Overview_of_the_Thoracic_Cage_and_Lungs - Overview of the...

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Overview of the Thoracic Cage and Lungs The thoracic cage is formed by the 3 parts of the sternum (manubrium, body and xiphoid process), the 12 thoracic vertebrae, and the ribs. An important landmark on the sternum is the sternal angle (angle of Louis) between the manubrium and the body (manubriosternal angle). It is adjacent to the attachment of the 2 nd rib, and at the level of the T4-T5 intervertebral disc. The xiphisternal joint is located at the inferior border of T9 vertebra, and demarcates the inferior limit of the central part of the thoracic cavity. The movements of the thoracic wall can be described by a “bucket handle” movement of the lower ribs, and a “pump handle” movement by the upper ribs and sternum. The “bucket handle” movment increases the transverse diameter of the thoracic cage, whereas the “pump handle” movement increases the AP diameter. The 11 intercostal spaces are located inferior to their correspondingly numbered rib. The contents of an intercostal space include muscles, nerves and vessels. There are 3 primary muscles. From superficial to deep, they are the external intercostals, internal intercostals, and the innermost layer of intercostals muscles. The external intercostal muscle has fibers that run in an anterior (medial) direction from superior to inferior rib (same direction as hands in your front pocket). They are muscles of inspiration. The internal intercostal muscle fibers run in the opposite direction, and are primarily accessory muscles of expiration. The innermost intercostals run similar to the internal intercostals. Anteriorly, the transversus thoracis muscle replaces the innermost intercostal. Two neurovascular bundles (consisting of intercostal artery, vein and nerve) are found within the intercostal space. The larger one is located within the costal groove along the inferior border of the rib . The arrangement from superior to inferior is vein, artery, and nerve. (A VAN sits below the rib.) The smaller neurovascular bundle travels along the superior border of the rib. When performing a thoracentesis, it is important to avoid the large neurovascular bundle on the inferior border of the rib. Therefore, the needle is inserted above the rib as it pierces the intercostal space. The 11 intercostal nerves and 1 subcostal nerve are derived from the ventral rami of spinal nerves T1-T12. The anterior intercostal arteries are mostly branches of the internal thoracic (mammary) artery which is a branch of the first part of the subclavian artery. The posterior intercostal arteries are mostly branches from the thoracic aorta. The intercostal veins drain into the azygos venous system. The pleura is a serous membrane that has two layers. The visceral layer intimately covers the lung and can not be dissected from it. The parietal layer covers the inner surface of the thoracic cavity (back of the ribs and intercostal muscles), diaphragm, and mediastinum. The parietal layer is divided into 4 sections: cervical, costal,
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This note was uploaded on 02/17/2012 for the course MPAS PA 602 taught by Professor Dr.laird during the Fall '10 term at Chatham University.

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Overview_of_the_Thoracic_Cage_and_Lungs - Overview of the...

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