Muscles of the Back of Forearm : Deep

Question 1

List the deep group of muscles found on the back of the forearm (5)

Answer 1

1. Supinator
2. Abductor pollicis longus
3. Extensor pollicis brevis
4. Extensor pollicis longus
5. Extensor indicis

Question 2

Origin of supinator (2)

Answer 2

has two different fibres:

1. Superficial fibres: Arise from lateral epicondyle, radial collateral and annular ligaments
2. Deep fibres: Arise from supinator fossa and crest of ulna

Question 3

Insertion of supinator

Answer 3

Into upper 1/3 of lateral surface of radius (between anterior and posterior oblique lines)

Question 4

Nerve supply of supinator

Answer 4

Posterior interosseous nerve
Supplies it in the cubital fossa then pierces it and curves backwards around neck of radius between the superficial and deep fibres to reach the back of forearm

Question 5

Actions of supinator (2)

Answer 5

1. Supination of forearm (in the extended position)
2. Fixation of radius to ulna (by the deep fibres)

Question 6

Origin of abductor policis longus (3)

Answer 6

1. Upper 1/3 of posterior surface of ulna
2. Middle 1/3 of posterior surface of radius
3. Back of the interosseous membrane

Question 7

Insertion of abductor pollicis longus

Answer 7

Lateral side of the base of the 1st metacarpal bone

Question 8

Nerve supply of abductor pollicis longus

Answer 8

Posterior interosseous nerve

Question 9

Actions of abductor pollicis longus

Answer 9

1. Abducts the thumb
2. Can extend the thumb
3. It can flex the wrist (only when other flexors are paralysed)

Question 10

Origin of Extensor pollicis brevis (2)

Answer 10

1. The distal 1/3 of posterior surface of radius
2. Back of the interosseous membrane

Question 11

Insertion of Extensor pollicis brevis

Answer 11

Into dorsum of the base of proximal phalanx of the thumb

Question 12

Nerve supply of Extensor pollicis brevis

Answer 12

Posterior interosseous nerve

Question 13

Action of Extensor pollicis brevis

Answer 13

Extension of the proximal phalanx of the thumb

Question 14

Origin of Extensor pollicis longus (2)

Answer 14

1. Middle 1/3 of the posterior surface of ulna
2. The adjoining part of the interosseous membrane

Question 15

Insertion of Extensor pollicis longus

Answer 15

Dorsum of base of the terminal phalanx of the thumb

Question 16

Nerve supply of Extensor pollicis longus

Answer 16

Posterior interosseous nerve

Question 17

Action of Extensor pollicis longus

Answer 17

Extension of all joints of the thumb

Question 18

Origin of Extensor Indicis (2)

Answer 18

1. Lower part of posterior surface of ulna
2. Interosseous membrane

Question 19

Insertion of Extensor Indicis

Answer 19

Joins the extensor expansion of the index finger

Question 20

Nerve supply of Extensor Indicis

Answer 20

Posterior interosseous nerve