Flexors and extensor muscles of upperlimb

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I now have comprehensive information from the THIEME Atlas to compile a thorough answer. Let me present it:

Flexors and Extensor Muscles of the Upper Limb

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

Overview

The upper limb muscles are organized by region: arm (brachium) and forearm (antebrachium). Almost all are innervated by the brachial plexus (C5–T1).

I. ARM MUSCLES

Anterior Compartment — Flexors

1. Biceps Brachii

Feature	Detail
Origin	Long head: supraglenoid tubercle of scapula; Short head: coracoid process of scapula
Insertion	Radial tuberosity + antebrachial fascia via bicipital aponeurosis
Actions	Elbow: flexion, supination (with elbow flexed); Shoulder: flexion, stabilization of humeral head
Innervation	Musculocutaneous nerve (C5–C7)

The biceps acts as a powerful supinator when the elbow is flexed — the tendon wraps around the radius like a rope around a crank.

2. Brachialis

Feature	Detail
Origin	Distal half of anterior surface of humerus + medial and lateral intermuscular septa
Insertion	Ulnar tuberosity
Action	Elbow joint: flexion (the "workhorse" flexor — pure flexor regardless of forearm position)
Innervation	Musculocutaneous nerve (C5–C7); small radial nerve branch (C5–C6)

3. Coracobrachialis

Feature	Detail
Origin	Coracoid process of scapula
Insertion	Humerus (in line with crest of lesser tubercle)
Actions	Shoulder: flexion, adduction, internal rotation
Innervation	Musculocutaneous nerve (C5–C7)

Posterior Compartment — Extensors

1. Triceps Brachii

Feature	Detail
Origin	Long head: infraglenoid tubercle of scapula; Medial head: posterior humerus, distal to radial groove; Lateral head: posterior humerus, proximal to radial groove
Insertion	Olecranon of ulna
Actions	Elbow joint: extension; Shoulder (long head): backward movement and adduction of arm
Innervation	Radial nerve (C6–C8)

2. Anconeus

Feature	Detail
Origin	Lateral epicondyle of humerus
Insertion	Olecranon of ulna (radial surface)
Actions	Extends elbow; tightens joint capsule
Innervation	Radial nerve (C6–C8)

II. FOREARM MUSCLES

Anterior Compartment — Flexors

Superficial Layer (all arise from the medial epicondyle — "common flexor origin")

Muscle	Insertion	Action	Nerve
Pronator teres	Lateral radius	Pronation; weak elbow flexion	Median (C6)
Flexor carpi radialis	Base of 2nd (±3rd) metacarpal	Wrist flexion, radial deviation	Median (C6–C8)
Palmaris longus	Palmar aponeurosis	Wrist palmar flexion	Median (C8–T1)
Flexor carpi ulnaris	Hamate, 5th metacarpal, pisiform	Wrist flexion, ulnar deviation	Ulnar nerve (C8–T1)
Flexor digitorum superficialis (FDS)	Sides of middle phalanges (2nd–5th digits)	Flexion of wrist, MCP, PIP joints	Median (C7–T1)

Deep Layer

Muscle	Origin	Insertion	Action	Nerve
Flexor digitorum profundus (FDP)	Anterior surface of ulna + interosseous membrane	Distal phalanges (2nd–5th digits)	Flexion of wrist, MCP, PIP, DIP joints	Medial half: Ulnar (C8–T1); Lateral half: AIN/Median (C8–T1)
Flexor pollicis longus (FPL)	Anterior radius + interosseous membrane	Distal phalanx of thumb	Flexion of IP joint of thumb	Anterior interosseous nerve/Median (C8–T1)
Pronator quadratus	Distal anterior ulna	Distal anterior radius	Pronation	Anterior interosseous nerve/Median (C8–T1)

Posterior Compartment — Extensors

Superficial Extensors (arise from lateral epicondyle — "common extensor origin")

Muscle	Insertion	Action	Nerve
Extensor digitorum	Dorsal digital expansion (2nd–5th digits)	Extension of wrist + MCP, PIP, DIP joints (2nd–5th)	Radial (C7–C8)
Extensor digiti minimi	Dorsal digital expansion (5th digit)	Extension + abduction of little finger	Radial (C7–C8)
Extensor carpi ulnaris	Base of 5th metacarpal	Wrist extension + ulnar deviation	Radial (C7–C8)

Deep Extensors

Muscle	Origin	Insertion	Action	Nerve
Supinator	Olecranon, lateral epicondyle, radial collateral & annular ligaments	Radius (between radial tuberosity and pronator teres insertion)	Supination	Radial (C7–C8)
Abductor pollicis longus (APL)	Dorsal radius, ulna, interosseous membrane	Base of 1st metacarpal	Thumb abduction; radial deviation of wrist	Radial (C7–C8)
Extensor pollicis brevis (EPB)	Posterior radius + interosseous membrane	Base of proximal phalanx of thumb	Thumb extension at MCP; wrist radial deviation	Radial (C7–C8)
Extensor pollicis longus (EPL)	Posterior ulna + interosseous membrane	Base of distal phalanx of thumb	Thumb extension at IP + MCP; wrist extension	Radial (C7–C8)
Extensor indicis	Posterior ulna + interosseous membrane	Dorsal digital expansion of index finger	Index finger extension (independent)	Radial (C7–C8)

Radial (Lateral) Group — "Mobile Wad"

Muscle	Origin	Insertion	Action	Nerve
Brachioradialis	Lateral distal humerus, lateral intermuscular septum	Styloid process of radius	Elbow flexion; semipronation	Radial (C5–C6)
Extensor carpi radialis longus (ECRL)	Lateral supracondylar ridge	Dorsal base of 2nd metacarpal	Wrist extension + radial deviation	Radial (C6–C7)
Extensor carpi radialis brevis (ECRB)	Lateral epicondyle	Dorsal base of 3rd metacarpal	Wrist extension + radial deviation	Radial (C7–C8)

Key Clinical Points

Concept	Note
Common flexor origin	Medial epicondyle — injury → medial epicondylitis ("golfer's elbow")
Common extensor origin	Lateral epicondyle — injury → lateral epicondylitis ("tennis elbow")
Radial nerve damage	Loss of wrist/finger extension → "wrist drop"
Median nerve damage	Loss of FDS, FDP (lateral), FPL → inability to flex index finger DIP ("OK sign" loss)
Ulnar nerve damage	Loss of FCU, FDP (medial) → weakened wrist flexion + ulnar deviation
Anatomical snuff box	Bounded by APL/EPB (radial) and EPL (ulnar)
FDS vs FDP	FDS flexes PIP; FDP flexes DIP — clinically tested separately

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