Thorax & Back Muscles Actions

Question 1

Pectoralis major

Answer 1

Flexes arm (PM), adducts arm, medially rotates arm

Question 2

Pectoralis minor

Answer 2

Draws scapula forward and downward when ribs fixed, elevates 3rd-5th ribs during forced expiration when scapula is fixed

Question 3

Serratus anterior

Answer 3

Holds scapula against chest wall, rotates scapula, important to stabilize shoulder for arm movements

Question 4

Deltoid

Answer 4

Abducts arm (PM), anterior fibers flex and medially rotate arm, posterior fibers extend and laterally rotate arm

Question 5

Trapezius

Answer 5

Stabilize scapula, superior fibers elevate scapula and extend head, middle fibers adduct scapula, inferior fibers depress scapula

Question 6

Latissimus dorsi

Answer 6

Extends arm (PM), adducts arm, medially rotates arm, draws arm inferiorly and posteriorly

Question 7

Infraspinatus

Answer 7

Laterally rotates arm, stabilizes shoulder

Question 8

Teres minor

Answer 8

Laterally rotates arm, stabilizes shoulder

Question 9

Teres major

Answer 9

Extends arm, adducts arm, medially rotates arm