Anatomy of the Moving Body by Theodore Dimon Jr

Author:Theodore Dimon, Jr. [Dimon, Theodore]
Language: eng
Format: epub
ISBN: 978-1-58394-687-9
Publisher: North Atlantic Books
Published: 2012-11-05T16:00:00+00:00

Figure 37: Ribs during exhalation and inhalation (Illustration 17.2)

When the muscles of the trunk are functioning properly, the ribs are able to move flexibly, but because of tension and postural distortion, they are typically fixed and quite rigid. When this happens, the entire thorax moves too much as a whole, and the diaphragm, the other main agent of breathing, becomes overworked to make up for the lack of movement in the ribs. Also, the rib cage as a whole becomes fixed in a wrong attitude, usually somewhat thrown backward and shortened in front and then held up, narrowing the back and preventing the free action and mobility of the ribs in breathing, as well as interfering with the general upright support of the trunk. When we are properly supported by the postural muscles and are not shortened in stature, this tends to re-orient the entire rib cage, which in turn allows a widening of the back and an increased mobility and action of the ribs.

There are two layers of rib, or intercostal, muscles which are responsible for breathing (Fig. 38). The external intercostals arise from the lower border of each rib and attach to the upper border of the rib below, running obliquely down and forward. Underneath this layer are the internal intercostals, which arise from the inner surface of each rib and slant down and back, in the opposite direction to the external intercostals, to attach to the rib below. The external intercostals function mainly to elevate the ribs, which increases the width of the thoracic cavity and therefore causes inspiration. The internal intercostals depress the ribs when actively breathing out.

Transversus thoracis lies on the inner surface of the lower part of the sternum (Fig. 39). Its fibers extend up and out, like the splayed fingers of a hand, and insert into the costal cartilages of the second, third, fourth, fifth, and sixth ribs. This muscle, which aids in forceful expiration, is the muscle that you can sometimes feel gripping in the inner chest; it contributes to the rigidity of the chest in many people who raise and fix the chest in speech and breathing.

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