Muscles of the Pectoral Region

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Pectoralis Major Muscle:

• Major fan-shaped muscle of ventral body wall.

Lateral border:

• Forms anterior axillary fold.

Superior border:

• Forms one boundary of deltopectoral triangle.

Origin:

• Clavicular head from medial half of clavicle; sternal head from manubrium to lower body.

Insertion:

• Lateral lip of intertubercular groove of humerus.

Innervation:

• Medial and lateral pectoral nerves (from medial and lateral cords of brachial plexus).

Actions:

• Adducts and medially rotates humerus.

• Draws shoulder anteriorly and medially.

• Clavicular head fibers active in flexing humerus.

• Sternal head fibers active in extending humerus from 30 degrees of flexion.

Pectoralis Minor Muscle:

• Deep to pectoralis major; does not connect to humerus.

Origin:

• Outer surfaces of ribs 2-5 near costal cartilages and fascia of associated intercostal spaces.

Insertion:

• Coracoid process of scapula.

Innervation:

• Medial pectoral nerve.

Actions:

• An accessory muscle of respiration when shoulder is in fixed position.

• Stabilizes scapula by drawing it forward, medially and downward.

• If scapula is fixed it elevates the ribs.

Subclavius Muscle:

• Relatively insignificant muscle that protects neurovascular bundle underlying clavicle.

Origin:

• Upper border of first rib and costal cartilage.

Insertion:

• Inferior surface of clavicle.

Innervation:

• Nerve to subclavius (from upper trunk of brachial plexus).

Actions:

• Draws clavicle downward and forward.

Serratus Anterior Muscle:

• Overlies much of lateral thoracic wall.

Origin:

• Outer surfaces of ribs 1-8,9; lateral to pectoralis minor.

Insertion:

• Length of medial border of ventral surface of scapula.

Innervation:

• Long thoracic nerve (from upper trunk of brachial plexus).

Actions:

• Protracts and abducts scapula.

• Holds scapula along posterior thoracic wall.

• Laterally rotates scapula (counterclockwise, from posterior view).

• Elevates arm from horizontal to vertical.

• Damage to the long thoracic nerve will paralyze this muscle, resulting in a condition known as "winged scapula" in which the vertebral border of the scapula is lifted off of the rib cage. The patient will be unable to abduct their arm above the horizontal. The long thoracic nerve is vulnerable during surgical procedures of the chest wall, particularly in radical mastectomies.

More Topics on Chest Wall:

1. Osteology of Pectoral Region
2. Glandular Structure of the Mammary Gland
3. Development of the Breast
4. Fluid Circulation in the Breast
5. Muscles of the Pectoral Region
6. Intercostal Connective Tissue
7. Notes on Neurovascular Bundle

Additional Reading:

Histology and Cytology

1. Cell Components
2. Nervous Tissue
3. Muscle Tissue
4. Lymphoid Tissue
5. Integument
6. Respiratory System
7. Gastrointestinal System
8. Renal/Urinary System
9. Male Reproductive System
10. Female Reproductive System

Gross Anatomy

1. Back and Nervous System
2. Thorax
3. Abdomen, Pelvis, and Perineum
4. Upper Limb
5. Lower Limb
6. Head and Neck
7. Chest Wall
8. Shoulder

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1. Video of HEENT Examination in a Clinical Setting

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