Chapter 10 - Section 10.3 - Study Guide - Assess Your Learning Outcomes - Page 371: 1

The diaphragm is located between the thoracic and abdominal cavities. It is the prime mover of inspiration. It also has roles in coughing, sneezing, laughing, crying, weightlifting, parturition(labor) defecation, and urination. Its origin includes the xiphoid process of the sternum, ribs 7-12 and their costal cartilages, and the lumbar vertebrae. The insertion is on the central tendon of the diaphragm. The nerve that serves the diaphragm is the phrenic nerve, The phrenic nerve contains motor, sensory and sympathetic nerves. The External Intercostal Muscles There are 11 pairs of external intercostals between the ribs. Each one extends from a rib tubercle posteriorly to the beginning of a costal cartilage, anteriorly. If rib 1 is fixed, the external intercostals act to elevate and protract ribs 2-12. They expand the thorax during inspiration, and exercise a braking action on the process of inspiration. Innervation of these muscles is by the intercostal nerves. The Internal Intercostal muscles: There are 11 pairs of internal intercostals. They lie deep to the external intercostals, and run from the margin of the sternum to the edge of the ribs. During inspiration, these muscle elevate the ribs, and expand the thoracic cavity, In expiration, they depress and retract the ribs; this constricts the thoracic cavity and expels the air in forced expiration. These muscles originate on the superior margins of costal cartilages of ribs 2-12. and margin of the sternum. Each internal intercostal muscle inserts onto the margin of the rib above it . Innervation of these muscles is by the intercostal nerves.

The Innermost Intercostal Muscles These muscles run deep to the internal intercostals. Each innermost intercostal emerges from the internal surface of the rib above and inserts on the deep surface of the rib below. The contraction of these muscles reduces the transverse dimension of the thoracic cavity and helps to force air out of the lungs in forced expiration. Internal intercostal nerves serve these muscles.