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In reference to the muscles of the thoracic wall, the intercostal nerves and vessels run posterior to the internal intercostal muscles: therefore, they are generally covered on the inside by the parietal pleura, except when they are covered by the innermost intercostal muscles, innermost intercostal membrane, subcostal muscles or the transversus thoracis muscle.
Internal intercostal muscles also known as intercostalis internus aid in forced expiration (quiet expiration is a passive process). They originate on ribs 2–12 and have their insertions on ribs 1–11.Their fibers pass anterior and superior from the upper margin of the rib and costal cartilage to the lower margin of the rib above. [2]
The internal intercostal muscles (intercostales interni) are a group of skeletal muscles located between the ribs.They are eleven in number on either side. They commence anteriorly at the sternum, in the intercostal spaces between the cartilages of the true ribs, and at the anterior extremities of the cartilages of the false ribs, and extend backward as far as the angles of the ribs, hence ...
The spaces between the ribs are known as intercostal spaces; they contain the instrinsic intercostal muscles and the neurovascular bundles containing intercostal nerves, arteries and veins. [4] The superficial surface of the rib cage is covered by the thoracolumbar fascia , which provides external attachments for the neck , back , pectoral and ...
There are three layers of intercostal muscles. The external intercostal muscles are most important in respiration. These have fibres that are angled obliquely downward and forward from rib to rib. [2] The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.
[2] [3] It can also be used for applying a nerve block known as the rhomboid intercostal block, which can be used to relieve pain after rib fractures, and a thoracotomy. This nerve block is usually achieved by injection of the local anesthetic agent into the fascial plane between the rhomboid upper intercostal muscle and the rhombic muscles.
Passing backward, it splits into the deep cervical artery and the supreme intercostal artery (highest intercostal artery), which descends behind the pleura in front of the necks of the first and second ribs, and anastomoses with the first aortic intercostal (3rd posterior intercostal artery). As it crosses the neck of the first rib it lies ...
These muscles work in unison when inhalation occurs. The internal intercostal muscles relax while the external muscles contract causing the expansion of the chest cavity and an influx of air into the lungs. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below.