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The pectoral muscles, commonly referred to as pecs, are a group of skeletal muscles that connect the front of the human chest with the bones of the upper arm and shoulder. 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 larger and more superficial of the two, extending across the upper part of the chest and attaching to a ridge at the rear of the humerus (upper arm bone). The pectoralis minor lies underneath the pectoralis major, originating from the middle ribs and attaching to the scapula (shoulder blade).
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What You'll Learn
- The pectoralis major is the largest muscle in the pectoral region
- The pectoralis minor is located beneath the pectoralis major
- The pectoralis muscles connect the chest to the upper arm and shoulder
- The pectoralis major is divided into three parts
- The pectoralis major is vascularized by the pectoral branches of the thoracoacromial artery
The pectoralis major is the largest muscle in the pectoral region
The pectoralis major has two heads: the clavicular and the sternocostal. The clavicular head originates from the anterior surface of the medial half of the clavicle (collarbone). The sternocostal head, which is larger, originates from the anterior surface of the manubrium and body of the sternum, the anterior surface of the superior six costal cartilages, and the superior part of the aponeurosis of the external oblique muscle.
The pectoralis major is a superficial muscle located on the anterior surface of the thoracic cage. It is divided into three parts: the clavicular part, the sternocostal part, and the abdominal part. All three parts converge laterally and insert onto the greater tubercle of the humerus. The main function of this muscle is the adduction and internal rotation of the arm at the shoulder joint.
The clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane. The sternocostal portion produces the antagonistic movement, extending the humerus back to the anatomical position. When the humeral attachment is fixed, the pectoralis major acts in conjunction with the latissimus dorsi muscle to pull the trunk forwards or upwards. This action is important in activities such as climbing.
The pectoralis minor is the smaller and thinner counterpart to the pectoralis major, residing below it. It originates from the third to fifth ribs and inserts into the coracoid process of the scapula. It is crucial in stabilising the scapula by pulling it downward and anteriorly against the thoracic wall.
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The pectoralis minor is located beneath the pectoralis major
The pectoralis minor is crucial in stabilizing the scapula by pulling it downward and anteriorly against the thoracic wall. It also aids in drawing the shoulder forward and downward. When the scapula is stabilized, the pectoralis minor acts as an accessory muscle of inspiration. The pectoralis minor also creates a passage between the ribs for the transit of the brachial plexus, the subclavian artery, and vein.
The pectoralis minor is triangular in shape, while the pectoralis major is thick and fan-shaped. The pectoralis major constitutes the bulk of the chest muscles, lying underneath the breast. It originates from the clavicle, sternum, ribs, and a tendinous extension of the external oblique abdominal muscle. The pectoralis major extends across the upper part of the chest and is attached to a ridge at the rear of the humerus. Its major actions include adduction or depression of the arm and rotation of the arm forward about the axis of the body.
The pectoralis minor and pectoralis major muscles form the anterior wall of the axilla region. The medial and lateral pectoral nerves penetrate the pectoralis minor muscle to innervate it. The vascular supply to the pectoralis minor comes from several sources, including the thoracoacromial artery, superior thoracic artery, and lateral thoracic artery.
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The pectoralis muscles connect the chest to the upper arm and shoulder
The pectoralis muscles are a group of skeletal muscles that connect the chest to the upper arm and shoulder. They are responsible for a wide range of motions in the upper extremities, including flexion, adduction, and internal rotation of the humerus, as well as stabilization of the scapula. There are two pectoralis muscles on each side of the sternum (breastbone): the pectoralis major and the pectoralis minor.
The pectoralis major is the larger and more superficial of the two muscles, constituting the bulk of the chest muscles. It is a thick, fan-shaped muscle that originates from multiple places along the medial and superior chest, including the clavicle, sternum, ribs, and a tendinous extension of the external oblique abdominal muscle. It extends across the upper part of the chest and is attached to a ridge at the rear of the humerus, the long bone of the upper arm. The pectoralis major is responsible for the adduction, or depression, of the arm, as well as the rotation of the arm forward about the axis of the body. It also assists in pulling the trunk up when climbing.
The pectoralis minor is a thin, triangular muscle located beneath the pectoralis major. It originates from the middle ribs and inserts into the scapula (shoulder blade). It aids in drawing the shoulder forward and downward and plays a crucial role in stabilizing the scapula by pulling it downward and anteriorly against the thoracic wall.
The pectoralis muscles work together with other muscles in the region, such as the serratus anterior and the subclavius, to provide a wide range of motion and stability to the upper extremities. The pectoralis major, in particular, is the most superficial muscle in the pectoral region and is active in deep or forced inspiration, assisting in breathing.
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The pectoralis major is divided into three parts
The pectoralis major is the superior-most and largest muscle of the anterior chest wall. It is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla. The pectoralis major is also referred to as the “pecs” or “chest muscle”. It is the most superficial muscle in the pectoral region.
The pectoralis major has a broad origin and is divided into three parts: the clavicular part, the sternocostal part, and the abdominal part. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part contributes to the downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibres can also contribute to extension, but not beyond anatomical position.
The muscle fibres from all three parts run laterally, converging towards the proximal humerus. They give off a broad tendon that inserts along the lateral lip of the intertubercular sulcus of the humerus. The pectoralis major muscle is active in deep or forced inspiration, but not expiration. It is also responsible for keeping the arm attached to the trunk of the body.
The pectoralis major constitutes the bulk of the chest muscles, and its main function is the adduction and internal rotation of the arm in the shoulder joint. The actions of the pectoralis major are dependent on which parts of the muscle are activated. For example, the fibres attaching to the clavicular head allow for the flexion of the humerus, while the muscle fibres attaching to the sternocostal head permit the horizontal and vertical adduction, extension, and internal rotation of the upper extremity.
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The pectoralis major is vascularized by the pectoral branches of the thoracoacromial artery
The pectoralis major is a thick, fan-shaped muscle that constitutes the bulk of the chest muscles, lying underneath the breast. It is a paired, superficial muscle located on the anterior surface of the thoracic cage. It originates at the clavicle, the sternum, the ribs, and a tendinous extension of the external oblique abdominal muscle. The pectoralis major extends across the upper part of the chest and is attached to a ridge at the rear of the humerus. Its primary actions are adduction, or depression, of the arm and rotation of the arm forward about the axis of the body.
The pectoral branch of the thoracoacromial artery is the largest branch and plays a crucial role in vascularizing the pectoralis major. It arises from the thoracoacromial artery as it travels around the medial border of the pectoralis minor muscle and pierces the clavipectoral fascia. The branch then descends between the pectoralis major and minor muscles. In addition to supplying the pectoralis major, the pectoral branch also provides vascularization to the pectoralis minor muscle, the mammary gland, and the skin in the pectoral region.
The vascularization of the pectoralis major by the pectoral branches of the thoracoacromial artery is essential for maintaining the health and function of this muscle. Adequate blood flow ensures that the muscle receives the necessary oxygen and nutrients for its metabolic needs. Furthermore, the vascular supply contributes to the muscle's ability to repair and regenerate in cases of injury or surgical procedures.
The pectoralis major is a highly vascular muscle, and this extensive vascularity has clinical implications. For example, in cases of Poland syndrome, which is an embryonic malformation of the thoracic wall, the pectoralis major may be partially or completely missing. Plastic-surgical reconstruction using the pectoralis major flap has been successfully employed to address this condition. The high vascularity of the pectoralis major flap reduces the incidence of necrosis, making it a reliable option for reconstructive surgery.
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Frequently asked questions
The pectoralis major is a thick, fan-shaped muscle that lies underneath the breast tissue and forms the anterior wall of the axilla. It is the superior most and largest muscle of the anterior chest wall.
The pectoralis minor is a thin, triangular muscle located beneath the pectoralis major. It attaches to the ribs and serves to stabilise the scapula, the large bone of the shoulder.
The serratus anterior is located more laterally in the chest wall and forms the medial border of the axilla region. It originates from the outer surface of the first to eighth ribs and attaches to the costal aspect of the medial margin of the scapula.
The subclavius is a small muscle located directly underneath the clavicle, running horizontally.
