Dominic Stone
The pectineus muscle is a flat, quadrangular muscle located in the superomedial part of the anterior thigh. It is the most anterior (closest to the front) of the hip adductors. The muscle's primary action is hip flexion, and it also assists in hip adduction and external rotation of the hip. The pectineus is considered a transitional muscle between the anterior thigh and medial thigh due to its innervation by the femoral nerve and, occasionally, the obturator nerve. The muscle originates from the pectineal line of the pubis and extends to the area below the lesser trochanter of the femur.
| Characteristics | Values |
|---|---|
| Number of muscles in the pectoral region | 3 |
| Names of the muscles | Pectoralis major, pectoralis minor, serratus anterior |
| Location | Anterior chest wall |
| Function | Connects the front walls of the chest with the bones of the upper arm and shoulder |
| Number of muscles on each side of the sternum | 2 |
| Muscle that constitutes the bulk of the chest muscles | Pectoralis major |
| Shape of the pectoralis major | Thick, fan-shaped |
| Location of the pectoralis minor | Underneath the pectoralis major |
| Function of the pectoralis minor | Stabilises the scapula by drawing it anteroinferiorly against the thoracic wall |
| 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 muscle is a prominent chest muscle
The clavicular part originates from the anterior surface of the medial half of the clavicle, while the sternocostal part originates from the anterior surface of the sternum and the anterior aspects of the costal cartilages of ribs 1-6. The abdominal part is the smallest and originates from the anterior layer of the rectus sheath. The muscle fibres from all three parts run laterally, converging towards the proximal humerus and giving off a broad tendon that inserts along the lateral lip of the intertubercular sulcus of the humerus.
The pectoralis major is responsible for the flexion, adduction, and internal rotation of the humerus at the shoulder joint. The clavicular portion of the muscle flexes the humerus up to 90 degrees in a horizontal plane, while the sternocostal portion can produce the antagonistic movement and extend the humerus back to the anatomical position. Acting together with the latissimus dorsi muscle, the pectoralis major pulls the trunk forwards or upwards when its humeral attachment is fixed, which is important in activities such as climbing.
The pectoralis major muscle is also associated with Poland Syndrome, a rare congenital condition in which the whole muscle is missing, usually on one side of the body. This condition may also be accompanied by the absence of the breast in females.
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The pectoralis minor muscle lies beneath the pectoralis major
The pectoralis minor muscle is one of the most superficial muscles on the anterior aspect of the chest or thoracic wall. It is located underneath the pectoralis major muscle, which constitutes the bulk of the chest muscles. The pectoralis minor muscle arises as three separate heads from the anterior surface of the 3rd, 4th, and 5th ribs near the corresponding costal cartilages. It extends superolaterally to form a flat tendon, which inserts into the medial border and coracoid process of the scapula.
The pectoralis minor muscle plays an important role in the movement of the scapula. Together with the serratus anterior, it acts in protraction of the scapula, pulling it laterally and anteriorly against the ribcage. This movement is crucial for reaching the arm forward. When the scapula is fixed, the pectoralis minor can function as an accessory muscle of respiration, assisting in deep and forced inspiration by helping to raise ribs 3-5.
The primary nerve supply to the pectoralis minor muscle comes from the medial pectoral nerve (C8, T1), a minor branch of the brachial plexus originating from the cervical portion of the spinal cord. Additionally, the pectoralis minor receives innervation from the lateral pectoral nerve through the 'ansa pectoralis', resulting in spinal root innervation from C5-T1. The vascular supply to the pectoralis minor is provided by several sources, including the thoracoacromial artery and the superior thoracic artery.
The pectoralis minor muscle is clinically significant and serves as a surgical landmark due to the structures located beneath it. It lies deep to the pectoralis major and is covered by a connective tissue layer called the clavicopectoral fascia. Together, these muscles form the anterior wall of the axilla region. Posteriorly, the pectoralis minor is related to the serratus anterior, intercostal muscles, ribs, and several neurovascular and lymphatic structures.
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The pectoralis muscle connects the chest with the upper arm and shoulder
The pectoralis major is the largest and most superior muscle of the anterior chest wall. It is thick and fan-shaped, lying underneath the breast tissue. The pectoralis major constitutes the bulk of the chest muscles. It originates from multiple places along the medial and superior chest, including the anterior sternum, clavicular head, sternal end of rib 6, superior six costal cartilages, and the aponeurosis of the external oblique. All the fibres converge and end in a flat tendon, inserting into the lateral lip of the bicipital groove of the humerus. The pectoralis major is active in deep or forced inspiration, but not expiration. It is responsible for moving the upper extremities in a wide range of motions, including flexion, adduction, and internal rotation of the humerus, as well as stabilising the scapula.
The pectoralis minor lies underneath the pectoralis major, arising from the middle ribs (specifically the 3rd to 5th ribs) and inserting into the coracoid process of the scapula (shoulder blade). It aids in drawing the shoulder forward and downward. The pectoralis minor also helps to stabilise the scapula by drawing it anteroinferiorly against the thoracic wall.
The pectoralis muscles can be strengthened through various exercises, such as the flat barbell bench press and the flat dumbbell bench press. These exercises involve lying supine on a bench with feet flat on the ground and utilising the pectoralis major muscle to lift and lower weights.
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Poland syndrome involves a defect of the pectoralis major muscle
The pectoralis major is a large, fan-like muscle that covers most of the upper, front part of the chest. It constitutes the bulk of the chest muscles, lying underneath the breast. It is thick and fan-shaped, originating from multiple places along the medial and superior chest, including the breastbone (sternum), collarbone (clavicle), and cartilages of the second to the sixth ribs. The pectoralis minor is a thin, triangular muscle that lies underneath the pectoralis major. Both muscles form part of the anterior wall of the axilla region.
Poland syndrome is a congenital unilateral deficiency in the pectoralis major muscle. It is characterised by an underdeveloped chest muscle and, in some cases, short webbed fingers on one side of the body. In most affected individuals, there is an absence of the sternal portion of the pectoralis major, causing the chest to appear concave. The abnormality in the pectoralis major muscle may also result in the absence or underdevelopment of the pectoralis minor. In females, Poland syndrome may cause the underdevelopment or absence of one breast and underlying tissues.
Poland syndrome affects males more commonly than females and most frequently involves the right side of the body. It affects about 1 in 20,000 newborns, and males are affected twice to three times as often as females. The cause of Poland syndrome is unknown, but researchers have suggested that it may result from a disruption of blood flow during embryonic development. There is also evidence of a genetic component, with a study from 2016 showing that a gene on Chromosome 6 is implicated.
Treatment of Poland syndrome depends on its severity and may include surgical correction. In severe cases, an implant can replace the pectoralis major muscle, enabling the thorax to be symmetrical and, in women, the breast as well.
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The pectoralis major muscle is fan-shaped
The pectoralis major is a thick, 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, lying underneath the breast. The pectoralis major constitutes the chest muscles and is the most superficial muscle in the pectoral region. The pectoralis minor lies underneath the pectoralis major.
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 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. All three parts of the muscle converge laterally and insert onto the greater tubercle of the humerus.
The pectoralis major 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's primary functions are flexion, adduction, and internal rotation of the humerus. The clavicular part of the muscle contributes to flexion, horizontal adduction, and inward rotation of the humerus. The sternocostal part contributes to downward and forward movement of the arm and inward rotation when accompanied by adduction.
The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. The muscle acts mainly on the shoulder joint. When 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. When acting together with the latissimus dorsi muscle, the pectoralis major pulls the trunk forwards or upwards when its humeral attachment is fixed.
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Frequently asked questions
The pec muscles, short for pectoralis muscles, are a group of skeletal muscles that connect 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 (breastbone) in the human body: the pectoralis major and the pectoralis minor.
The pectoralis major muscles are located on the anterior surface of the thoracic cage. They are thick, fan-shaped muscles that constitute the bulk of the chest muscles, lying underneath the breast.
The pectoralis minor muscles lie mostly beneath the pectoralis major muscles, arising from the middle ribs and inserting into the scapula (shoulder blade).
The pectoralis muscles are responsible for a wide range of motions, including flexion, adduction, and internal rotation of the humerus, stabilization of the scapula, and elevating and depressing the bones of the thorax.
