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Upper Limb Anatomy - MBBS 1st Year Notes
Source: Gray's Anatomy for Students
1. Overview
The upper limb consists of:
- Shoulder/Pectoral girdle - connects limb to trunk
- Arm (brachium) - shoulder to elbow
- Forearm (antebrachium) - elbow to wrist
- Hand - carpals, metacarpals, phalanges
All major structures (nerves, vessels, lymphatics) entering and leaving the upper limb pass through the axilla.
2. Bones of the Upper Limb
| Region | Bones |
|---|---|
| Shoulder girdle | Clavicle, Scapula |
| Arm | Humerus |
| Forearm | Radius (lateral), Ulna (medial) |
| Wrist | 8 Carpal bones (2 rows of 4) |
| Hand | 5 Metacarpals, 14 Phalanges |
Carpal bones (proximal to distal, lateral to medial):
- Proximal row: Scaphoid, Lunate, Triquetrum, Pisiform
- Distal row: Trapezium, Trapezoid, Capitate, Hamate
- Mnemonic: "Some Lovers Try Positions That They Can't Handle"
3. The Axilla
The axilla is the gateway to the upper limb - a pyramidal space between the neck and arm.
Boundaries:
- Apex (inlet): Between clavicle, scapula, and 1st rib - continuous with the neck
- Anterior wall: Pectoralis major and minor muscles
- Posterior wall: Subscapularis, teres major, latissimus dorsi
- Medial wall: Upper thoracic wall + serratus anterior
- Lateral wall: Intertubercular groove of humerus
- Floor (base): Axillary fascia and skin
Contents:
- Axillary artery (3 parts)
- Axillary vein
- Brachial plexus cords and branches
- Axillary lymph nodes
- Fat and connective tissue
4. Brachial Plexus (Most Important Topic!)
Formed by anterior rami of C5, C6, C7, C8, T1
Mnemonic for order: "Rugby Teams Drink Cold Beer" = Roots, Trunks, Divisions, Cords, Branches
4.1 Roots → Trunks
| Trunk | Root Formation |
|---|---|
| Superior trunk | C5 + C6 |
| Middle trunk | C7 alone |
| Inferior trunk | C8 + T1 |
- Roots and trunks pass between anterior and middle scalene muscles in the neck
- The inferior trunk lies on rib I, posterior to the subclavian artery
4.2 Trunks → Divisions
Each of the 3 trunks splits into anterior and posterior divisions (6 divisions total).
- No peripheral nerves come directly from the divisions.
- Anterior divisions → nerves for anterior (flexor) compartments
- Posterior divisions → nerves for posterior (extensor) compartments
4.3 Divisions → Cords
| Cord | Formation | Position | Spinal segments |
|---|---|---|---|
| Lateral cord | Anterior div. of superior + middle trunks | Lateral to axillary artery | C5-C7 |
| Medial cord | Anterior div. of inferior trunk | Medial to axillary artery | C8-T1 |
| Posterior cord | All 3 posterior divisions | Posterior to axillary artery | C5-T1 |
4.4 Branches (Terminal Nerves)
From Lateral Cord:
- Lateral pectoral nerve (C5-C7)
- Musculocutaneous nerve (C5-C7)
- Lateral root of median nerve
From Medial Cord:
- Medial pectoral nerve (C8-T1)
- Medial cutaneous nerve of arm (C8-T1)
- Medial cutaneous nerve of forearm (C8-T1)
- Ulnar nerve (C7-T1)
- Medial root of median nerve
From Posterior Cord (5 branches):
- Superior subscapular nerve (C5-C6) - subscapularis
- Thoracodorsal nerve (C6-C8) - latissimus dorsi
- Inferior subscapular nerve (C5-C6) - subscapularis + teres major
- Axillary nerve (C5-C6) - deltoid + teres minor
- Radial nerve (C5-T1) - all posterior compartment muscles
Important: The musculocutaneous nerve, lateral root of median, median nerve, medial root of median, and ulnar nerve form an "M" shape over the axillary artery - useful landmark in surgery.
5. Key Peripheral Nerves - Quick Summary
| Nerve | Origin | Motor Supply | Sensory Supply |
|---|---|---|---|
| Musculocutaneous | Lateral cord (C5-C7) | Anterior arm muscles (biceps, brachialis, coracobrachialis) | Lateral forearm skin |
| Median | Medial + lateral cords (C6-T1) | Most anterior forearm muscles; thenar muscles; 2 lateral lumbricals | Palmar surface of lateral 3½ digits |
| Ulnar | Medial cord (C7-T1) | Most intrinsic hand muscles; flexor carpi ulnaris; medial ½ FDP | Medial 1½ digits (palm + dorsum) |
| Radial | Posterior cord (C5-T1) | All posterior arm and forearm muscles | Posterior arm, forearm, dorsolateral hand |
| Axillary | Posterior cord (C5-C6) | Deltoid, teres minor | Upper lateral arm skin |
6. Arteries of the Upper Limb
Subclavian → Axillary → Brachial → Radial/Ulnar
Axillary Artery (3 parts, divided by pectoralis minor):
- 1st part (medial to pec minor): Superior thoracic artery
- 2nd part (behind pec minor): Thoracoacromial artery, lateral thoracic artery
- 3rd part (lateral to pec minor): Subscapular artery, anterior/posterior circumflex humeral arteries
Key branches in scapular region:
- Posterior circumflex humeral artery - exits axilla through quadrangular space with axillary nerve; supplies deltoid and glenohumeral joint
- Circumflex scapular artery - exits through triangular space; anastomoses in posterior scapular region
- Suprascapular artery - supplies supraspinatus and infraspinatus
7. Important Spaces (High-Yield!)
| Space | Boundaries | Contents |
|---|---|---|
| Quadrangular space | Teres minor (sup), teres major (inf), long head of triceps (med), surgical neck of humerus (lat) | Axillary nerve, posterior circumflex humeral artery |
| Triangular space | Teres minor (sup), teres major (inf), long head of triceps (lat) | Circumflex scapular artery |
| Triangular interval | Teres major (sup), long head of triceps (med), humerus/lateral head of triceps (lat) | Radial nerve, profunda brachii artery |
8. Brachial Plexus Injuries (Clinically Important)
| Injury | Damage | Muscles Lost | Deformity |
|---|---|---|---|
| Erb's palsy (upper trunk C5-C6) | Forceful separation of neck and shoulder (e.g., birth injury, motorcycle) | Deltoid, supraspinatus, biceps, brachialis | "Waiter's tip" - arm adducted, medially rotated, forearm pronated |
| Klumpke's palsy (lower trunk C8-T1) | Forceful upward pull of arm | Intrinsic hand muscles, long finger flexors | Claw hand; ± Horner's syndrome |
| Saturday night palsy | Radial nerve in spiral groove | Extensors of wrist and fingers | Wrist drop |
9. Quick Memory Aids
- "NAVEL" in axilla (lateral to medial): Nerve (musculocutaneous), Artery (axillary), Vein, Empty space, Lymphatics
- Median nerve - "Ape hand" deformity on injury (thenar wasting)
- Ulnar nerve - "Claw hand" on injury (ring + little fingers)
- Radial nerve - "Wrist drop" on injury
- Axillary nerve - Damaged in shoulder dislocation / surgical neck fracture
These notes cover the highest-yield upper limb topics for MBBS 1st year exams. All content is from Gray's Anatomy for Students. Let me know if you want notes on a specific sub-region - shoulder joint, rotator cuff, carpal tunnel, or muscles of the arm/forearm in detail!
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