Pectoralis Major -The ARM MOVERS

The Pectoralis major is a muscle of the pectoral region. This muscle along with the Pectoralis minor, Subclavius and Serratus anterior forms the pectoral region. It is the largest muscle in this region. Morphologically it is thin and fan-shaped. It is characterized by 2 heads, the large Sternocostal head, and the small Clavicular head.

ORIGIN

The Sternocostal head arises from-

Medial parts of 2nd-6th costal cartilages and aponeurosis of the external oblique muscle of the abdomen.
Lateral half of the anterior surface of the sternum up to 6th costal cartilage.

The Clavicular head arises from the medial half of the anterior aspect of the clavicle.

INSERTION

Pectoralis major is inserted by a bilaminar tendon on the lateral lip of the bicipital groove of the humerus. This tendon has an anterior lamina and a posterior lamina.

Anterior lamina is thick, short and is formed by clavicular fibers.
Posterior lamina is thin, long and is formed by sternocostal and aponeurotic fibers.

NERVE SUPPLY

Pectoralis major is supplied by medial (C8 and T1) and lateral pectoral (C5-C7) nerves.

Important fact-The Pectoralis major and Pectoralis minor are the only muscles of the upper limb which are supplied by all 5 spinal segments that form the Brachial plexus.

BLOOD SUPPLY

The Pectoralis major is supplied by the pectoral branch of the Thoracoacromial trunk which is a branch of the second part of the axillary nerve.

ACTIONS

The Clavicular head is responsible for flexing the arm.
The Sternocostal head is involved in adduction and medial rotation of the arm.

CLINICAL ANATOMY

Poland syndrome involves malfunction of the chest which is caused due to the absence of a Pectoralis major on one side.
Congenital anomaly of a part of the Pectoralis major causes difficulty in adduction and medial rotation of the arm.

CLINICAL TESTING
While lifting a heavy load the clavicular head becomes prominent and while depressing the load the Sternocostal head becomes prominent.

-By Varsha Joshi

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