Origin Insertion Nerve Supply of Pectoralis Major

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Origin Insertion nerve Supply of Pectoralis Major/Pectoralis major is the superior most and largest muscle of the anterior chest wall. It is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla. Its origin lies anterior surface of the medial half of the clavicle, the anterior surface of the sternum, the first 7 costal cartilages, the sternal end of the sixth rib, and the aponeurosis of the external oblique of the anterior abdominal wall. The insertion of the pectoralis major is at the lateral lip of the intertubercular sulcus of the humerus. There are 2 heads of the pectoralis major, the clavicular and the sternocostal, which reference their area of origin. The sternocostal head is described as having between 2 to 7 distinct segments.

Origin Insertion nerve Supply of Pectoralis Major

Structure and Function of Pectoralis Major

The function of the pectoralis major is 3-fold and dependent on which heads of muscles are involved.

  • Flexion, adduction and medial rotation of the arm at the glenohumeral joint
  • Clavicular head causes flexion of the extended arm
  • Sternoclavicular head causes extension of the flexed arm

The pectoralis major shows variation in muscle fiber length, differing from the majority of muscle fibers in the human body, which usually show uniform length. This configuration of the muscle fibers potentially allows for more power production through differing muscle shortening velocities.

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Nerves of Pectoralis Major

The 2 heads of the pectoralis major have different nervous supplies. The clavicular head derives its nerve supply from the lateral pectoral nerve. The medial pectoral nerve innervates the sternocostal head. The lateral pectoral nerve arises directly from the lateral cord of the brachial plexus, and the medial pectoral nerve arises from the medial cord.

Anatomy of the Pectoralis Major

  • Origin – Clavicular head, anterior sternum, costal cartilages 1 to 7, the sternal end rib 6, aponeurosis of the external oblique
  • Insertion – Lateral lip intertubercular sulcus of the humerus
  • Nervous innervation – Medial and lateral pectoral nerves (clavicular head C5, sternocostal head C6/7/8, T1)
  • Function – Flexion, adduction, and medial rotation of the arm at the glenohumeral joint; clavicular head causes flexion of the extended arm; sternoclavicular head causes extension of the flexed arm
  • Arterial supply – Pectoral artery (thoracoacromial trunk, the second branch of the axillary artery)
  • Venous drainage – Pectoral vein (drains into the subclavian vein)


References

Origin Insertion nerve Supply of Pectoralis Major


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