M01.03.017 Pectoral Region

The pectoral region is located on the anterior chest wall and consists of four key muscles: pectoralis major, pectoralis minor, serratus anterior, and subclavius. These muscles play important roles in the movement and stabilization of the upper limb and the shoulder girdle. This article covers the anatomy, attachments, functions, and innervations of these muscles.

Muscles of the Pectoral Region

1. Pectoralis Major

The pectoralis major is the most superficial muscle in the pectoral region. It is large, fan-shaped, and consists of two heads: clavicular and sternocostal.

Attachments:

• Clavicular head: Originates from the anterior surface of the medial clavicle.
• Sternocostal head: Originates from the anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle.
• Distal attachment: Both heads insert into the intertubercular sulcus of the humerus.

Function:

• Adducts and medially rotates the upper limb.
• Draws the scapula anteroinferiorly.
• The clavicular head flexes the upper limb.

Innervation:

• Lateral and medial pectoral nerves.

2. Pectoralis Minor

The pectoralis minor lies beneath the pectoralis major and contributes to the anterior wall of the axilla.

Attachments:

• Origin: 3rd to 5th ribs.
• Insertion: Coracoid process of the scapula.

Function:

• Stabilizes the scapula by drawing it anteroinferiorly against the thoracic wall.

Innervation:

• Medial pectoral nerve.

3. Serratus Anterior

The serratus anterior is located laterally and forms the medial border of the axilla region.

Attachments:

• Origin: Lateral aspects of ribs 1-8.
• Insertion: Costal (rib-facing) surface of the medial border of the scapula.

Function:

• Rotates the scapula, allowing the arm to be raised above 90 degrees.
• Protracts the scapula, holding it against the ribcage.

Innervation:

• Long thoracic nerve.

4. Subclavius

The subclavius is a small muscle located directly underneath the clavicle. It helps protect neurovascular structures in the area, especially in cases of trauma.

Attachments:

• Origin: Junction of the 1st rib and its costal cartilage.
• Insertion: Inferior surface of the middle third of the clavicle.

Function:

• Anchors and depresses the clavicle.

Innervation:

• Nerve to subclavius.

Table: Summary of Muscle Attachments, Functions, and Innervations

Clinical Relevance: Winging of the Scapula

• Winging of the scapula occurs when the serratus anterior is paralyzed, typically due to damage to the long thoracic nerve. The muscle is responsible for holding the scapula against the ribcage; when it is damaged, the scapula protrudes outward, resembling a “winged” appearance.
• Common causes: Traction injuries, where the upper limb is stretched violently (e.g., in sports or accidents), can result in long thoracic nerve palsy.

Points to Remember:

• The pectoralis major is the largest and most superficial muscle, playing a key role in upper limb movement.
• Pectoralis minor functions to stabilize the scapula, and its paralysis may impair scapular motion.
• The serratus anterior is crucial for scapular rotation and arm elevation beyond 90 degrees.
• The subclavius provides minor protection to neurovascular structures beneath the clavicle.
• Damage to the long thoracic nerve leads to winging of the scapula, impairing scapular stability and movement.