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The pectoralis muscle is a fan-shaped muscle that connects the front walls of the chest with the bones of the upper arm and shoulder. There are two pectoralis muscles on each side of the sternum: the pectoralis major and the pectoralis minor. 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 has two heads: the clavicular and sternocostal head. The pectoralis minor is much thinner and triangular in shape and resides below the pectoralis major.
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What You'll Learn
- The pectoralis major is a fan-shaped muscle with three parts
- The muscle is located on the anterior chest wall
- It has two heads: the clavicular and sternocostal head
- The pectoralis major is the superior most and largest muscle of the anterior chest wall
- Poland syndrome is a congenital anomaly characterised by the absence of the pectoralis major
The pectoralis major is a fan-shaped muscle with three parts
The pectoralis major is a fan-shaped muscle that makes up the bulk of the chest muscles. It 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 major is the most superficial muscle in the pectoral region.
The pectoralis major has a broad origin, and based on this, 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 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 clavicular part originates from the anterior surface of the medial half of the clavicle. It is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110-degree angle, it contributes to adduction of the humerus. The clavicular part helps to flex the extended arm up to 90 degrees.
The sternocostal part is the larger of the two heads and 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. It is antagonistic to the clavicular part, contributing to the downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternocostal part facilitates the extension of the flexed arm by pulling it downwards.
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The muscle is located on the anterior chest wall
The pectoralis muscle is a group of skeletal muscles that connect the front walls of the chest to the bones of the upper arm and shoulder. The pectoralis major and the pectoralis minor are the two such muscles found on each side of the sternum (breastbone) in the human body. The pectoralis major is the superior-most and largest muscle of the anterior chest wall. It is thick and fan-shaped, lying underneath the breast tissue. It is also the most superficial muscle in the pectoral region. The pectoralis minor lies underneath its larger counterpart, the pectoralis major. Both muscles form part of the anterior wall of the axilla region.
The pectoralis major has two heads: the clavicular and the sternocostal, which reference their area of origin. The clavicular head originates from the anterior surface of the medial half of the clavicle. The sternocostal head, the larger of the two, 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 upper and lower fibres of the pectoralis major insert into the crest of the greater tubercle of the humerus. The fibres attaching to the clavicular head allow for the flexion of the humerus, as seen when lifting a glass in a toast. The muscle fibres attaching to the sternocostal head permit the horizontal and vertical adduction, extension, and internal rotation of the upper extremity.
The pectoralis minor originates from the third to fifth ribs adjacent to the costochondral junction. The fibres pass upward and laterally to insert into the medial border and superior surface of the coracoid process. It is crucial in stabilising the scapula by pulling it downward and anteriorly against the thoracic wall. The pectoralis minor is also considered a target of interest in patients suffering from neurological issues.
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It has two heads: the clavicular and sternocostal head
The pectoralis muscle is any of the muscles that connect the front walls of the 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 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 has two heads: the clavicular and sternocostal head. The clavicular head originates from the anterior surface of the medial half of the clavicle. The sternocostal head is the larger of the two heads and originates from the anterior surface 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 clavicular head of the pectoralis major can be tested by transversely adducting the arm at the glenohumeral joint against resistance, during which it can be seen and palpated. The sternocostal head can be tested by adducting the arm at the glenohumeral joint against resistance, during which it can also be seen and palpated. The clavicular part of the pectoralis major is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110-degree angle, it contributes to adduction of the humerus.
The sternocostal part is antagonistic to the clavicular part, contributing to the downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibers can also contribute to extension, but not beyond the anatomical position. The pectoralis major acts as a strong adductor and internal rotator of the humerus at the shoulder joint. Acting independently, the clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane. The sternocostal portion of the muscle can produce the antagonistic movement and extend the humerus back to the anatomical position.
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The pectoralis major is the superior most and largest muscle of the anterior chest wall
The pectoralis major arises from parts of the clavicle and sternum, costal cartilages of the true ribs, and the aponeurosis of the abdominal external oblique muscle. It is composed of two heads, the clavicular and the sternocostal, which reference their area of origin. The clavicular head originates from the anterior surface of the medial half of the clavicle. The sternocostal head, which is larger than the clavicular head, 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 two heads of the pectoralis major have different functions and nervous supplies. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part is antagonistic to the clavicular part, contributing to the downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibers can also contribute to extension, but not beyond the anatomical position. The clavicular head derives its nerve supply from the lateral pectoral nerve, while the medial pectoral nerve innervates the sternocostal head.
The pectoralis major is responsible for keeping the arm attached to the trunk of the body. It is active in deep or forced inspiration, but not expiration. When the diaphragm and intercostal muscles are insufficient for proper breathing, the pectoralis major can assist in inspiration. The muscle is also involved in pressing motions, such as bench pressing, which can lead to a rare shoulder injury called pectoralis major tendon rupture.
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Poland syndrome is a congenital anomaly characterised by the absence of the pectoralis major
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. It is the most superficial muscle in the pectoral region.
Poland syndrome is a rare congenital anomaly characterised by the absence of the pectoralis major, usually on one side of the body. It was first described by Alfred Poland in 1840. The pectoralis major muscle may be completely absent in Poland syndrome, or it may be hypoplastic, meaning that it is underdeveloped or smaller than normal. This condition can also result in the absence of the breast in females and can affect other muscles in the region, such as the pectoralis minor, which lies beneath the pectoralis major.
The pectoralis major has two heads, or parts, that are responsible for different actions: the clavicular and the sternocostal. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part is antagonistic to the clavicular part, contributing to the downward and forward movement of the arm and inward rotation when accompanied by adduction.
Poland syndrome often presents with associated abnormalities of the ribs, ranging from hypoplasia to the complete absence of ribs. Syndactyly, or webbed fingers, is also a common feature of Poland syndrome, although it was not present in all cases. In some instances, Poland syndrome may co-occur with other conditions, such as Möbius syndrome, which affects the facial nerves and muscles.
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Frequently asked questions
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 has three parts that originate from three different sites: the clavicular part, the sternocostal part, and the abdominal part.
The pectoralis major is responsible for flexion, adduction, and internal rotation of the humerus. It also keeps the arm attached to the trunk of the body.
