Anatomy chapters
Nerves of the upper limb
Follow the major nerves from the axilla to the hand, and localise lesions using muscle weakness and sensory loss.
- Five terminal nerves connect plexus anatomy to examination.
- Median supplies most forearm flexors; ulnar supplies most intrinsic hand muscles.
- Lesion level is identified by spared movements and sensation.
On this page
Overview
The upper limb receives most of its motor and sensory nerves through the brachial plexus.
Its terminal nerves contain fibres from several spinal segments, so a peripheral nerve injury produces a different pattern from a single root lesion.
Learn each nerve as a journey: where it begins, which landmark it crosses, what it supplies and where it can be injured.
A movement plus a small patch of altered sensation often localises the lesion better than a named deformity alone.
Major nerves at a glance
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Musculocutaneous | Lateral cord, C5–C7 | Anterior arm; lateral forearm skin | Weak elbow flexion and supination |
| Axillary | Posterior cord, C5–C6 | Deltoid, teres minor; lower deltoid skin | At risk at the surgical neck |
| Radial | Posterior cord, C5–T1 | Posterior arm and forearm; posterior limb skin | A proximal lesion causes wrist drop |
| Median | Lateral and medial cords, C5–T1 | Most forearm flexors, thenar muscles and lateral two lumbricals | Compressed in the carpal tunnel |
| Ulnar | Medial cord, mainly C8–T1 | Flexor carpi ulnaris, medial FDP and most intrinsic hand muscles | Vulnerable behind the medial epicondyle |
Root values describe the usual contribution. They do not mean that every muscle supplied by the nerve uses every listed root.
Musculocutaneous and axillary nerves
The musculocutaneous nerve pierces coracobrachialis and runs between biceps and brachialis. Near the lateral side of the biceps tendon it becomes the lateral cutaneous nerve of the forearm.
It supplies all three anterior arm muscles; a small lateral part of brachialis also receives radial innervation.
Test elbow flexion with the forearm supinated. Brachioradialis can still flex the elbow after musculocutaneous injury, so flexion is weakened rather than necessarily abolished.
The axillary nerve passes backwards through the quadrangular space with the posterior circumflex humeral artery. Teres minor is above, teres major below, the long head of triceps medially and the surgical neck laterally.
The nerve winds around the surgical neck deep to deltoid.
Test deltoid by resisted abduction and compare sensation over its lower lateral surface. Teres minor assists lateral rotation, but infraspinatus can preserve some of this movement.
A typical radial-groove lesion causes wrist drop with preserved elbow extension.
Radial nerve
The radial nerve leaves the axilla through the triangular interval and accompanies the profunda brachii artery in the radial groove.
It pierces the lateral intermuscular septum, reaches the front of the lateral elbow and divides into superficial and deep branches.
Branches in the arm supply triceps, brachioradialis and extensor carpi radialis longus.
The deep branch supplies extensor carpi radialis brevis and supinator, then continues through supinator as the posterior interosseous nerve to the remaining extensor muscles.
The superficial branch is cutaneous. It descends beneath brachioradialis, then turns onto the dorsolateral wrist and hand. Test its relatively distinct territory in the dorsal first web space.
It does not supply the index fingertip.
A lesion in the axilla affects elbow, wrist and finger extension. A typical radial-groove lesion spares elbow extension because triceps branches have already left.
A posterior interosseous lesion mainly affects finger and thumb extension, without cutaneous sensory loss; wrist extension may persist with radial deviation.
The anterior interosseous nerve supplies FPL, pronator quadratus and lateral FDP.
Median nerve
The median nerve forms in front of the axillary artery. In the arm it starts lateral to the brachial artery and usually crosses anterior to it to reach the medial side. It gives no major muscular branches in the arm.
At the elbow it lies medial to the brachial artery, deep to the bicipital aponeurosis.
It passes between the heads of pronator teres and beneath the fibrous arch of flexor digitorum superficialis, then descends between superficialis and profundus.
The anterior interosseous branch runs on the interosseous membrane. It supplies flexor pollicis longus, pronator quadratus and the lateral part of flexor digitorum profundus. It has no cutaneous territory.
At the wrist the median nerve enters the carpal tunnel with nine flexor tendons. Its palmar cutaneous branch leaves proximal to the tunnel and passes superficial to the flexor retinaculum.
In the hand, recurrent and digital branches supply the thenar muscles and lateral two lumbricals.
Median sensation covers the palmar lateral three and a half digits and their distal dorsal surfaces. The thenar skin is supplied by the palmar cutaneous branch.
The deep ulnar branch supplies every interosseous muscle.
Ulnar nerve
The ulnar nerve descends medially in the arm, crosses the medial intermuscular septum and passes behind the medial epicondyle. It enters the forearm between the heads of flexor carpi ulnaris and runs on profundus.
In the distal forearm the ulnar artery lies lateral to it.
It enters the hand superficial to the flexor retinaculum through Guyon's canal, between the pisiform and hook of hamate. A superficial branch is mainly sensory; a deep branch supplies most intrinsic muscles.
These include the interossei, medial two lumbricals, hypothenar muscles, adductor pollicis and deep head of flexor pollicis brevis.
The dorsal cutaneous branch leaves in the forearm, so a canal lesion may spare dorsal ulnar hand sensation.
A pure interosseous nerve lesion causes weakness without a cutaneous sensory deficit.
Collateral branches
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Long thoracic | C5–C7 roots | Serratus anterior | Injury causes winging |
| Dorsal scapular | C5 root | Rhomboids; assists levator supply | Scapular retraction |
| Suprascapular | Upper trunk C5–C6 | Supraspinatus and infraspinatus | Weak abduction initiation and external rotation |
| Thoracodorsal | Posterior cord C6–C8 | Latissimus dorsi | At risk during axillary surgery |
| Subscapular nerves | Posterior cord C5–C6 | Subscapularis; lower branch also teres major | Medial rotation |
| Pectoral nerves | Lateral/medial cords C5–T1 collectively | Pectoral muscles | Supply overlaps in pectoralis major |
Other cutaneous nerves
The medial cutaneous nerves of the arm and forearm arise from the medial cord. The intercostobrachial nerve, usually from T2, supplies the axillary floor and adjoining medial upper arm.
Therefore, not all upper-limb skin is supplied by the brachial plexus.
Clinical relevance
Carpal tunnel syndrome
How it happens: Pressure rises around the median nerve beneath the flexor retinaculum.
What you see: Tingling affects the lateral three and a half digits; advanced compression weakens opposition and wastes the thenar muscles.
Thenar skin sensation is usually preserved because its palmar cutaneous branch bypasses the tunnel.
Anterior interosseous palsy
How it happens: The motor branch to flexor pollicis longus, pronator quadratus and lateral profundus is damaged.
What you see: The thumb–index pinch circle becomes flattened through weak thumb interphalangeal and index distal interphalangeal flexion. Skin sensation remains intact.
Ulnar palsy and Froment's sign
How it happens: Ulnar injury paralyses adductor pollicis and weakens interossei.
What you see: Paper pinch is weak; the patient bends the thumb tip using median-supplied flexor pollicis longus to compensate. Finger spreading and closing are also weak.
Ulnar claw and the ulnar paradox
How it happens: Loss of intrinsic muscle balance leaves the long extensors and flexors relatively unopposed.
What you see: Ring and little metacarpophalangeal joints hyperextend while their interphalangeal joints flex. Clawing can be greater in distal injury because the ulnar profundus remains active; a smaller claw does not establish a milder lesion.
Localise lesions using the muscles spared, not just the muscles lost. Distinguish carpal tunnel from a proximal median lesion, and posterior interosseous palsy from radial-groove injury. Use dorsal hand sensation to separate ulnar wrist lesions from more proximal lesions.
Quick revision
- Musculocutaneous pierces coracobrachialis and ends in lateral forearm skin.
- Axillary nerve crosses the quadrangular space and surgical neck.
- Radial nerve accompanies profunda brachii in the radial groove.
- Anterior and posterior interosseous lesions cause no cutaneous sensory deficit.
- Median palmar cutaneous fibres bypass the carpal tunnel.
- Ulnar nerve passes behind the medial epicondyle and through Guyon's canal; interossei are supplied by the deep ulnar branch.
Sources: Snell's Clinical Anatomy by Regions, supplied Upper Limb chapter; UHS PGET Paper I MBBS Table of Specifications. Supplementary clinical testing and developmental context follow standard examination conventions and Duke Embryology where relevant. Picture links are visual study resources. Text and tables written independently for The House Job.
FAQ
Which nerve supplies the first dorsal web space?
The superficial radial nerve. This is a useful site for testing radial cutaneous function.
Why is the palm often spared in carpal tunnel syndrome?
The palmar cutaneous branch travels superficial to the flexor retinaculum and avoids the tunnel.
Does a posterior interosseous lesion cause complete wrist drop?
Usually not. Extensor carpi radialis longus remains supplied, so wrist extension may remain, often with radial deviation.
Which nerve is tested by finger abduction?
The ulnar nerve, through the dorsal interossei. Test against resistance and compare both hands.