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ANA 534 T2 ATW
learning objective answers to anterior thoracic wall
Question | Answer |
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Name the muscles of the thoracic wall that anchor to the thoracic cage to act as accessory muscles of respiration. | The serratus posterior superior, serratus posterior inferior and the levator costarum. |
What is the function of the serratus posterior superior and inferior? | Superior elevates the upper 4 ribs to increase thoracic volume. The serratus posterior inferior pulls down on the ribs preventing the diaphragm from pulling them up. This allows the diaphragm to effectively increase the thoracic volume as well. |
List the remaining muscles that are found within the intercostal space - from superficial to deep. | External intercostal, internal intercostal, and the 3rd layer composed of - from front to back: transversus thoracis, innermost intercostals, and subcostals. |
In which direction do the fibers of each of the layers extend? | External intercostals are directed inferior and medially (hands-in-pockets); internal intercostals go upward and medially (opposite to the externals), and the innermost intercostals are oriented in a similar direction to the internals. |
Where does each fade into membranous attachments? | External intercostals become membranous anteriorly, internal intercostals become membranous posteriorly , and the muscles of the 3rd layer (transversus thoracis, innermost intercostals, and subcostals) are linked to one another by intervening membranes. |
Where does the intercostal neurovascular bundle run between them? | Between the internal and innermost intercostal layers. |
What are the 3 muscle groups that, when linked by a membrane, form the deepest layer of the intercostal mm.? | The transversus thoracis, innermost intercostals, and subcostals. |
From what vessel do the posterior intercostal aa. arise? | The aorta. |
From which vessel do their anterior counterparts arise? | The internal thoracic (mammary) artery. |
What structure(s) innervate the intercostal mm.? | The ventral rami of the true spinal (intercostal) nn. |
In what order is each intercostal neurovascular bundle arranged? | From superior to inferior: interostal vein, intercostal artery and intercostal nerve (VAN). |
What portion of the rib is designed to protect them? | The costal groove. |
Which component of the neurovascular bundle is least protected by this? | The intercostal nerve. |
What is the clinical implication of this? | Insertion of a needle for removal of fluid from pleural cavity should have needle placed mid-way between ribs to ensure intercostal nerve of upper rib is not punctured, nor is its collateral branch that passes close to the upper border of the lower rib. |
Which theory of referred pain comes into play if an intercostal nerve is injured? | Proximal-distal. |
What is the fascial layer found between the intercostal mm. and the pleura? | Endothoracic fascia. |
What is the function of this fascial layer? | It adheres the pleura to the back side of the thoracic musculature (innermost intercostal m. layer). |