Muscles of upperlimb

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Muscles of the Upper Limb

Source: THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System

The muscles of the upper limb are classified by topography and function into five regional groups, and by innervation (almost entirely via the brachial plexus, C5-T1).

1. Muscles of the Shoulder Girdle

These connect the axial skeleton to the shoulder girdle and position the scapula.

A. Migrated from the head (cranial nerve XI + cervical plexus)

Muscle	Nerve
Trapezius	Accessory nerve (CN XI)
Sternocleidomastoid	Accessory nerve (CN XI)
Omohyoid	Ansa cervicalis

B. Posterior trunk and shoulder girdle muscles (Dorsal scapular nerve, C4-C5)

Muscle	Origin	Insertion	Action
Levator scapulae	Transverse processes C1-C4	Superior angle of scapula	Elevates scapula, inclines neck
Rhomboid minor	Spinous processes C6-C7	Medial border of scapula (above spine)	Retracts and elevates scapula
Rhomboid major	Spinous processes T1-T4	Medial border of scapula (below spine)	Retracts and elevates scapula

C. Anterior trunk and shoulder girdle muscles

Muscle	Nerve	Action
Subclavius	Nerve to subclavius (C5, C6)	Steadies clavicle at SC joint
Pectoralis minor	Medial & lateral pectoral nerves (C8, T1)	Draws scapula down, rotates glenoid inferiorly
Serratus anterior	Long thoracic nerve (C5-C7)	Protracts & rotates scapula (glenoid upward); "boxer's muscle"

2. Muscles of the Shoulder Joint

A. Rotator Cuff (SITS)

Four muscles stabilize the glenohumeral joint by compressing the humeral head into the glenoid:

Muscle	Origin	Insertion	Action	Nerve
Supraspinatus	Supraspinous fossa	Greater tubercle (superior facet)	Initiates abduction (0-15°)	Suprascapular (C5, C6)
Infraspinatus	Infraspinous fossa	Greater tubercle (middle facet)	External rotation	Suprascapular (C5, C6)
Teres minor	Lateral border of scapula	Greater tubercle (inferior facet)	External rotation, adduction	Axillary nerve (C5, C6)
Subscapularis	Subscapular fossa	Lesser tubercle	Internal rotation, adduction	Subscapular nerves (C5-C7)

B. Other Posterior Shoulder Muscles

Muscle	Origin	Insertion	Action	Nerve
Deltoid (3 parts)	Clavicle (lat. 1/3), acromion, scapular spine	Deltoid tuberosity of humerus	Abduction (acromial); flexion/IR (clavicular); extension/ER (spinal)	Axillary nerve (C5, C6)
Latissimus dorsi	T7-L5 spinous processes, iliac crest, ribs 9-12	Intertubercular groove of humerus	Extension, adduction, internal rotation of arm	Thoracodorsal nerve (C6-C8)
Teres major	Inferior angle of scapula	Intertubercular groove (medial lip)	Adduction, extension, internal rotation	Subscapular nerve (C5, C6)

C. Anterior Shoulder Muscles

Muscle	Origin	Insertion	Action	Nerve
Pectoralis major	Clavicle, sternum, ribs 1-6	Greater tubercle (lateral lip of groove)	Adduction, internal rotation, flexion	Medial & lateral pectoral nerves (C5-T1)
Coracobrachialis	Coracoid process	Medial shaft of humerus	Flexion and adduction of shoulder	Musculocutaneous nerve (C6, C7)

3. Muscles of the Arm

Anterior (Flexor) Compartment - Musculocutaneous nerve (C5-C7)

Muscle	Origin	Insertion	Action
Biceps brachii (long head)	Supraglenoid tubercle	Radial tuberosity, bicipital aponeurosis	Elbow flexion, supination (most powerful supinator)
Biceps brachii (short head)	Coracoid process	Same	Elbow flexion, shoulder flexion
Brachialis	Anterior distal humerus	Ulnar tuberosity and coronoid process	Elbow flexion (pure flexor - works in all positions)

Posterior (Extensor) Compartment - Radial nerve (C6-C8)

Muscle	Origin	Insertion	Action
Triceps brachii (long head)	Infraglenoid tubercle of scapula	Olecranon process of ulna	Elbow extension, shoulder extension/adduction
Triceps brachii (lateral head)	Posterior humerus (above radial groove)	Olecranon	Elbow extension
Triceps brachii (medial head)	Posterior humerus (below radial groove)	Olecranon	Elbow extension
Anconeus	Lateral epicondyle of humerus	Lateral olecranon	Assists extension, stabilizes elbow

4. Muscles of the Forearm

Anterior (Flexor) Compartment

Superficial layer (common origin: medial epicondyle) - Median nerve (except FCU):

Muscle	Insertion	Action	Nerve
Pronator teres	Lateral radius	Pronation, weak elbow flexion	Median (C6)
Flexor carpi radialis	Base of 2nd metacarpal	Wrist flexion, radial deviation	Median (C6, C7)
Palmaris longus	Palmar aponeurosis	Wrist flexion, tightens palmar fascia	Median (C7, C8)
Flexor digitorum superficialis	Middle phalanges of digits 2-5	Flexion at PIP, MCP, and wrist	Median (C7, C8, T1)
Flexor carpi ulnaris	Pisiform, hamate, 5th metacarpal	Wrist flexion, ulnar deviation	Ulnar nerve (C7, C8)

Deep layer - Median/Ulnar nerves:

Muscle	Insertion	Action	Nerve
Flexor digitorum profundus	Distal phalanges of digits 2-5	Flexion at DIP, PIP, MCP, wrist	Median (digits 2-3), Ulnar (digits 4-5)
Flexor pollicis longus	Distal phalanx of thumb	Thumb IP and MCP flexion	Median/AIN (C8, T1)
Pronator quadratus	Distal anterior ulna → radius	Pronation	Median/AIN (C8, T1)

Radial (Lateral) Group - Radial nerve:

Muscle	Action	Nerve
Brachioradialis	Elbow flexion, semipronation	Radial (C5, C6)
Extensor carpi radialis longus	Wrist extension, radial deviation	Radial (C6, C7)
Extensor carpi radialis brevis	Wrist extension, stabilizes fist	Radial/PIN (C7, C8)

Posterior (Extensor) Compartment - Radial nerve/PIN (C7, C8):

Superficial extensors:

Muscle	Action
Extensor digitorum	Extension of digits 2-5 at all finger joints
Extensor digiti minimi	Extension of little finger
Extensor carpi ulnaris	Wrist extension, ulnar deviation

Deep extensors:

Muscle	Action
Supinator	Supination of forearm
Abductor pollicis longus	Thumb abduction and extension at CMC
Extensor pollicis brevis	Extension of thumb MCP
Extensor pollicis longus	Extension of thumb IP (crosses anatomical snuffbox)
Extensor indicis	Independent extension of index finger

5. Intrinsic Muscles of the Hand

Thenar Muscles (ball of thumb) - Median nerve (C8, T1):

Muscle	Action
Abductor pollicis brevis	Abducts thumb
Flexor pollicis brevis	Flexes thumb MCP (superficial head - median; deep head - ulnar)
Opponens pollicis	Opposition of thumb (CMC)
Adductor pollicis	Adducts thumb

Hypothenar Muscles (ball of little finger) - Ulnar nerve (C8, T1):

Muscle	Action
Abductor digiti minimi	Abducts and flexes little finger
Flexor digiti minimi brevis	Flexes little finger at MCP
Opponens digiti minimi	Opposition of little finger
Palmaris brevis	Tightens palmar aponeurosis

Metacarpal (Intrinsic) Muscles:

Muscle	Count	Innervation	Action
Lumbricals	4	1st & 2nd: Median; 3rd & 4th: Ulnar	MCP flexion + IP extension ("intrinsic plus" position)
Dorsal interossei	4 (bipennate)	Ulnar (C8, T1)	DAB - Digit ABduction; also MCP flex, IP extend
Palmar interossei	3	Ulnar (C8, T1)	PAD - digit ADduction; MCP flex, IP extend

Innervation Summary (Brachial Plexus C5-T1)

Brachial plexus and nerve supply of the upper limb

Nerve	Key Muscles
Dorsal scapular	Levator scapulae, Rhomboids
Suprascapular	Supraspinatus, Infraspinatus
Long thoracic	Serratus anterior
Axillary	Deltoid, Teres minor
Musculocutaneous	Biceps brachii, Brachialis, Coracobrachialis
Radial	Triceps, Anconeus, Brachioradialis, all extensors of forearm
Median	Pronators, most flexors, thenar muscles (lateral 2 lumbricals)
Ulnar	FCU, medial FDP, all interossei, hypothenar, adductor pollicis, medial 2 lumbricals

Clinical Pearls

Injury	Muscle/Nerve affected	Key deficit
Axillary nerve damage (shoulder dislocation)	Deltoid, Teres minor	Loss of arm abduction
Long thoracic nerve	Serratus anterior	Winged scapula
Radial nerve (humeral shaft #)	Extensors	Wrist drop
Median nerve (carpal tunnel)	Thenar muscles (APB, OP)	Ape thumb deformity
Ulnar nerve (medial epicondyle)	Interossei, Hypothenar	Claw hand (digits 4-5)
Suprascapular nerve	Supraspinatus → Infraspinatus	Loss of initiation of abduction + ER
Rotator cuff tear (supraspinatus most common)	SITS muscles	Painful arc 60-120°, inability to sustain abduction

- THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System

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