Terminal Nerves of the Brachial Plexus — Overview
The five major terminal nerves of the brachial plexus arise from the cords in the axilla and supply the entire upper limb. Each is a mixed nerve (motor + sensory + autonomic).
1. Axillary Nerve (C5, C6)
Origin: Posterior cord of brachial plexus
Course:
- Arises in the axilla; passes through the quadrangular space (bounded by: teres minor above, teres major below, long head of triceps medially, surgical neck of humerus laterally)
- Winds around the surgical neck of the humerus with the posterior circumflex humeral artery
- Divides into anterior and posterior branches deep to the deltoid
Branches:
- Motor to deltoid (anterior branch)
- Motor to teres minor (posterior branch) — carries a pseudoganglion
- Upper lateral cutaneous nerve of the arm — sensory to skin over lower half of deltoid (the “regimental badge” area)
- Articular branches to shoulder joint
Injury site: Fracture of surgical neck of humerus; shoulder dislocation; improper deltoid injection (upper deltoid)
Effects of injury:
- Paralysis of deltoid → loss of abduction (15°–90°) → arm cannot be abducted
- Flattening of the shoulder (rounded deltoid contour lost)
- Sensory loss over the regimental badge area (lower lateral deltoid)
2. Musculocutaneous Nerve (C5, C6, C7)
Origin: Lateral cord of brachial plexus
Course:
- Pierces coracobrachialis muscle (which it supplies)
- Runs between biceps brachii and brachialis in the arm (supplies both)
- Emerges lateral to the biceps tendon at the elbow
- Continues as the lateral cutaneous nerve of the forearm
Motor supply:
- Coracobrachialis
- Biceps brachii (flexion and supination of forearm)
- Brachialis (flexion of forearm)
Sensory supply:
- Lateral cutaneous nerve of the forearm → lateral aspect of the forearm
Effects of injury: Loss of flexion and supination of forearm; loss of biceps reflex
3. Radial Nerve (C5, C6, C7, C8, T1)
Origin: Posterior cord of brachial plexus; largest nerve of the brachial plexus
Course:
| Segment | Path | Branches Given |
|---|---|---|
| Axilla | Posterior to 3rd part of axillary artery, anterior to posterior axillary wall | Posterior cutaneous nerve of arm; nerve to long head + medial head of triceps |
| Arm | Passes between long and medial heads of triceps → spiral (radial) groove of humerus with profunda brachii artery | Lateral head of triceps; lower lateral cutaneous nerve of arm; posterior cutaneous nerve of forearm; anconeus |
| Anterior compartment of arm | Pierces lateral intermuscular septum; between brachioradialis and brachialis | Brachioradialis; ECRL; small part of brachialis |
| Cubital fossa | Divides into superficial (sensory) and deep (motor) branches at level of lateral epicondyle | — |
| Deep branch (posterior interosseous nerve) | Passes through supinator → posterior compartment of forearm | All extensor muscles of forearm; ECRB, supinator |
| Superficial branch | Deep to brachioradialis → emerges at wrist | Dorsum of hand (lateral 2/3) and dorsal surface of lateral 3½ digits (excluding nail beds) |
Motor supply summary:
- All muscles on the back of arm (triceps, anconeus)
- Brachioradialis and ECRL in the forearm (anterior compartment)
- All muscles on the back of forearm (extensors)
Sensory supply summary:
- Posterior arm and forearm
- Dorsal aspect of lateral 2/3 of hand; dorsal lateral 3½ digits (excluding nail beds)
Autonomous sensory area: First web space on dorsum of hand
4. Median Nerve (C5, C6, C7, C8, T1)
Origin: Two roots — lateral root from lateral cord (C5,6,7) + medial root from medial cord (C8,T1); roots unite in front of the axillary artery (Y-shaped junction)
Synonyms: “Laborer’s nerve” (hands-on work); nerve of the thenar eminence
Course:
| Segment | Key Points |
|---|---|
| Axilla | Lateral to axillary artery (3rd part) |
| Arm | No branches in arm; crosses brachial artery from lateral to medial at midhumerus |
| Cubital fossa | Medial to brachial artery; gives branches to all superficial flexors (except FCU) |
| Forearm | Passes between heads of pronator teres; gives anterior interosseous nerve (motor to FPL, lat ½ FDP, pronator quadratus) |
| Carpal tunnel | Deep to flexor retinaculum; gives off palmar cutaneous branch beforehand (over thenar eminence) |
| Palm | Divides → recurrent (thenar) branch + palmar digital branches |
Motor supply summary:
- Forearm: All superficial flexors except FCU (flexor carpi radialis, palmaris longus, FDS) + FPL, lat ½ FDP, pronator quadratus (via anterior interosseous nerve)
- Hand: Thenar muscles (APB, OP, FPB short head) + 1st and 2nd lumbricals
- Memory (LOAF): Lumbricals (1st and 2nd), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head)
Sensory supply:
- Palmar aspect of lateral 2/3 of hand and lateral 3½ digits (including nail beds)
- Palmar cutaneous branch → skin over thenar eminence (passes superficial to flexor retinaculum — spared in carpal tunnel syndrome)
Autonomous sensory area: Pulp of index finger
5. Ulnar Nerve (C7, C8, T1)
Origin: Medial cord of brachial plexus
Synonyms: “Musician’s nerve” (intrinsic hand muscles for fine finger movements)
Course:
| Segment | Key Points |
|---|---|
| Axilla | Between axillary artery and vein |
| Arm | No branches; runs medial to brachial artery → pierces medial intermuscular septum at midhumerus → posterior compartment → back of medial epicondyle |
| Medial epicondyle groove | Cubital tunnel — covered by fibrous band between medial epicondyle and olecranon; palpable here (“funny bone”) |
| Forearm | Between heads of FCU; gives branches to FCU and medial ½ FDP; gives palmar and dorsal cutaneous branches |
| Wrist (Guyon’s canal) | Lateral to pisiform; divides into superficial (sensory) and deep (motor) terminal branches |
Motor supply:
- Forearm: FCU (flexor carpi ulnaris) + medial ½ FDP = “1½ muscles”
- Hand: All intrinsic muscles except LOAF (the median nerve muscles): hypothenar muscles, 3rd + 4th lumbricals, all interossei (4 dorsal + 3 palmar), adductor pollicis, deep head of FPB
Sensory supply:
- Palmar aspect of medial 1/3 of hand and medial 1½ fingers
- Dorsal aspect of medial 1/3 of hand and medial 1½ fingers (via dorsal cutaneous branch)
Autonomous sensory area: Pulp of little finger
Comparison Table — Three Major Nerves of the Hand
| Feature | Radial Nerve | Median Nerve | Ulnar Nerve |
|---|---|---|---|
| Origin | Posterior cord | Lateral + medial cords | Medial cord |
| Root value | C5–T1 | C5–T1 | C7, C8, T1 |
| Motor — forearm | All extensors | Most flexors (except FCU + med ½ FDP) | FCU + med ½ FDP |
| Motor — hand | None (no intrinsics) | LOAF muscles | All intrinsics except LOAF |
| Sensory — hand | Dorsal lat 2/3 | Palmar lat 2/3 + lat 3½ digits | Palmar and dorsal med 1/3 + med 1½ fingers |
| Autonomous area | 1st web space dorsum | Pulp of index finger | Pulp of little finger |
| Synonym | — | Laborer’s nerve | Musician’s nerve |
| Injury deformity | Wrist drop | Ape thumb / Benediction hand | Ulnar claw hand |
Viva Pearls
- Radial nerve = largest nerve of brachial plexus; only nerve supplying all muscles of the back of arm and forearm
- Median nerve = only nerve formed from two cords (lateral + medial)
- No branches of median or ulnar nerve in the arm — clinically important
- Ulnar nerve has no branches in the axilla or arm; gives branches only in the forearm and hand
- LOAF = median nerve hand muscles (Lumbricals 1+2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis)
- Ulnar supplies “all intrinsics except LOAF”
- Palmar cutaneous branch of median = passes superficial to flexor retinaculum → thenar eminence spared in carpal tunnel syndrome
- Axillary nerve winds around surgical neck (not anatomical neck) of humerus
- Musculocutaneous nerve pierces coracobrachialis