Peripheral nerves carry motor commands to muscles, sensory information to the central nervous system and autonomic fibres to vessels and glands. This page focuses on the spinal accessory, phrenic, radial, ulnar, median, musculocutaneous and axillary nerves requested in the curriculum. For each nerve, learn its roots, course, motor supply, sensory territory, key examination and common clinical problems.
Add your labelled peripheral-nerve image here.
Peripheral nerve, root and plexus are not the same
A spinal root carries fibres from one spinal level; a plexus mixes several roots; a peripheral nerve carries a new combination to muscles and skin. A C6 root lesion, median nerve lesion and lateral-cord lesion can therefore overlap but are not identical. Test more than one muscle and one sensory point, compare sides and consider the whole pattern.
Learning outcomes
- Trace the course and root values of the major upper-limb nerves.
- Identify the motor, sensory and important autonomic functions of each nerve.
- Perform a safe, structured motor, sensory, reflex and functional screen.
- Recognise common entrapment sites, injury mechanisms and urgent referral findings.
- Relate nerve deficits to physiotherapy treatment, splinting, exercise and ADLs.
1. General peripheral-nerve assessment
- History: mechanism, onset, pain quality, numbness, weakness, night symptoms, work/repetitive loading, surgery and systemic disease.
- Inspection: posture, muscle wasting, fasciculations, scapular position, hand posture, colour, swelling and skin injury.
- Motor screen: test movements supplied by different nerves and roots; observe range, force, timing and fatigue.
- Sensory screen: light touch, pinprick, vibration or proprioception according to training; compare named-nerve and dermatome patterns.
- Reflexes: biceps (C5–6, musculocutaneous), brachioradialis (C6, radial) and triceps (C7–8, radial) where appropriate.
- Neurodynamic/entrapment tests: only when trained, indicated and safe; do not provoke severe symptoms.
- Function and safety: grip, reach, dressing, transfers, protective sensation, skin care and work demands.
2. Spinal accessory nerve (cranial nerve XI)
The spinal accessory nerve has a cranial component that joins the vagus and a spinal component arising from upper cervical spinal cord segments. The spinal part exits the skull through the jugular foramen, crosses the posterior triangle and supplies sternocleidomastoid and trapezius.
| Feature | Details |
|---|---|
| Motor supply | Sternocleidomastoid and trapezius. |
| Actions tested | Head rotation against resistance; shoulder elevation/shrug; scapular upward rotation and retraction. |
| Injury risks | Posterior-triangle surgery, lymph-node biopsy, penetrating trauma or traction. |
| Possible findings | Shoulder droop, weak shrug, difficulty elevating arm above shoulder, lateral scapular displacement and fatigue. |
| Physiotherapy priorities | Protect the shoulder, retrain scapular control, prevent secondary pain and refer for neurological/surgical review. |
3. Phrenic nerve
The phrenic nerve arises mainly from C4 with contributions from C3 and C5. It descends on the anterior scalene, enters the thorax and travels to the diaphragm. It provides the principal motor supply to the diaphragm and sensory fibres to central diaphragmatic pleura, fibrous pericardium and parts of the peritoneum.
- Motor: diaphragm contraction increases thoracic volume for inspiration.
- Sensory: irritation of diaphragmatic or pericardial structures can be referred to the shoulder region through C3–5.
- Injury/impairment: reduced hemidiaphragm movement, orthopnoea, paradoxical motion or ventilatory compromise.
- Physiotherapy: monitor respiratory rate, work of breathing, chest expansion and oxygenation; escalate new respiratory weakness urgently.
4. Musculocutaneous nerve
The musculocutaneous nerve arises from the lateral cord (C5–7), pierces coracobrachialis and travels between biceps and brachialis. It continues as the lateral cutaneous nerve of the forearm.
| Feature | Details |
|---|---|
| Motor | Coracobrachialis, biceps brachii and brachialis; therefore shoulder flexion assistance, elbow flexion and supination. |
| Sensory | Lateral/anterior forearm through the lateral cutaneous nerve. |
| Mechanisms | Shoulder trauma, penetrating injury, coracobrachialis compression or traction. |
| Examination | Resisted elbow flexion in supination, resisted supination and sensation on lateral forearm; compare biceps reflex. |
| Functional effect | Difficulty lifting, bringing objects to the mouth and turning a palm upward. |
5. Axillary nerve
The axillary nerve arises from the posterior cord (C5–6). It passes through the quadrangular space with the posterior circumflex humeral artery, winds around the surgical neck of the humerus and divides into anterior and posterior branches.
| Feature | Details |
|---|---|
| Motor | Deltoid and teres minor; small branch to long head of triceps and shoulder joint. |
| Sensory | Superior lateral cutaneous nerve of arm—the “regimental badge” area over lower deltoid. |
| Injury mechanisms | Anterior shoulder dislocation, surgical-neck fracture, quadrangular-space compression or injection injury. |
| Findings | Weak abduction beyond initiation, flattened deltoid contour, weak external rotation and numbness over lateral shoulder. |
| Physiotherapy | Protect unstable/fractured shoulder, maintain safe range, monitor sensation and retrain deltoid only within medical restrictions. |
6. Radial nerve
The radial nerve is the major branch of the posterior cord (C5–T1). It passes posteriorly in the radial groove with the profunda brachii artery, crosses the lateral elbow and divides into superficial sensory and deep motor branches. The deep branch becomes the posterior interosseous nerve after passing through supinator.
| Region | Motor supply | Sensory supply | Clinical point |
|---|---|---|---|
| Arm | Triceps, anconeus, brachioradialis and wrist/finger extensors via branches. | Posterior arm/forearm branches. | Midshaft humeral fracture may injure the nerve in the radial groove. |
| Deep branch/PIN | Supinator and most posterior forearm extensors. | No significant cutaneous supply. | Motor weakness may occur without numbness; finger extension is affected. |
| Superficial branch | No major motor supply. | Dorsolateral hand, often sparing fingertips. | Compression near the forearm can cause dorsal hand symptoms. |
Examination: elbow extension, wrist extension, finger/thumb extension, brachioradialis reflex and sensation in the first dorsal web space. Wrist drop suggests significant radial-nerve dysfunction but must be localised clinically.
7. Median nerve
The median nerve is formed by lateral and medial roots from the lateral and medial cords (C6–T1, with variable C5 contribution). It descends with the brachial artery, crosses the cubital fossa, enters the forearm between pronator teres heads, passes beneath the flexor retinaculum and divides in the hand.
| Region | Motor supply | Sensory supply | Important lesion sites |
|---|---|---|---|
| Forearm | Most flexor–pronator muscles; anterior interosseous branch supplies FPL, pronator quadratus and lateral FDP. | Usually no major forearm skin supply. | Pronator teres, forearm fracture or laceration. |
| Hand | Thenar muscles and first two lumbricals via recurrent branch/digital branches. | Lateral palm and palmar thumb, index, middle and radial half of ring finger; dorsal fingertips of same digits. | Carpal tunnel, recurrent-branch injury or compression. |
| Anterior interosseous nerve | Pinch muscles: FPL, pronator quadratus, lateral FDP. | Motor only. | Weak “OK” pinch with flattened thumb/index tip flexion. |
Examination: thumb opposition/abduction, index and middle finger flexion, pronation, wrist flexion with radial deviation, sensation at index fingertip and carpal-tunnel provocation only when trained.
8. Ulnar nerve
The ulnar nerve arises from the medial cord (C8–T1, sometimes C7). It descends medial to the brachial artery, passes behind the medial epicondyle, travels between the heads of flexor carpi ulnaris and enters the hand through Guyon’s canal.
| Feature | Details |
|---|---|
| Motor in forearm | Flexor carpi ulnaris and medial half of flexor digitorum profundus. |
| Motor in hand | Most intrinsic muscles: interossei, hypothenar group, adductor pollicis and medial two lumbricals. |
| Sensory | Little finger and ulnar half of ring finger on palmar and dorsal aspects, with variation at the wrist. |
| Entrapment sites | Behind medial epicondyle/cubital tunnel and Guyon’s canal at the wrist. |
| Findings | Weak finger abduction/adduction, reduced pinch, clawing of ring/little fingers in advanced lesions and sensory change. |
Examination: finger abduction/adduction, Froment-type pinch observation, FCU/wrist function and sensation over the little-finger side. Protect the medial elbow from prolonged pressure.
9. Comparing major nerve patterns
| Nerve | Movement screen | Sensory key point | Common functional loss |
|---|---|---|---|
| Musculocutaneous | Elbow flexion and supination. | Lateral forearm. | Lifting a cup or turning palm upward. |
| Axillary | Shoulder abduction/external rotation. | Regimental badge. | Overhead reach and shoulder stability. |
| Radial | Elbow/wrist/finger extension. | First dorsal web space. | Release, grasp–release and wrist positioning. |
| Median | Pronation, thumb opposition and precision pinch. | Index fingertip/lateral palmar hand. | Buttoning, writing and picking up small objects. |
| Ulnar | Finger abduction/adduction and strong pinch. | Little-finger pulp. | Key pinch, spreading fingers and grip shaping. |
10. Physiotherapy management principles
- Protect the nerve and associated tissues from compression, traction, burns and prolonged awkward posture.
- Maintain safe passive range and tendon glide while avoiding overstretching denervated or healing structures.
- Use splinting to prevent contracture and support function when prescribed by the rehabilitation team.
- Retrain sensation, visual compensation and skin inspection when protective sensation is reduced.
- Progress active movement, strengthening and functional practice according to reinnervation, pain, fatigue and medical advice.
- Educate about work modification, elbow/wrist positioning, pressure avoidance and when to seek help.
Urgent referral features
Rapidly progressive weakness, severe new sensory loss, vascular colour/temperature change, severe pain after trauma, respiratory compromise, suspected compartment syndrome, open injury or new bowel/bladder or spinal-cord signs require urgent clinical review.
11. Examination points and revision questions
High-yield points
- Spinal accessory supplies trapezius/SCM; phrenic supplies the diaphragm.
- Axillary nerve winds around the surgical neck; radial nerve lies in the radial groove.
- Median nerve supplies most forearm flexors and thenar function; ulnar nerve supplies most intrinsic hand muscles.
- Musculocutaneous supplies the anterior arm and continues as lateral cutaneous forearm nerve.
- A named-nerve deficit must be distinguished from a root or plexus pattern.
- Describe the course, motor and sensory functions of the radial nerve.
- Compare median and ulnar nerve motor supply in the forearm and hand.
- Explain how an axillary nerve lesion affects shoulder function.
- What findings suggest a musculocutaneous lesion?
- Why can phrenic nerve dysfunction present as an upper-limb/shoulder complaint?
- Design a safe peripheral-nerve screen for a patient after humeral fracture.
References for further study
- NCBI Bookshelf: Nerves of the shoulder and upper limb
- NCBI Bookshelf: Axillary nerve
- TeachMeAnatomy: Upper-limb nerves
- American Family Physician: Peripheral nerve entrapment and injury
- UAMS: Nerves of the upper limb table
Educational note: This page supports anatomy learning and does not replace neurological consultation, electrodiagnostic testing or emergency management.