Pectoralis Major (*Pecs)
Thorax · Trunk
The pectoralis major is the large, fan-shaped muscle that forms the bulk of the anterior chest wall and the anterior fold of the axilla. It has two main heads plus an abdominal slip: a clavicular head from the medial clavicle, a sternocostal head from the sternum and costal cartilages 1 to 6, and an abdominal part from the anterior rectus sheath. All fibres converge to insert on the crest of the greater tubercle of the humerus, along the lateral lip of the intertubercular sulcus. Its overall action is adduction and medial rotation of the arm; the clavicular head flexes the arm, whereas the sternocostal head extends it from a flexed position back toward the side. It is supplied by the lateral and medial pectoral nerves (C5 to T1), named for the cords of the brachial plexus from which they arise rather than their relative position.
Origin, Insertion, Action & Nerve
Origin
Clavicular head: medial clavicle; Sternocostal head: sternum and costal cartilages 1–6; Abdominal part: anterior rectus sheath
Insertion
Crest of the greater tubercle (intertubercular sulcus) of the humerus
Action
Adduction and medial rotation of arm; clavicular head flexes arm; sternocostal head extends arm from flexed position
Nerve
Lateral and medial pectoral nerves (C5–T1)
Attachments explained
The Pectoralis Major (*Pecs) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Clavicular head: medial clavicle; Sternocostal head: sternum and costal cartilages 1–6; Abdominal part: anterior rectus sheath
Insertion
Crest of the greater tubercle (intertubercular sulcus) of the humerus
Action & function
When the Pectoralis Major (*Pecs) contracts, it produces the following movements: Adduction and medial rotation of arm; clavicular head flexes arm; sternocostal head extends arm from flexed position.
As part of the Thorax group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Pectoralis Major (*Pecs) receives its nerve supply from the Lateral and medial pectoral nerves (C5–T1). This nerve carries fibres from spinal segment(s) C5, T1.
Because a muscle can only contract when its nerve is intact, injury to the Lateral and medial pectoral nerves or to its spinal roots (C5, T1) can weaken or paralyse the Pectoralis Major (*Pecs), impairing the movements it normally produces (adduction and medial rotation of arm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Pectoralis Major (*Pecs) (the OIANS method)
Study pectoralis major by its two heads and the opposite jobs they do at the shoulder. The upper clavicular head flexes the arm forward, while the lower sternocostal head pulls a flexed arm back down, so together they can raise and lower the arm through a wide arc, and both unite to adduct and medially rotate it, the classic bear-hug movement.
Use the pectoral nerves as a plexus lesson: the lateral pectoral nerve comes from the lateral cord and the medial pectoral nerve from the medial cord, a naming quirk worth memorising because the medial nerve actually pierces and supplies pectoralis minor before reaching this muscle. Linking the insertion at the lateral lip of the bicipital groove to its neighbours, latissimus dorsi and teres major, also cements the trio of anterior and posterior axillary fold muscles.
Frequently asked questions
Where is the Pectoralis Major (*Pecs) located?
The Pectoralis Major (*Pecs) is a muscle of the Thorax group, located in the Trunk.
What is the origin of the Pectoralis Major (*Pecs)?
Clavicular head: medial clavicle; Sternocostal head: sternum and costal cartilages 1–6; Abdominal part: anterior rectus sheath
What is the insertion of the Pectoralis Major (*Pecs)?
Crest of the greater tubercle (intertubercular sulcus) of the humerus
What movements does the Pectoralis Major (*Pecs) produce?
Adduction and medial rotation of arm; clavicular head flexes arm; sternocostal head extends arm from flexed position
What nerve supplies the Pectoralis Major (*Pecs)?
Lateral and medial pectoral nerves (C5–T1)
Is the Pectoralis Major (*Pecs) free to study in OIANS?
The Pectoralis Major (*Pecs) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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