Pectoralis major muscle Information & Pectoralis major muscle Links at HealthHaven.com

Pectoralis major
	Pectoralis major
Latin	Musculus pectoralis major
Gray's	subject #122 436
Origin	Clavicular head: anterior surface of the medial half of the clavicle.; Sternocostal head: anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle
Insertion	intertubercular groove of the humerus
Artery	pectoral branch of the thoracoacromial trunk
Nerve	lateral pectoral nerve and medial pectoral nerve; Clavicular head: C5 and C6; Sternocostal head: C7, C8 and T1
Actions	Clavicular head: flexes the humerus; Sternocostal head: extends the humerus; As a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.
MeSH	Pectoralis+Muscles

The pectoralis major is a thick, fan-shaped muscle, situated at the chest (anterior) of the body. It makes up the bulk of the chest muscles in the male and lies under the breast in the female. Underneath the pectoralis major is the pectoralis minor, a thin, triangular muscle.

[edit] Origin and insertion

It arises from the anterior surface of the sternal half of the clavicle; from breadth of the half of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib; from the cartilages of all the true ribs, with the exception, frequently, of the first or seventh and from the aponeurosis of the abdominal external oblique muscle.

From this extensive origin the fibers converge toward their insertion; those arising from the clavicle pass obliquely downward and outwards (laterally), and are usually separated from the rest by a slight interval; those from the lower part of the sternum, and the cartilages of the lower true ribs, run upward and laterally, while the middle fibers pass horizontally.

They all end in a flat tendon, about 5 cm in breadth, which is inserted into the lateral lip of the bicipital groove of the humerus.

Electromyography suggests that it consists of at least six groups of muscle fibres that can be independently coordinated by the central nervous system.^[1]

[edit] Laminae

This tendon consists of two laminae, placed one in front of the other, and usually blended together below.

The anterior lamina, which is thicker, receives the clavicular and the uppermost sternal fibers. They are inserted in the same order as that in which they arise: the most lateral of the clavicular fibers are inserted at the upper part of the anterior lamina; the uppermost sternal fibers pass down to the lower part of the lamina which extends as low as the tendon of the Deltoid and joins with it.

The posterior lamina of the tendon receives the attachment of the greater part of the sternal portion and the deep fibers, i. e., those from the costal cartilages.

These deep fibers, and particularly those from the lower costal cartilages, ascend the higher, turning backward successively behind the superficial and upper ones, so that the tendon appears to be twisted.

The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given off which covers the intertubercular groove of the humerus and blends with the capsule of the shoulder-joint.

From the deepest fibers of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia of the arm.

[edit] Variations

The more frequent variations include greater or less extent of attachment to the ribs and sternum, varying size of the abdominal part or its absence, greater or less extent of separation of sternocostal and clavicular parts, fusion of clavicular part with deltoid, and decussation in front of the sternum.

Deficiency or absence of the sternocostal part is not uncommon.

Absence of the clavicular part is less frequent.

Rarely, the whole muscle is missing. This may accompany absence of the breast in females. (See Poland syndrome).

[edit] Actions

The pectoralis major has three actions. It flexes the humerus, as in throwing a ball side-arm, and in lifting a child. It also adducts the humerus, as when flapping arms. It also rotates the humerus medially, as occurs when arm-wrestling.

[edit] Training

The pectoralis muscle can be trained for athletic or bodybuilding purposes^[2]. The following compound exercises are often used to increase the strength and mass of the muscle:

Bench press, with various bench angles (flat, incline, and decline)
Push up
Dips

Isolation exercises include:

Flyes or Flies
Cable Crossovers
"Pec Deck" machines

[edit] References

^ Brown JM, Wickham JB, McAndrew DJ, Huang XF. (2007). Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. J Electromyogr Kinesiol. 17(1):57-73. PMID 16458022 doi:10.1016/j.jelekin.2005.10.007
^ Chest Exercise Menu

[edit] External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

[edit] Notes

[0] Brown JM, Wickham JB, McAndrew DJ, Huang XF. (2007). Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. J Electromyogr Kinesiol. 17(1):57-73. PMID 16458022 doi:10.1016/j.jelekin.2005.10.007

[1] Chest Exercise Menu

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