Muscles of the Shoulder Girdle - Actions

Question 1

Trapezius - action

Answer 1

Upper: Elevates and upwardly rotates scapula, slightly retracts
Middle: retracts scapula
Lower: depresses and upwardly rotates scapula

Question 2

Levator scapulae - action

Answer 2

Elevates and downwardly rotates the scapula

Reverse origin: Laterally flexes the cervical spine

Question 3

Sternocleidomastoid - action

Answer 3

Provides dynamic support for flexion and extension of the neck and head

Bilaterally: Flexes head
Unilaterally: Laterally flexes the head to same side and contralaterally (opposite side) rotates the cervical spine

Reverse origin: sternal head can elevate the sternum; clavicular head elevates the clavicle

Question 4

Rhomboid Minor and Major - action

Answer 4

Retracts and rotates scapula
When at or below anatomical position elevates the scapula
Reverse origin acting unilaterally: laterally flex the spine (not usually used)
Fix scapula to thoracic wall with serratus anterior

Question 5

Serratus anterior - action

Answer 5

Protracts the scapula
Lower part depresses and upwardly rotates the scapula
Stabilize the scapula against the thoracic wall

Question 6

Pectoralis minor - action

Answer 6

Depresses, protracts and downwardly rotates the scapula
Reverse origin: pulls chest towards scapula
Reverse origin: can assist with forced inhalation by pulling ribs up and out

Question 7

Subclavis

Answer 7

Stabilizes clavicle in sternoclavicular joint
Weakly depresses the clavicle
*functionally insignificant

Question 8

Latissimus Dorsi

Answer 8

Adducts, extends, and internally (medially) rotates the glenohumeral joint

Reverse origin: laterally flexes the trunk

If the humerus is fixed to the glenoid fossa of the scapula it can retract depress and downwardly rotate the scapula

Active in resisted depression of the humerus in hip hike

Question 9

Pectoralis Major

Answer 9

Humeral adduction and internal (medial) rotation (*cannot medially rotate without adduction)

In anatomical position the clavicular head flexes the humerus and the sternal head extends the humerus
Both heads horizontally flex the humerus
When the arm is flexed both heads extend it
When the arm is extended both heads flex it

Question 10

Teres Major

Answer 10

Extends, adducts and medially rotates the humerus at the GHJ when the scapula is stabilised

Reversed origin: without scapula stabilised, upwardly rotates the scapula

Question 11

Deltoid

Answer 11

All heads abduct the humerus

Middle head: abducts (strongest head)

Anterior head: medially rotates and flexes the humerus

Posterior head: laterally rotates and extends the humerus

Question 12

Supraspinatus

Answer 12

Abducts the humerus

Stabilizes head of humerus in the glenoid fossa

Question 13

Infraspinatus

Answer 13

External (lateral) rotation and extension of humerus

Stabilizes head of humerus in the glenoid fossa

Question 14

Teres minor

Answer 14

External (lateral) rotation and extension of humerus

Stabilizes head of humerus in the glenoid fossa

Question 15

Subscapularis

Answer 15

Medial rotation of the humerus
May weakly adduct the humerus and weakly flex
Stabilizes head of humerus in the glenoid fossa

Question 16

Coracobrachialis

Answer 16

Weakly flexes and adducts the humerus

Pulls the humerus upwards

Question 17

Long head of triceps brachii

Answer 17

Extends the shoulder
Extends the elbow
*most active in shoulder extension

Question 18

Biceps Brachii

Answer 18

Forearm supination *against resistance, while maintaining extension

Elbow flexion *most active when forearm is supine

Shoulder flexion
Both heads active in resisted shoulder abduction
Short head active is resisted shoulder adduction
Short head sometimes acts during medial rotation of the shoulder