The pectoralis major muscle is the great pectoral muscle. He participates in the motor control of the arm (internal rotation, adduction, anteversion) and as an auxiliary muscle to the breathing. In Poland syndrome, a rare dysplasia, the pectoralis major muscle may be completely absent or underdeveloped.

What is the pectoralis major muscle?

The pectoralis major muscle is the great pectoral muscle. It belongs to the skeletal musculature and participates in the movement of the arm as well as the respiration. The skeletal musculature tensions its fibers towards voluntary effort of its owner (contraction) or relaxes it again (relaxation).

The control and coordination is mainly done by the motor center of the brain; It directs its signals via efferent neural pathways to the muscle, where the motor end plate converts the electrical signal into a biochemical response to which the muscle filaments respond accordingly. Conversely, the brain also receives information from the muscle, such as the degree of tension or strain. This transmission takes place via the afferent nerve tracts. In a healthy person, the large pectoral muscle is strong and visible under the skin.

Anatomy & Construction

The large pectoral muscle is located under the thoracic fascia, which forms part of the trunk fascia and separates the muscle upwards. Under the pectoralis major muscle is the pectoralis minor muscle, ie the small pectoral muscle, which completely disappears under its large counterpart and is also involved in certain arm movements and respiration.

The pectoralis major muscle attaches to the bone of the upper arm and has its origin on the sternum, collarbone and cartilage of the six uppermost ribs. The connection between arm and chest area is particularly well recognized in the armpit, where the large pectoral muscle forms an arc. Its structure is composed of three areas, whose names indicate the position in the pectoralis major muscle: The clavicular part (pars clavicularis) forms the uppermost section, followed by the sternum-rib part (Pars sternocostalis) and abdominal part (Pars abdominalis).

Like all muscles of skeletal muscle, the great pectoral muscle belongs to the striated type. The striated musculature owes its name to the fact that it shows in the cross section under the microscope a clear linear structure, which distinguishes it from the smooth muscle.

Function & Tasks

The pectoralis major muscle has two main functional areas: it is a respiratory aid muscle and is responsible for certain arm movements. When a person turns his or her arm inwards, it tenses the large pectoral muscle to pull the limb inward. This process is also referred to as internal rotation. Anteversion, on the other hand, is a forward movement by which the pectoralis major muscle turns the arm at the shoulder joint. By a third type of tension, the muscle can also be shortened so that the arm is pulled to the body (adduction).

The large pectoral muscle is also part of the breathing aid muscles. Physicians assign it to the inspiratory respiratory support muscles, as it can primarily contribute to inhalation, if the person supports the arms. In contrast to the actual respiratory muscles, the auxiliary respiratory muscles can not independently control the inflow and outflow of air into the lungs, but merely play a supporting role. However, this classification is controversial, as a clear distinction is hardly possible and apply to the intercostal muscles and the diaphragm all other muscles involved in breathing, as respiratory auxiliaries.

Diseases

As part of the Poland syndrome, the pectoralis major muscle on one side is completely absent or parts of the muscle are not formed. Often, the sternum-rib part and the belly part are affected. Poland Syndrome is a congenital malformation whose causes can not be completely explained by medicine.

The dysplasia also affects the mammary gland and the external appearance of the breast. The side of the body on which Poland Syndrome manifests has a smaller nipple with a particularly dark atrium and less fatty tissue compared to the healthy breast, while the other breast may have too much fatty tissue. This additional mass depends not only on the body weight and the total fat content, but is also asymmetrically shifted in Poland syndrome beyond. The thorax and ribs may show deviations in shape, and the small pectoral muscle may also be missing (pectoralis minor muscle).

Other malformations may also appear: fingers may be missing or fused together; The arm may be less powerful or shorter. In rare cases, dysplasia of the lower extremities occurs. The internal organs can affect the kidneys and / or the heart, but the latter is rare. The affected are mostly male and make up 0.01-0.001% of the population. Therapy of the Poland syndrome is not always necessary, often the treatment is limited to an operative approximation of the breasts.

Significantly more often than the Poland syndrome, adhesions of the large pectoral muscle occur with the large dorsal muscle (latissimus dorsi muscle) or the deltoid muscle (deltoid muscle).

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