Posterior forearm muscles

Question 1

Brachioradialis

Answer 1

Origin - proximal two thirds of lateral supraepicondylar 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 supra-epicondylar ridge of humerus
Insertion - dorsal aspect of base of 2nd metacarpal
Innervation - radial nerve C6, C7
Action - extend and abduct wrist joint
- extensor carpi radialis brevis active during fist clenching

Question 3

Extensor carpi radialis brevis

Answer 3

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

Question 4

Extensor digitorum

Answer 4

Origin - lateral epicondyle of humerus (common extensor origin)
Insertion - extensor expansions of medial four fingers
Innervation - deep branch of radial nerve C7, C8
Action - extend wrist joint
- extend medial four fingers primarily at metacarpophalangeal j
joints, secondarily at interphalangeal joint

Question 5

Extensor digiti minimi

Answer 5

Origin - lateral epicondyle of humerus (common extensor origin)
Insertion - extensor expansion of 5th finger
Innervation- posterior interosseous nerve C7, C8, continuation of deep branch of radial nerve
Action - extends wrist joint
- extends 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 a 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 first clenching)

Question 7

Supinator

Answer 7

Origin - lateral epicondyle of humerus
- radial collateral and anular ligaments
- supinator fossa
- crest of ulna
Insertion - 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 8

Abductor pollicus longus

Answer 8

Origin - posterior surface of proximal halves 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 9

Extensor pollicus longus

Answer 9

Origin - posterior surface of middle third 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 joints
- extends metacarpophalangeal and carpometacarpal joints

Question 10

Extensor pollicus brevis

Answer 10

Origin - posterior surface of distal third 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
- extends carpometacarpal joint

Question 11

Extensor indicis

Answer 11

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 its independent extension
- helps extend hand at wrist