Posterior Forearm Muscles

Question 0

Extensor carpi radialis longus Origin? Insertion? Innervation? Action?

Answer 0

O: Lateral supracondylar ridge of humerus

I: Dorsal aspect of base of 2nd metacarpal

Innervation: Radial nerve (C6,C7)

Action: Extension and radial deviation at the wrist joint

Question 1

Brachioradialis Origin? Insertion? Innervation? Action?

Answer 1

O: Proximal 2/3 of lateral supracondylar ridge of humerus

I: Lateral surface of distal end of radius proximal to styloid process

Innervation: Radial nerve (C5,C6,C7)

Action: Relatively weak flexion of forearm, maximal when forearm is in midpronated position.

Question 2

Extensor carpi radialis brevis Origin? Insertion? Innervation? Action?

Answer 2

O: Lateral epicondyle of humerus (common extensor origin)

I: Dorsal aspect of base of 3rd metacarpal

Innervation: Deep branch of radial nerve (C7,C8)

Action: Extension and radial deviation at wrist joint; active during fist clenching

Question 3

Extensor digitorum Origin? Insertion? Innervation? Action?

Answer 3

O: Lateral epicondyle of humerus (common extensor origin)

I: Extensor expansions of medial 4 fingers

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extends medial 4 fingers primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

Question 4

Extensor digiti minimi Origin? Insertion? Innervation? Action?

Answer 4

O: Lateral epicondyle of humerus

I: Extensor expansion of 5th finger

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extends 5th finger primarily at metacarpophalangeal joint, secondarily at interphalangeal joint

Question 5

Extensor carpi ulnaris Origin? Insertion? Innervation? Action?

Answer 5

O: Lateral epicondyle of humerus; posterior border of ulna via a shared aponeurosis

I: Dorsal aspect of base of 5th metacarpal

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extension and ulnar deviation at wrist joint (also active during fist clenching)

Question 6

Supinator Origin? Insertion? Innervation? Action?

Answer 6

O: Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna

I: Lateral, posterior, and anterior surfaces of proximal third of radius

Innervation: Deep branch of radial nerve (C7,C8)

Action: Supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed)

Question 7

Abductor pollicis longus Origin? Insertion? Innervation? Action?

Answer 7

O: Posterior surface of proximal halves of ulna, radius, and interosseous membrane

I: Base of 1st metacarpal

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Abducts thumb and extends it at carpometacarpal joint

Question 8

Extensor pollicis longus Origin? Insertion? Innervation? Action?

Answer 8

O: Posterior surface of middle third of ulna and interosseous membrane

I: Dorsal aspect of base of distal phalanx of thumb

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints

Question 9

Extensor pollicis brevis Origin? Insertion? Innervation? Action?

Answer 9

O: Posterior surface of distal third of radius and interosseous membrane

I: Dorsal aspect of base of proximal phalanx of thumb

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint

Question 10

Extensor indicis Origin? Insertion? Innervation? Action?

Answer 10

O: Posterior surface of distal third of ulna and interosseous membrane

I: Extensor expansion of 2nd finger

Innervation: Posterior interosseous nerve, a continuation of the deep branch of the radial nerve (C7,C8)

Action: Extends 2nd finger (enabling its independent extension); helps extend hand at wrist