muscles of the dorsal forearm and dorsal hand

Question 1

brachioradialis

Answer 1

Origin: proximal 2/3s of lateral supracondylar ridge of humerus
Insertion: lateral surface of distal end of radius proximal to styloid process
Innervation: radial nerve (C5, C6, C7)
Action: relatively weak flexion of elbow joint, maximal when forearm is in midpronated position

Question 2

extensor carpi radialis longus

Answer 2

Origin: lateral supracondylar ridge of humerus
Insertion: dorsal aspect of base of 2nd metacarpal
Innervation: radial nerve (C6, C7)
Action: extend and abduct wrist joint, brevis active during fist clenching

Question 3

extensor carpi radialis brevis

Answer 3

Origin: lateral epicondyle of humerus
Insertion: dorsal aspect of base of 3rd metacarpal
Innervation: deep branch of radial nerve (C7, C8)
Action: extend and abduct wrist joint, brevis active during fist clenching

Question 4

extensor digitorum

Answer 4

Origin: lateral epicondyle of humerus
Insertion: extensor expansions of medial 4 fingers
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends wrist joint; extends medial 4 fingers primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

Question 5

extensor digiti minimi

Answer 5

Origin: lateral epicondyle of humerus
Insertion: extensor expansion of 5th finger
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extend wrist joint; extend 5th finger primarily at metacarpophalangeal joint, secondarily at interphalangeal joint

Question 6

extensor carpi ulnaris

Answer 6

Origin: lateral epicondyle of humerus; posterior border of ulna via shared aponeurosis
Insertion: dorsal aspect of base of 5th metacarpal
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends and adducts wrist joint (also active during fist clenching)

Question 7

abductor pollicis longus

Answer 7

Origin: posterior surface of proximal 1/2s of ulna, radius, and interosseous membrane
Insertion: base of 1st metacarpal
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends wrist joint; abducts thumb and extends it at carpometacarpal joint

Question 8

extensor pollicis longus

Answer 8

Origin: posterior surface of middle 1/3 of ulna and interosseous membrane
Insertion: dorsal aspect of base of distal phalanx of thumb
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends wrist joint; extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints

Question 9

extensor pollicis brevis

Answer 9

Origin: posterior surface of distal 1/3 of radius and interosseous membrane
Insertion: dorsal aspect of base of proximal phalanx of thumb
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends wrist joint; extends proximal phalanx of thumb at metacarpophalangeal joint and carpometacarpal joint

Question 10

extensor indicis

Answer 10

Origin: posterior surface of distal third of ulna and interosseous membrane
Insertion: extensor expansion of 2nd finger
Innervation: posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve
Action: extends wrist joint; extends 2nd finger (enabling independent extension), helps extend hand at wrist

Question 11

supinator

Answer 11

Origin: lateral epicondyle of humerus, radial collateral and anular ligaments, supinator fossa, crest of ulna
Insertion: lateral, posterior, and anterior surfaces of proximal 1/3 of radius
Innervation: deep branch of radial nerve (C7, C8)
Action: supinates forearm