axilla via the triangular space

 

(C6-8) Thoracodorsal nerve  supplies latissimus dorsi

(C5-6) Upper subscapular nerve supplies subscapularis (medial rotator)

(C5-C6) Lower subscapular nerve supplies the subscapularis and teres major (shoulder adductor)

 

LATERAL CORD BRANCHES

(C5-7) Lateral pectoral nerve – supplies both pec major and minor, but mainly major.

(C5-7) Musculocutaneous nerve:

  • Supplies the flexor compartment of the arm (biceps brachii / coracobrachialis / brachialis)
  • First muscle it enters is coracobrachialis
  • Terminates as the lateral cutaneous nerve of the forearm

 

(C5-7) Lateral root to the median nerve:

  • Median nerve – formed by a branch from both the medial and lateral cord
  • Median nerve supplies all the flexors of the forearm (except the ulnar head of flexor digitorum profundus and flexor carpi ulnaris).
  • Median nerve also supplies the muscles of the thenar eminence of the hand (flexor pollicis brevis / abductor pollicis brevis / opponens pollicis).
  • Also supplies the radial two lumbricals.
  • It DOES NOT supply adductor pollicis brevis.
Brachial plexus

Brachial plexus

 

Clinical points

Erb’s palsy

Upper roots are damaged, usually C5-6. Patient has a ‘waiter’s tip’ position (elbow is extended, shoulder is internally rotated and forearm is pronated). This is because the axillary nerve, suprascapular nerve, and musculocutaneous nerve are affected.

 

Klumpke’s palsy

Lower roots are damaged, usually C8 and T1. Usually occurs during childbirth. Symptoms are similar to an ulnar palsy, but also causes loss of sensation to the medial surface of the arm and forearm, as well as weakness of pectoralis minor.

 

Ulnar paradox / Ulnar claw

Normally the more proximal the nerve injury, the worse the symptoms. Not with the ulnar nerve. A proximal injury denervates the finger flexors (ulnar head of FDP) as well as the intrinsic hand muscles. Hence the patient has an open palm. Distal injury leaves the FDP intact, resulting in a clawed appearance that is disabling.

 

Radial nerve (Saturday night) palsy

Compression of the axilla compresses the radial nerve. Symptoms are wrist drop and loss of sensation to the back of the arm.

 

Axillary nerve palsy

Usually caused by a downward dislocation of the shoulder. Results in loss of sensation over the regimental patch, and weakness of shoulder abduction (due to deltoid being denervated).

 

Winged scapula

Damage to the long thoracic nerve denervates the serratus anterior muscle. The scapula can no longer be protracted, and so appears winged.

 

Hand of benediction

This is caused by prolonged compression of the medial nerve at the elbow. This results in an inability to flex (due to denervation of the finger flexors of index and middle fingers) and extend the interphalangeal joints of index and middle finger (due to the radial two lumbricals being denervated).

When a patient tries to make a fist, the index and finger and middle finger cannot flex (due to denervation of the finger flexors), while the lateral two fingers can (ulnar head of FDP still innervated). This result in the classic ‘hand of benediction.’

 

Review questions

1) What are the nerve roots of the radial nerve?

2) What muscle does the musculocutaneous nerve supply first?

3) What are the two forearm muscles supplied by the ulnar nerve?

4) Which hand muscles does the medial nerve supply?

5) Damage to which nerve causes winged scapula?

 

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