1c - Muscles Involved in Movement of the Arm and Forearm

Question 1

Pectoralis major - Origin, Insertion, Action, and Innervation

Answer 1

Origin: Sternal end of clavicle, sternum, cartilage of ribs 1 - 6, and aponeurosis of external oblique muscle.
Insertion: Greater tubercle of humerus by a short tendon.
Primary action: Prime mover of arm flexion. Rotates arm medially. Adducts the arm.
Other action(s): With scapula fixed, helps pull ribs up (help in climbing, throwing, pushing, and forced inspiration).
Innervation: Lateral and Medial Pectoral

Question 2

Latissimus dorsi - Origin, Insertion, Action, and Innervation

Answer 2

Origin: Indirectly attaches via thoracolumbar fascia into spines of T7 - L5, lower 3 - 4 ribs, and iliac crest.
Insertion: Spirals around Teres Major and inserts into floor of intertubercular sulcus of humerus.
Primary action: Primer mover of arm extension. Adduction and medial rotation of arm.
Innervation: Thoracodorsal

Question 3

Deltoid - Origin, Insertion, Action, and Innervation

Answer 3

Origin: Lateral third of clavicle, acromion and spine of scapula.
Insertion: Deltoid tuberosity of humerus.
Primary action: Prime mover of arm abduction. Antagonistic to Pectoralis Major and Latissimus Dorsi.
Other action(s): Anterior fibers can flex and medially rotate the arm (synergist to Pectoralis Major). Posterior fibers extend and laterally rotate the arm (opposite of anterior fibers).
Innervation: Axillary

Question 4

Teres major - Origin, Insertion, Action, and Innervation

Answer 4

Origin: Posterior surface of scapula at inferior angle.
Insertion: Crest of lesser tubercle on anterior humerus.
Primary action: Extends, medially rotates, and adducts the arm. Synergist of Latissimus dorsi muscle.
Innervation: Lower Subscapular

Question 5

Teres Minor - Origin, Insertion, Action, and Innervation

Answer 5

Origin: Lateral border of posterior scapular surface.
Insertion: Greater tubercle of humerus on posterior surface. Inferior to Infraspinatus muscle insertion.
Primary action: Laterally rotates arm.
Other action(s): Helps hold head of humerus in glenoid cavity (stabilizes joint). These actions are the same as the infraspinatus muscle (may be inseparable).
Innervation: Axillary

Question 6

Supraspinatus - Origin, Insertion, Action, and Innervation

Answer 6

Origin: Supraspinous fossa of the scapula.
Insertion: Superior part of greater tubercle of humerus.
Primary action: Initiates abduction of arm.
Other action(s): Stabilizes shoulder joint and helps prevent downward dislocation of humerus.
Innervation: Suprascapular

Question 7

Infraspinatus - Origin, Insertion, Action, and Innervation

Answer 7

Origin: Infraspinous fossa of the scapula.
Insertion: Greater tubercle of humerus on the posterior surface (behind Supraspinatus muscle insertion).
Primary action: Laterally rotates arm.
Other action(s): Helps hold head of humerus in glenoid cavity (stabilizes joint). These actions are the same as the Teres Minor muscle (may be inseparable).
Innervation: Suprascapular

Question 8

Subscapularis - Origin, Insertion, Action, and Innervation

Answer 8

Origin: Subscapular fossa of scapula.
Insertion: Lesser tubercle of humerus.
Primary action: Medially rotates arm. Assisted by Pectoralis Major muscle.
Other action(s): Helps to hold head of humerus in glenoid cavity (stabilizes joint).
Innervation: Upper and Lower Subscapular

Question 9

Coracobrachialis - Origin, Insertion, Action, and Innervation

Answer 9

Origin: Coracoid process of scapula.
Insertion: Medial surface of humerus shaft.
Primary action: Flexion and adduction of arm. Synergist to Pectoralis Major muscle.
Innervation: Musculocutaneous

Question 10

What is/are the major muscle(s) in arm flexion?

Answer 10

Muscles that originate anteriorly to the shoulder joint.
Primarily the Pectoralis Major muscle. The anterior fibers of the Deltoid muscle and the Coracobrachialis muscle contributes.

Question 11

What is/are the major muscle(s) in arm extension?

Answer 11

Muscles that originate posterior to the shoulder joint. Primarily the Latissimus Dorsi muscle. Also includes the posterior Deltoid muscle fibers and Teres Major muscle.

Question 12

What is/are the major muscle(s) in arm abduction?

Answer 12

Middle region of the Deltoid muscle that extends over the superior and lateral side of the humerus.
Supraspinatus initiates.

Question 13

What is/are the major muscle(s) in arm adduction?

Answer 13

The Pectoralis Major muscle (anteriorly) and Latissimus Dorsi muscle (posteriorly).
Coracobrachialis and Teres Major assists.

Question 14

What is/are the major muscle(s) in arm rotation?

Answer 14

Lateral and medial rotation of the arm are primarily due to rotator cuff muscles (Teres Minor, Infraspinatus, Supraspinatus, and Subscapularis muscle). Latissimus Dorsi, Teres Major, and Pectoralis Major muscles also contribute.

Question 15

Triceps brachii - Origin, Insertion, Action, and Innervation

Answer 15

Origin: Long head [Infraglenoid tubercle of scapula], Lateral head [Posterior shaft of humerus], Medial head [Posterior shard of humerus distal to radial groove]
Insertion: By common tendon into olecranon of ulna.
Primary action: Forearm extension. Antagonist of forearm flexors.
Innervation: Radial

Question 16

Biceps brachii - Origin, Insertion, Action, and Innervation

Answer 16

Origin: Short head [Coracoid process], Long head [Supraglenoid tubercle and lip of glenoid cavity]
Insertion: By common tendon into radial tuberosity.
Primary action: Flexes and supinates forearm.
Other action(s): Weak flexor of arm at the shoulder.
Innervation: Musculocutaneous

Question 17

Brachialis - Origin, Insertion, Action, and Innervation

Answer 17

Origin: Anterior surface of distal humerus near Deltoid muscle insertion.
Insertion: Coronoid process of ulna and capsule of elbow joint.
Primary action: Flexes forearm.
Innervation: Musculocutaneous

Question 18

Brachioradialis - Origin, Insertion, Action, and Innervation

Answer 18

Origin: Lateral supracondylar ridge at distal end of humerus.
Insertion: Base of styloid process of radius.
Primary action: Synergist in forearm flexion.
Other action(s): Stabilizes elbow during rapid flexion and extension.
Innervation: Radial

Question 19

What is/are the major muscle(s) in forearm extension?

Answer 19

Triceps Brachii muscle.

Question 20

What is/are the major muscle(s) in forearm flexion?

Answer 20

In order of decreasing strentgh: Brachialis, biceps brachii, and brachioradialis.
Brachialis and biceps contract together. Bracialis lifts ulna as biceps lift radius.