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( Rib cage)
The human rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic (chest) cavity and supports the pectoral (shoulder) girdle, forming a core portion of the human skeleton. A typical human ribcage consists of 24 ribs, the sternum, costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, make up the thoracic wall, and provides attachments for the muscles of the neck, thorax, upper abdomen, and back. The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out. These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air. All ribs are attached in the back to the thoracic vertebrae. The upper seven true ribs (costae verae, vertebrosternal ribs, I-VII). are attached in the front to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.
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