Muscles Acting on the Humerus

Question 1

Biceps Brachii

Answer 1

Act: Flexion and abduction
O: Long head: supraglenoid tuberosity of scapula
Short head: coracoid process of scapula
I: Radial tuberosity and aponeurosis
Innervation: Musculocutaneous

Question 2

Coracobrachialis

Answer 2

Act: Flexion and adduction
O: Coracoid Process
I: Medial shaft of humerus, adjacent to deltoid tuberosity
Innervation: Musculocutaneous

Question 3

Deltoid (anterior one-third)

Answer 3

Act: Flexion, abduction, horizontal adduction, internal rotation
O: Lateral one-third of the clavicle
I: Deltoid tuberosity
Innervation: Axillary

Question 4

Deltoid (middle one-third)

Answer 4

Act: Abduction and flexion
O: Acromion process
I: Deltoid tuberosity
Innervation: Axillary

Question 5

Deltoid (posterior one-third)

Answer 5

Act: Extension, horizontal abduction, abduction, external rotation
O: Spine of the scapula
I: Deltoid tuberosity
Innervation: Axillary

Question 6

Infraspinatus

Answer 6

Act: External rotation, horizontal abduction, humeral head stabilization
O: Infraspinous fossa of scapula
I: Lateral portion of the greater tuberosity of the humerus and GH joint capsule
Innervation: Subscapular

Question 7

Latissimus Dorsi

Answer 7

Act: Extension, internal rotation, adduction, depression of shoulder girdle
O: Spinous process of T6-T12 and the lumbar vertebrae via the lumbodorsal fascia and posterior iliac crest
I: Floor of bicipital groove of the humerus
Innervation: Thoracodorsal

Question 8

Pectoralis Major

Answer 8

Act: Adduction, horizontal adduction, humeral flexion (clavicular segment), internal rotation, and depression of shoulder girdle (clavicular fiber)
O: Medial one-half of the clavicle, anterolateral portion of the sternum, and costal cartilages of ribs 6-7
I: Greater tuberosity of the humerus
Innervation: Lateral and medial pectoral

Question 9

Subscapularis

Answer 9

Act: Internal rotation and humeral head stabilization
O: Anterior surface (subscapular fossa) and axillary border of the scapula
I: Lesser tuberosity of the humerus and ventral portion of the GH capsule
Innervation: Upper and lower subscapular

Question 10

Supraspinatus

Answer 10

Act: Abduction, external rotation, and humeral head stabilization
O: Supraspinous fossa (medial two-thirds) of the scapula
I: Medial aspect of the greater tuberosity and GH joint capsule
Innervation: Subscapular

Question 11

Teres Major

Answer 11

Act: Extension, internal rotation, adduction
O: Inferior angle of scapula and lower one-third of the axillary border of the scapula
I: Medial lip of the bicipital groove
Innervation: Lower subscapular

Question 12

Teres Minor

Answer 12

Act: External rotation and horizontal abduction
O: Lateral upper two-thirds of axillary border of the scapula
I: Lateral aspect of the greater tuberosity
Innervation: Axillary

Question 13

Triceps Brachii

Answer 13

Act: Extension (long head) and adduction
O: Long head: infraglenoid tuberosity of scapula
Lateral head: Lateral and posterior surface of the proximal one-half of the humerus
Medial head: Distal two-thirds of medial and posterior humerus
I: Olecranon process of ulna
Innervation: Radial