Muscle Origins and Actions (Weeks 5-9)

Vocabulary flashcards summarizing key muscles of the foot, shoulder, arm, forearm, and hand—including their primary actions and innervation—to aid Week 5-9 exam review.

Abductor hallucis

Origin: Medial tubercle of calcaneus, flexor retinaculum, plantar aponeurosis. Insertion: Medial side of base of proximal phalanx of great toe. Action: Abducts and flexes the great toe. Innervation: medial plantar nerve.

Flexor digitorum brevis

Origin: Medial tubercle of calcaneus, central part of plantar aponeurosis. Insertion: Sides of middle phalanges of toes 2-5. Action: Flexes toes 2-5 at MTP and IP joints. Innervation: medial plantar nerve.

Abductor digiti minimi (foot)

Origin: Lateral tubercle and medial tubercle of calcaneus, plantar aponeurosis. Insertion: Lateral side of base of proximal phalanx of 5th toe. Action: Abducts and flexes the 5th toe. Innervation: lateral plantar nerve.

Quadratus plantae

Origin: Medial and lateral surfaces of calcaneus. Insertion: Lateral border of tendon of flexor digitorum longus. Action: Assists flexor digitorum longus in flexing toes 2-5. Innervation: lateral plantar nerve.

Lumbricals (foot)

Origin: Tendons of flexor digitorum longus. Insertion: Medial side of proximal phalanges, extensor expansion of toes 2-5. Action: Flex MTP and extend IP joints of toes 2-5. Innervation: 1st = medial plantar nerve, others = lateral plantar nerve.

Flexor hallucis brevis

Origin: Cuboid, lateral cuneiform, tendon of tibialis posterior. Insertion: Both sides of base of proximal phalanx of great toe. Action: Flexes proximal phalanx of the great toe. Innervation: medial plantar nerve.

Adductor hallucis

Origin: Oblique head: bases of metatarsals 2-4, cuboid, lateral cuneiform; Transverse head: plantar ligaments of MTP joints 3-5. Insertion: Lateral side of base of proximal phalanx of great toe. Action: Adducts great toe and supports transverse arch. Innervation: deep branch of lateral plantar nerve.

Flexor digiti minimi brevis (foot)

Origin: Base of metatarsal 5, fibularis longus tendon sheath. Insertion: Lateral side of base of proximal phalanx of 5th toe. Action: Flexes proximal phalanx of 5th toe. Innervation: superficial branch of lateral plantar nerve.

Deltoid

Origin: Lateral third of clavicle, acromion, spine of scapula. Insertion: Deltoid tuberosity of humerus. Action: Anterior fibers flex/medially rotate, middle fibers abduct, posterior fibers extend/laterally rotate arm. Innervation: axillary nerve.

Teres major

Origin: Posterior surface of inferior angle of scapula. Insertion: Medial lip of intertubercular sulcus of humerus. Action: Adducts and medially rotates arm. Innervation: lower subscapular nerve.

Supraspinatus

Origin: Supraspinous fossa of scapula. Insertion: Greater tubercle of humerus (superior facet). Action: Initiates arm abduction and stabilizes shoulder (rotator cuff). Innervation: suprascapular nerve.

Infraspinatus

Origin: Infraspinous fossa of scapula. Insertion: Greater tubercle of humerus (middle facet). Action: Laterally rotates arm and stabilizes shoulder. Innervation: suprascapular nerve.

Teres minor

Origin: Middle part of lateral border of scapula. Insertion: Greater tubercle of humerus (inferior facet). Action: Laterally rotates arm and stabilizes shoulder. Innervation: axillary nerve.

Subscapularis

Origin: Subscapular fossa. Insertion: Lesser tubercle of humerus. Action: Medially rotates arm and holds humeral head in glenoid. Innervation: upper & lower subscapular nerves.

Biceps brachii

Origin: Short head: Coracoid process; Long head: Supraglenoid tubercle of scapula. Insertion: Radial tuberosity, bicipital aponeurosis. Action: Supinates and flexes forearm; short head resists shoulder dislocation. Innervation: musculocutaneous nerve.

Brachialis

Origin: Anterior surface of humerus. Insertion: Tuberosity and coronoid process of ulna. Action: Primary flexor of forearm in all positions. Innervation: musculocutaneous and radial nerves.

Coracobrachialis

Origin: Coracoid process of scapula. Insertion: Medial surface of mid-shaft of humerus. Action: Helps flex and adduct arm; resists shoulder dislocation. Innervation: musculocutaneous nerve.

Brachioradialis

Origin: Lateral supracondylar ridge of humerus. Insertion: Styloid process of radius. Action: Weak forearm flexor, strongest in mid-pronation. Innervation: radial nerve.

Triceps brachii

Origin: Long head: Infraglenoid tubercle of scapula; Lateral head: Posterior surface of humerus superior to radial groove; Medial head: Posterior surface of humerus inferior to radial groove. Insertion: Olecranon of ulna. Action: Chief extensor of forearm; long head stabilizes humerus. Innervation: radial nerve.

Pronator teres

Origin: Humeral head: Medial epicondyle of humerus; Ulnar head: Coronoid process of ulna. Insertion: Lateral surface of radius (mid-shaft). Action: Pronates and flexes forearm. Innervation: median nerve.

Flexor carpi radialis

Origin: Medial epicondyle of humerus. Insertion: Base of metacarpals 2 & 3. Action: Flexes and abducts hand at wrist. Innervation: median nerve.

Palmaris longus

Origin: Medial epicondyle of humerus. Insertion: Palmar aponeurosis. Action: Flexes wrist and tenses palmar aponeurosis. Innervation: median nerve.

Flexor carpi ulnaris

Origin: Humeral head: Medial epicondyle of humerus; Ulnar head: Olecranon and posterior border of ulna. Insertion: Pisiform, hook of hamate, base of metacarpal 5. Action: Flexes and adducts hand at wrist. Innervation: ulnar nerve.

Flexor digitorum superficialis

Origin: Humero-ulnar head: Medial epicondyle of humerus, coronoid process, ulna; Radial head: Oblique line of radius. Insertion: Sides of middle phalanges of digits 2-5. Action: Flexes middle and proximal phalanges of digits 2-5. Innervation: median nerve.

Flexor digitorum profundus

Origin: Anterior and medial surfaces of ulna, interosseous membrane. Insertion: Bases of distal phalanges of digits 2-5. Action: Flexes distal phalanges (digits 2-5). Innervation: medial half = ulnar nerve, lateral half = anterior interosseous (median).

Flexor pollicis longus

Origin: Anterior surface of radius, interosseous membrane. Insertion: Base of distal phalanx of thumb. Action: Flexes phalanges of the thumb. Innervation: anterior interosseous nerve (median).

Pronator quadratus

Origin: Anterior surface of distal ulna. Insertion: Anterior surface of distal radius. Action: Primary forearm pronator; binds radius and ulna. Innervation: anterior interosseous nerve.

Extensor carpi radialis brevis

Origin: Lateral epicondyle of humerus. Insertion: Base of metacarpal 3. Action: Extends and abducts wrist. Innervation: deep branch of radial nerve.

Extensor digitorum (communis)

Origin: Lateral epicondyle of humerus. Insertion: Extensor expansions of digits 2-5. Action: Extends digits 2-5 at MTP and IP joints. Innervation: deep branch of radial nerve.

Extensor digiti minimi

Origin: Lateral epicondyle of humerus (common extensor origin). Insertion: Extensor expansion of little finger. Action: Extends little finger at MTP and IP joints. Innervation: deep branch of radial nerve.

Extensor carpi ulnaris

Origin: Lateral epicondyle of humerus (humeral head), posterior border of ulna (ulnar head). Insertion: Base of metacarpal 5. Action: Extends and adducts wrist. Innervation: deep branch of radial nerve.

Extensor carpi radialis longus

Origin: Lateral supracondylar ridge of humerus. Insertion: Base of metacarpal 2. Action: Extends and abducts wrist, active during fist clenching. Innervation: radial nerve.

Abductor pollicis longus

Origin: Posterior surfaces of ulna, radius, and interosseous membrane. Insertion: Base of metacarpal 1. Action: Abducts thumb and extends carpometacarpal joint. Innervation: posterior interosseous nerve.

Extensor pollicis longus

Origin: Posterior surface of ulna, interosseous membrane. Insertion: Base of distal phalanx of thumb. Action: Extends distal phalanx of thumb at IP, MTP, and CMC joints. Innervation: posterior interosseous nerve.

Extensor pollicis brevis

Origin: Posterior surface of radius, interosseous membrane. Insertion: Base of proximal phalanx of thumb. Action: Extends proximal phalanx of thumb at MTP and CMC joints. Innervation: posterior interosseous nerve.

Supinator

Origin: Lateral epicondyle of humerus, radial collateral ligament, annular ligament, supinator crest of ulna. Insertion: Anterior, lateral, and posterior surfaces of proximal radius. Action: Supinates forearm by rotating radius. Innervation: deep branch of radial nerve.

Extensor indicis

Origin: Posterior surface of ulna, interosseous membrane. Insertion: Extensor expansion of index finger. Action: Extends index finger and assists wrist extension. Innervation: posterior interosseous nerve.

Abductor pollicis brevis

Origin: Flexor retinaculum, scaphoid, trapezium. Insertion: Lateral side of base of proximal phalanx of thumb. Action: Abducts thumb and assists opposition. Innervation: recurrent branch of median nerve.

Flexor pollicis brevis

Origin: Superficial head: Flexor retinaculum, trapezium; Deep head: Trapezoid, capitate. Insertion: Lateral side of base of proximal phalanx of thumb. Action: Flexes thumb at MTP joint. Innervation: superficial head via recurrent median nerve.

Opponens pollicis

Origin: Flexor retinaculum, trapezium. Insertion: Lateral border of metacarpal 1. Action: Opposes thumb by medially rotating and flexing 1st metacarpal. Innervation: recurrent median nerve.

Abductor digiti minimi (hand)

Origin: Pisiform, flexor carpi ulnaris tendon, pisohamate ligament. Insertion: Medial side of base of proximal phalanx of 5th digit. Action: Abducts 5th digit and assists its flexion. Innervation: deep branch of ulnar nerve.

Flexor digiti minimi brevis (hand)

Origin: Hook of hamate, flexor retinaculum. Insertion: Medial side of base of proximal phalanx of 5th digit. Action: Flexes proximal phalanx of 5th digit. Innervation: deep branch of ulnar nerve.

Opponens digiti minimi

Origin: Hook of hamate, flexor retinaculum. Insertion: Medial border of metacarpal 5. Action: Draws 5th metacarpal forward and rotates it for opposition. Innervation: deep branch of ulnar nerve.

Adductor pollicis

Origin: Oblique head: Bases of metacarpals 2 & 3, capitate; Transverse head: Anterior surface of metacarpal 3. Insertion: Medial side of base of proximal phalanx of thumb. Action: Adducts thumb toward palm. Innervation: deep branch of ulnar nerve.

Lumbricals (hand)

Origin: Tendons of flexor digitorum profundus. Insertion: Lateral sides of extensor expansions of digits 2-5. Action: Flex MCP and extend IP joints of digits 2-5. Innervation: 1-2 = median nerve, 3-4 = deep ulnar nerve.