Victor Forge
The breasts are paired structures located on the anterior thoracic wall, in the pectoral region, and are present in both males and females. The base of the breast lies on the pectoral fascia, a flat sheet of connective tissue associated with the pectoralis major muscle. This muscle is one of the large muscles of the chest and is divided into three levels based on how close the axillary lymph nodes are to it. The pectoralis major muscle is connected to the breasts via suspensory ligaments, which attach to the pectoral fascia.
| Characteristics | Values |
|---|---|
| Muscle fibres | When contracted, the nipple becomes erect or pointed outward |
| Connective tissue | The retromammary space is a layer of loose connective tissue between the breast and pectoral fascia |
| Muscle connection | Muscles connect breasts to ribs |
| Pectoral fascia | The base of the breast lies on the pectoral fascia, a flat sheet of connective tissue associated with the pectoralis major muscle |
| Nerve branches | The breast is innervated by the anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves |
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What You'll Learn
The pectoralis major muscle
The pectoralis major is a thick, fan-shaped or triangular convergent muscle that makes up the bulk of the chest muscles and lies under the breast. It is the largest and most superficial muscle in the chest area. 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 innervated by the medial (C8-T1) and lateral (C5-C7) pectoral nerves, which originate from the medial and lateral cords, respectively. The pectoralis major has two distinct parts, the clavicular and sternocostal heads, which are responsible for different actions.
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 also contributes to adduction of the humerus. The clavicular head originates on the medial one-third to two-thirds of the clavicle and upper sternum.
The sternocostal part of the pectoralis major 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 head originates from the lower sternum, external oblique aponeurosis, and the costal cartilage of ribs 1-6. The posterior lamina of the sternocostal head forms a 90-degree cephalad turn before inserting into the humerus.
The primary functions of the pectoralis major are flexion, adduction, and internal rotation of the humerus. It is also responsible for keeping the arm attached to the trunk of the body. The pectoralis major can be targeted with various exercises, including single-joint and multi-joint movements. Heavy loads and high-impact contact sports, such as powerlifting, can lead to tears in the pectoralis major, which are uncommon but have become more prevalent in recent years.
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Connective tissue
The breasts have a complex anatomy involving various tissues, muscles, and ligaments. While there are no muscles within the breasts themselves, muscles play a crucial role in supporting the breasts and connecting them to the ribs, providing structural support.
One of the key connective tissues in the breast is the pectoral fascia, a flat sheet of connective tissue associated with the pectoralis major muscle. The base of the breast lies on this fascia, and it acts as an attachment point for the suspensory ligaments. The pectoralis major muscle is a large chest muscle that provides structural support for the breasts. Additionally, there is a layer of loose connective tissue called the retromammary space between the breast and the pectoral fascia. This space is often utilised in reconstructive plastic surgery.
The suspensory ligaments attached to the pectoral fascia also contribute to the structural integrity and support of the breasts. These ligaments provide additional connections between the breasts and the surrounding structures, helping to maintain the shape and position of the breasts.
Moreover, the breast's attachment to the chest wall involves a layer of connective tissue called the dermal brassiere. This connective tissue layer provides further support and stability to the breasts by connecting them to the underlying structures of the chest wall. The dermal brassiere consists of dense connective tissue that surrounds the breasts and extends to the chest wall, creating a supportive network.
In summary, while there are no muscles within the breasts themselves, connective tissue plays a crucial role in providing structural support and maintaining the shape of the breasts. The pectoral fascia, retromammary space, suspensory ligaments, and dermal brassiere all contribute to the complex network of connective tissue that supports the breasts and connects them to the surrounding structures, including the muscles and bones of the chest wall. This connective tissue layer is essential for breast anatomy and can influence the shape, position, and overall health of the breasts.
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Suspensory ligaments
The suspensory ligaments of the breasts, also known as Cooper's ligaments, are bands of tough, fibrous, flexible connective tissue that provide shape, structure, and support to the breasts. They maintain the breasts' contour and keep them in position, supporting them on the chest wall.
Cooper's ligaments extend from the dermis of the skin covering the breast to the deep fascia forming the bed of the breast. They are typically well-developed in the upper half of the breast, which helps prevent sagging or ptosis.
Over time, these ligaments can naturally stretch and loosen, causing the breasts to sag. This can be influenced by various factors, including age, weight fluctuations, body mass index, breast size, and genetic factors. Multiple pregnancies can also contribute to ligament stretching, as the skin and ligaments are repeatedly stretched during lactation and weight changes. Additionally, hormonal changes after pregnancy can cause milk glands to atrophy, further impacting the ligaments' support.
To help maintain the strength and elasticity of Cooper's ligaments, it is recommended to wear supportive and well-fitting bras, especially during pregnancy and breastfeeding. Maintaining good posture by standing or sitting with a straight back can also relieve pressure from the ligaments. Additionally, consistent practice of specific chest exercises can help strengthen, firm, and tone the chest area, potentially slowing down the process of sagging. However, once the breast ligaments have stretched, it cannot be reversed or repaired, even with surgery.
In certain conditions, such as inflammatory carcinoma of the breast, the suspensory ligaments can play a role in the change in appearance of the breasts. Blockage of the local lymphatic ducts causes swelling, and the skin becomes tethered by the ligaments, resulting in a dimpled appearance.
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Smooth muscle
In one study, cells composing the desmoplastic reaction expressed alpha-smooth-muscle actin in all 11 breast carcinomas examined. On the other hand, no immunostain was found in the stromal cells of 7 breast tissue samples defined as normal. Three of 9 cases of fibrocystic disease showed a minority of positively stained stromal cells, generally associated with epithelial hyperplasia.
Additionally, all 7 cases of sclerosing adenosis, 3 of 4 cases of diffuse papillomatosis, and all 3 intraductal papillomas exhibited a majority of immunoreactive stromal cells. Out of 11 circumscribed fibroadenomas analyzed, numerous stromal cells expressed low amounts of alpha-smooth-muscle actin.
The detection of this previously unsuspected stromal cell phenotype in nonmalignant mammary tissues may aid in characterizing the variant morphological aspects labelled as "fibrocystic disease". While the factors responsible for smooth-muscle differentiation in stromal cells are not yet fully understood, research in this area continues to enhance our understanding of breast anatomy and the role of smooth muscle in health and disease states.
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Blood vessel tone
The breasts are supported by the pectoralis major muscle, which forms the base of the breast. This muscle is a broad, fan-like muscle that originates from the lateral sternum and clavicle and inserts at the humeral head. It receives most of its blood from branches of the internal mammary and thoracoacromial arteries. The pectoralis major muscle is connected to the breast via the suspensory ligaments of Cooper, which traverse the breast tissue from the dermis of the skin down to the pectoralis fascia. These ligaments are not taut, allowing the breasts to maintain their natural mobility. However, with age, there is a loss of tension in these ligaments, which can result in breast ptosis.
The blood supply to the breasts is provided by various vessels, including the internal thoracic artery (also known as the internal mammary artery), a branch of the subclavian artery. The lateral part of the breast receives blood from four vessels: the lateral thoracic and thoracoacromial branches, which originate from the axillary artery, and the lateral mammary branches, which originate from the posterior intercostal arteries (derived from the aorta). These vessels supply the lateral aspect of the breast in the 2nd, 3rd, and 4th intercostal spaces. Additionally, the breast skin receives its blood supply from the subdermal plexus, which communicates with deep underlying arterioles supplying the breast parenchyma. Superficial veins are found along the anterior surface of the fascia, following the areola path under the nipple areolar complex, known as the venous plexus of Haller. Deep within the breast are large veins that drain into the chest wall veins.
The anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves innervate the breast. These nerves contain both sensory and autonomic nerve fibres, with the autonomic fibres regulating smooth muscle and blood vessel tone. The external oblique muscle, located on the anterolateral aspect of the thoracic wall, has a segmental blood supply originating from the inferior intercostal vessels. It borders the inferolateral wall of the breast and plays a role in supporting the overall structure.
While not directly related to muscle support, it is worth noting that the breast also has extensive lymphatic drainage. The lymphatic system, including lymph vessels, plays a crucial role in the body's immune system by transporting lymph fluid, which helps fight infections.
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Frequently asked questions
The pectoralis major muscle.
The pectoralis major muscle acts as an attachment point for the suspensory ligaments.
Suspensory ligaments are ligaments that support the breasts.
The connective tissue between the breast and the pectoral fascia (a flat sheet of connective tissue associated with the pectoralis major muscle) also supports the breasts.
The breasts are innervated by the anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves.
