muscles of posterior compartment of forearm

Question 1

superficial layer

Answer 1

all supplied by radial nerve except for extensor carpi ulnas (ECU) supplied by posterior interosseous nerve

Question 2

Answer 2

Brachioradialis

• *proximal attachment**: proximal two thirds of lateral supra-epicondylar ridge of humerus
• *distal attachment** : lateral surface of distal end of radius proximal to styloid process
• *main action** : relatively weak flexion of elbow joint, maximal when forearm is in midpronated position
• *innervation** : radial nerve (C5,C6, C7)

Question 3

Answer 3

extensor carpi radialis longus (ECRL)

proximal attachment : lateral supra-epicondylar ridge of humerus

distal attachment : dorsal aspect of base of 2nd metacarpal

main action : extends and abducts writ joint; extends carpometacarpal joints

innervation : radial nerve (C6,C7)

Question 4

Answer 4

extensor carpi radialis brevis (ECRB)

proximal attachment : lateral epicondyle of humerus (common extensor origin)

distal attachment : dorsal aspect of base of 3rd metacarpal

main action : extends and abducts wrist joint; extends carpometacarpal joints. active during fist clenching

innervation : deep branch of radial nerve (C7, C8)

Question 5

Answer 5

extensor digitorum

proximal attachment : lateral epicondyle of humerus (common extensor origin)

distal attachment : extensor expansions of medial four fingers

main action: extends wrist joint, carpometacarpal joints. extends medial four fingers primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

innervation : posterior interosseous nerve (C7,C8), continuation of deep branch of radial nerve

Question 6

Answer 6

extensor digiti minimi (EDM)

proximal attachment : lateral epicondyle of humerus

distal attachment: extensor expansion of 5th finger

main action : extends wrist joint, carpometacarpal joints. extends 5th finger primarily at metacarpophalangeal joint, secondarily at interphalangeal joints

innervation : posterior interosseous nerve (C7, C8,) continuation of deep branch of radial nerve

Question 7

Answer 7

extensor carpi ulnaris (ECU)

proximal attachment: lateral epicondyle of humerus; posterior border of ulna via a shared aponeurosis

distal attachment: dorsal aspects of base of 5th metacarpal

main action: extends and adducts wrist joint, carpometacarpal joints (active during fist clenching)

innervation: posterior interosseous nerve (C7, C8)

Question 8

deep layer

Question 9

Answer 9

supinator

proximal attachment : lateral epicondyle of humerus, radial collateral and angular ligaments, supinator fossa, crest of ulna

distal attachment : lateral, posterior and anterior surfaces of proximal third of radius

main action : supinates forearm; rotates radius to turn palm anteriorly or superiorly

innervation : deep branch of radial nerve (C7, C8)

Question 10

“outcropping” muscles of deep layer

Answer 10

innovated by posterior interosseous nerve

Question 11

Answer 11

abductor pollicis longus (APL)

proximal attachment : posterior surface of proximal halves of ulna, radius and interosseous membrane

distal attachment : base of 1st metacarpal

main action : extends wrist joint, carpometacarpal joints. abducts thumb and extends it at carpometacarpal joint

innervation : posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve

Question 12

Answer 12

extensor pollicis longus (EPL)

Proximal attachments : posterior surfaces of middle third of ulna and interosseous membrane

distal attachments : dorsal aspect of base of distal phalanx of thumb

main action : extends wrist joint, carpometacarpal joints. extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints

innervation : posterior interosseous nerve (C7, C8)

Question 13

Answer 13

extensor pollicis brevis (EPB)

proximal attachments : posterior surface of distal third of radius and interosseous membrane

distal attachments : dorsal aspect of base of proximal phalanx of thumb

main action : extends wrist joint, carpometacarpal joints. extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint

innervation : posterior interosseous nerve (C7, C8)

Question 14

Answer 14

extensor indicis

proximal attachment : posterior surfaces of distal third of ulna and interosseous membrane

distal attachments : extensor expansion of 2nd finger

main action : extends wrist joint, carpometacarpal joints. extend 2nd finger, helps extend hand at wrist

innervation : posterior interosseous nerve ( C7, C8)

Question 15

see lectures 14 and 15

Question 16

Muscles that extend and adduct/abduct the hand at the wrist joint

Answer 16

extensor carpi radialis longus (ECRL)

Extensor carpi radialis brevis (ECRB)

Extensor carpi ulnaris (ECU)

Question 17

muscles that extend the medial four digits

Answer 17

extensor digitorum, extensor indicis, extensor digiti minimi (EDM)

Question 18

muscles that extend or abduct the thumb

Answer 18

Abductor pollicis longus (APL)

extensor pollicis Brevis (EPB)

extensor pollicis longus (EPL)