Muscles of the Posterior Forearm

Question 1

Superficial muscles

Answer 1

Brachioradialis, extensor carpi radialis brevis, extensor carpi radialis longus, extensor digitorum, extensor carpi ulnaris, extensor digiti minimi, anconeus

Question 2

Brachioradialis

Answer 2

Paradoxical muscle as it has the characteristics of an extensor muscle but actually flexes at the elbow
Origin - proximal aspect of the lateral supracondylar ridge of humerus
Attachment - distal end of the radius, just before the radial styloid process
Action - flexes elbow
Innervation - radial nerve

Question 3

Extensor carpi radialis longus

Answer 3

Origin - supracondylar ridge
Attachment - metacarpal bones II and III
Action - extends and abducts the wrist
Innervation - radial nerve

Question 4

Extensor carpi radialis brevis

Answer 4

Origin - lateral epicondyle
Attachment - metacarpal bones II and III
Action - extends and abducts the wrist
Innervation - radial nerve

Question 5

Extensor digitorum

Answer 5

Origin - lateral epicondyle
Attachment - extensor hood of each finger
Action - extends medial four fingers at the metacarpophalangeal and interphalangeal joint
Innervation - radial nerve

Question 6

Extensor digiti minimi

Answer 6

Origin - lateral epicondyle of humerus
Attachment - extensor hood of little finger
Action - extends little finger and contributes to wrist extension
Innervation - radial nerve

Question 7

Anconeus

Answer 7

Origin - lateral epicondyle
Attachment - lateral part of the olecranon
Action - moves ulna during pronation and extends elbow joint
Innervation - radial nerve

Question 8

Extensor carpi ulnaris

Answer 8

Origin - lateral epicondyle of humerus
Attachment - base of metacarpal V
Action - extension and adduction of the wrist
Innervation - radial nerve

Question 9

Deep muscles

Answer 9

Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis proprius

Question 10

Supinator

Answer 10

Origin - lateral epicondyle of humerus and posterior surface of ulna
Attachment - posterior surface of radius
Action - supinates the forearm
Innervation - radial nerve

Question 11

Abductor pollicis longus

Answer 11

Origin - interosseous membrane and adjacent posterior surfaces of the radius and ulna
Attachment - lateral side of the base of metacarpal I
Action - abducts the thumb
Innervation - radial nerve

Question 12

Extensor pollicis brevis

Answer 12

Origin - posterior surface of radius and interosseous membrane
Attachment - base of the proximal phalanx of the thumb
Action - extends the metacarpophalangeal and carpometacarpal joints of the thumb
Innervation - radial nerve

Question 13

Extensor pollicis longus

Answer 13

Origin - posterior surface of the ulna and interosseous membrane
Attachment - distal phalanx of the thumb
Action - extends all the joints of the thumb: carpometacarpal, metacarpophalangeal and interphalangeal
Innervation - radial nerve

Question 14

Extensor indicis proprius

Answer 14

Origin - posterior surface of the ulna and interosseous membrane, distal to extensor policies longus
Attachment - extensor hood of index finger
Innervation - radial nerve

Question 15

Wrist drop

Answer 15

Radial nerve injury occurring proximal to the elbow
Two common sites - axilla and radial groove of the humerus
Axilla - injured via humeral dislocations or fractures of the proximal humerus
Radial groove of humerus - injured via a humeral shaft fracture
Extensor muscles paralysed, flexion is innervated by the median nerve and so unopposed flexion occurs at the wrist joint