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The pectoralis muscles are a group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. There are two such muscles on each side of the sternum (breastbone) in the human body: the pectoralis major and the pectoralis minor. The pectoralis major is the largest muscle of the anterior chest wall, lying underneath the breast tissue and forming the anterior wall of the axilla. The pectoralis minor lies underneath the pectoralis major, originating from the middle ribs and inserting into the scapula (shoulder blade). These muscles are responsible for a wide range of motions, including flexion, adduction, and internal rotation of the humerus, as well as stabilising the scapula.
| Characteristics | Values |
|---|---|
| Number of muscles in the pectoral region | 3 |
| Names of the muscles | Pectoralis major, pectoralis minor, serratus anterior |
| Pectoralis major characteristics | Thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla |
| Pectoralis minor characteristics | Lies underneath the pectoralis major, arising from the middle ribs and inserting into the scapula (shoulder blade) |
| Serratus anterior characteristics | Located laterally in the chest wall and forms the medial border of the axilla region |
| Function of the pectoralis major | Adduction, or depression, of the arm (in opposition to the deltoideus muscle) and rotation of the arm forward about the axis of the body |
| Function of the pectoralis minor | Draws the shoulder forward and downward (in opposition to the trapezius muscle) |
| Function of the serratus anterior | Rotates the scapula, allowing the arm to be raised over 90 degrees |
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What You'll Learn
The pectoralis major
The primary functions of the pectoralis major are flexion, adduction, and internal rotation of the humerus. The muscle is responsible for keeping the arm attached to the trunk of the body. The clavicular part of the muscle contributes to flexion, horizontal adduction, and inward rotation of the humerus, while the sternocostal part contributes to downward and forward movement of the arm, as well as inward rotation during adduction. The pectoralis major also assists in breathing by aiding in deep or forced inspiration.
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The pectoralis minor
Dysfunction of the pectoralis minor can result in pain and restricted movement in the neck and upper back, as well as an increased risk of rotator cuff issues. Shortening of the pectoralis minor can impinge on the brachial plexus and axillary blood vessels, leading to shoulder impingement and thoracic outlet syndrome. Absence of the pectoralis minor is rare but can occur in certain diseases such as Poland syndrome.
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The serratus anterior
The vascular supply to the serratus anterior comes from the superior and lateral thoracic arteries (branches of the axillary artery) as well as branches from the thoracodorsal artery (a branch of the subscapular artery). The innervation is supplied by the long thoracic nerve, a branch of the brachial plexus.
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The subclavius
The arterial supply to the subclavius muscle is provided by the clavicular branch of the thoracoacromial artery, with contributions from the suprascapular artery. The muscle receives blood from the clavicular branch, ensuring the necessary oxygenation and nutrient supply for its function.
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The chest wall and shoulder
The pectoralis muscles are a group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. They are responsible for a wide range of movements in the upper extremities, including flexion, adduction, and internal rotation of the humerus, as well as stabilisation of the scapula.
The pectoralis major is the largest muscle of the anterior chest wall. It is thick and fan-shaped, lying underneath the breast tissue and forming the anterior wall of the axilla. Its origin lies on the 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 pectoralis major has two heads: the clavicular and the sternocostal. These reference their area of origin and can be tested separately. The clavicular head can be tested by transversely adducting the arm at the glenohumeral joint against resistance, while the sternocostal head can be tested by adducting the arm at the glenohumeral joint.
The pectoralis minor lies underneath the pectoralis major, arising from the middle ribs (specifically the 3rd to 5th ribs) and inserting into the scapula (shoulder blade). It aids in drawing the shoulder forward and downward and plays a role in stabilising the scapula by drawing it anteroinferiorly against the thoracic wall.
Other muscles in the pectoral region include the serratus anterior and the subclavius. The serratus anterior is located laterally in the chest wall and forms the medial border of the axilla. It consists of several strips that originate from the lateral aspects of ribs 1-8 and attach to the costal surface of the medial border of the scapula. The subclavius is a small muscle located directly underneath the clavicle, running horizontally. It provides minor protection to the underlying neurovascular structures.
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Frequently asked questions
The pec muscles are located on the anterior chest wall.
The pec muscles are the group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls.
Yes, there are two types of pec muscles: the pectoralis major and the pectoralis minor.
The pectoralis major is the superior most and largest muscle of the anterior chest wall. It lies underneath the breast tissue and forms the anterior wall of the axilla.
The pectoralis minor lies underneath the pectoralis major, arising from the middle ribs and inserting into the scapula (shoulder blade).
