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Pectoralis Major Muscle – Attachment, Action & Innervation

image descriptionPectoralis Major Muscle

Pectoralis major is a thick, fan-shaped muscle contributing to the thoracobrachial motion. It consists of a clavicular part and a sternal part, both converging to a flat tendon that inserts on the humerus. It’s innervated by both medial and lateral pectoral nerves.

An image showing the Pectoralis Major Muscle (highlighted) attached to the upper limb along with other muscles (Deltoid, Latissimus dorsi, Biceps brachii, Brachioradialis)
An image showing the Pectoralis Major Muscle (highlighted) attached to the upper limb along with other muscles (Deltoid, Latissimus dorsi, Biceps brachii)
An image showing the Pectoralis Major Muscle (highlighted) attached to the upper limb along with other muscles (Coracobrachialis, Biceps brachii)
An image showing the 2 heads of the Pectoralis major muclse (Clavicular and Sternal heads) attached to the upper limb
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image descriptionAttachments of Pectoralis Major Muscle: Origin & Insertion

Origin: (proximal attachments)
a. Clavicular head: medial half of the clavicle.
b. Sternal head: sternum, upper costal cartilages (1-6), and the aponeurosis of the external oblique.

Insertion: (distal attachments)
a. Lateral lip of the intertubercular (bicipital) groove of the humerus.
b. Crest of the greater tubercle of the humerus.

An image showing the Pectoralis Major Muscle (highlighted) attached to the upper limb along with other muscles (Deltoid, Latissimus dorsi, Biceps brachii, Brachioradialis)
An image showing the 2 heads of the Pectoralis major muclse (Clavicular and Sternal heads) attached to the upper limb
An image showing the Origin and Insertion of the Pectoralis major muscle on the upper limb
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Actions of Pectoralis Major Muscle:

Clavicular head:

image descriptionFlex the arm at the shoulder (glenohumeral) joint.

Sternal head:

image descriptionExtends the arm  at the shoulder (glenohumeral) joint from a flexed position.

Both heads working together:

image descriptiona. Medially rotate the arm at the shoulder (glenohumeral) joint.

Arm rotation (medially)
Arm rotation (medially)
Arm rotation (medially)
Arm rotation (medially)
Arm rotation (medially)

image descriptionb. Adduct the arm at the shoulder (glenohumeral) joint.

Innervation of Biceps Brachii:

image descriptionNerves to the muscle:
a. Lateral pectoral nerve to the clavicular head.
b. Medial pectoral nerve to the sternal head.
image descriptionNerve roots:
a. C5, C6, C7 (lateral pectoral nerve to the clavicular head).
b. C8 and T1 (medial pectoral nerve to the sternal head).
An image showing the Lateral and Medial pectoral nerves coming out of the brachial plexus
An image showing the Lateral and Medial pectoral nerves coming out of the brachial plexus
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