Pectoralis Major
The pectoralis major is a large, fan-shaped muscle that covers the upper chest. It has two heads (clavicular and sternocostal) and is a powerful adductor, flexor, and medial rotator of the arm.
Origin, Insertion, Action, Innervation
OOrigin
Clavicular head: Medial half of clavicle. Sternocostal head: Sternum, upper six costal cartilages, and aponeurosis of external oblique.
IInsertion
Lateral lip of intertubercular (bicipital) groove of humerus
AAction
- • Adduction of the arm
- • Medial rotation of the arm
- • Flexion of the arm (clavicular head)
- • Extension from flexed position (sternocostal head)
NInnervation
Medial pectoral nerve (C8, T1) and lateral pectoral nerve (C5, C6, C7)
Blood Supply
Pectoral branches of thoracoacromial artery
Clinical Relevance
Rupture of the pectoralis major can occur during heavy bench pressing or other forceful activities. Poland syndrome involves congenital absence of the pectoralis major. The muscle is used as a flap in breast reconstruction surgery.
Palpation
Easily palpated on the anterior chest wall. Have the patient adduct the arm against resistance to feel the muscle contract. The clavicular and sternocostal heads can be distinguished.
Study Tips
- ✓Two heads = two origins, one insertion (bicipital groove)
- ✓Fibers twist 180° before inserting - lower fibers end up higher
- ✓Two nerves: medial (lower fibers) and lateral (upper fibers)
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Common questions about the pectoralis major
The pectoralis major has two heads. The clavicular head originates from the medial half of the clavicle. The sternocostal head originates from the sternum, upper six costal cartilages, and the aponeurosis of the external oblique muscle.
The pectoralis major is a powerful adductor and medial rotator of the arm. The clavicular head also assists with flexion, while the sternocostal head can assist with extension from a flexed position.
The clavicular head assists with arm flexion and is innervated mainly by the lateral pectoral nerve. The sternocostal head assists with extension from a flexed position and is innervated mainly by the medial pectoral nerve. Both heads work together for adduction and medial rotation.
Poland syndrome is a congenital condition characterized by absence or underdevelopment of the pectoralis major muscle, often with associated chest wall and upper limb abnormalities on the same side.