Ch22: Actions of the Respiratory Muscles
CHAPTER 22 ACTIONS OF THE RESPIRATORY MUSCLES André de Troyer he so-called respiratory muscles are those muscles that caudally and ventrally from their costotransverse articula- Tprovide the motive power for the act of breathing. Thus, tions, such that their ventral ends and the costal cartilages although many of these muscles are involved in a variety of are more caudal than their dorsal parts (Figure 22-2B, C). activities, such as speech production, cough, vomiting, and When the ribs are displaced in the cranial direction, their trunk motion, their primary task is to displace the chest wall ventral ends move laterally and ventrally as well as cra- rhythmically to pump gas in and out of the lungs. The pres- nially, the cartilages rotate cranially around the chon- ent chapter, therefore, starts with a discussion of the basic drosternal junctions, and the sternum is displaced ventrally. mechanical structure of the chest wall in humans. Then, the Consequently, there is usually an increase in both the lateral action of each group of muscles is analyzed. For the sake of and the dorsoventral diameters of the rib cage (see Figure clarity, the functions of the diaphragm, the intercostal mus- 22-2B, C). Conversely, a displacement of the ribs in the cau- cles, the muscles of the neck, and the muscles of the abdom- dal direction is usually associated with a decrease in rib cage inal wall are analyzed sequentially. However, since all these diameters. As a corollary, the muscles that elevate the ribs as muscles normally work together in a coordinated manner, their primary action have an inspiratory effect on the rib the most critical aspects of their mechanical interactions are cage, whereas the muscles that lower the ribs have an expi- also emphasized.
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