upper limb muscles
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anatomy diagram of upper limb muscles shoulder arm forearm anterior posterior labeled
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Upper limb muscles: high-yield classification
Upper-limb muscles are best organized regionally. Most are supplied by the brachial plexus (C5-T1). Important exceptions include trapezius, sternocleidomastoid, and omohyoid. - General Anatomy and Musculoskeletal System (THIEME Atlas), p. 317
1. Shoulder girdle muscles
These position and stabilize the scapula.
| Group | Muscles | Main actions |
|---|---|---|
| Posterior | Trapezius, levator scapulae, rhomboid major, rhomboid minor | Elevate, retract, rotate, and stabilize scapula |
| Anterior | Serratus anterior, pectoralis minor, subclavius | Protract and stabilize scapula; serratus anterior assists upward rotation |
| Related muscle | Sternocleidomastoid, omohyoid | Act on head/neck or hyoid, but are regionally related |
Clinical point: Long thoracic nerve injury weakens serratus anterior and may cause a winged scapula.
2. Shoulder joint muscles
Rotator cuff: SITS
- Supraspinatus: initiates abduction
- Infraspinatus: lateral rotation
- Teres minor: lateral rotation
- Subscapularis: medial rotation
Other major shoulder movers:
- Deltoid: major abductor after the first 15 degrees
- Pectoralis major: flexion, adduction, medial rotation
- Latissimus dorsi: extension, adduction, medial rotation
- Teres major: adduction and medial rotation
- Coracobrachialis: flexion and adduction of arm
3. Arm muscles
| Compartment | Muscles | Main action | Main nerve |
|---|---|---|---|
| Anterior | Biceps brachii, brachialis, coracobrachialis | Elbow flexion; biceps also supinates forearm | Musculocutaneous |
| Posterior | Triceps brachii, anconeus | Elbow extension | Radial |
4. Forearm muscles
Anterior compartment: flexor-pronator group
Mainly flexes the wrist and fingers and pronates the forearm.
- Superficial: pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris
- Intermediate: flexor digitorum superficialis
- Deep: flexor digitorum profundus, flexor pollicis longus, pronator quadratus
Innervation: mostly median nerve.
Exceptions: flexor carpi ulnaris and medial half of flexor digitorum profundus are supplied by the ulnar nerve.
Exceptions: flexor carpi ulnaris and medial half of flexor digitorum profundus are supplied by the ulnar nerve.
Posterior compartment: extensor-supinator group
Mainly extends wrist/fingers and supinates the forearm.
- Superficial: extensor digitorum, extensor digiti minimi, extensor carpi ulnaris
- Deep: supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis
- Lateral/radial group: brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis
Innervation: radial nerve and its deep branch/posterior interosseous nerve.
5. Intrinsic hand muscles
| Group | Muscles | Main actions |
|---|---|---|
| Thenar | Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, adductor pollicis | Thumb abduction, flexion, opposition, adduction |
| Hypothenar | Abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, palmaris brevis | Little-finger movements |
| Lumbricals | Four lumbricals | Flex MCP joints, extend IP joints |
| Interossei | Four dorsal and three palmar interossei | Dorsal interossei abduct, palmar interossei adduct fingers |
Memory aid:
- DAB: Dorsal interossei ABduct
- PAD: Palmar interossei ADduct
Most intrinsic hand muscles are supplied by the ulnar nerve. Median nerve supplies the thenar muscles and first two lumbricals.
The regional grouping and listed muscles align with General Anatomy and Musculoskeletal System (THIEME Atlas), pp. 316-317. A useful external upper-limb muscle overview includes labelled regional diagrams.
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