Question 19

Next, describe the motions of the ribs and sternum during forced inspiration and expiration. Consider movements in the vertical, anterior-posterior and transverse planes. In the description, include the names of the moving structures and a description of their motion(s).

During forced inspiration: -the inferior ribs lift and move out/distally (like lifting a bucket handle) -the superior ribs move the sternum mores anteriorly with the superior portion barely moving and the inferior portion moving the most (like lifting a water-pump handle) During forced expiration: -the inferior ribs lower and move in/proximally (like lowering the water bucket handle) -the superior ribs move the sternum more posteriorly with the superior portion barely moving and the inferior portion moving the most (like lowering the water pump handle)

What is the main action performed by the internal intercostal muscles?

In forced expiration: the internal intercostals contract→ pulling the ribs inward and down→ decreased intrathoracic volume

What is the main action performed by the external intercostal muscles?

In forced inspiration: the external intercostals contract→ lifting the ribs upward and outward → increased intrathoracic volume

Describe the movement of the diaphragm during forced inspiration. How does the diaphragmatic motion influence thoracic dimensions?

The diaphragm contracts during inspiration that causes it move inferiorly thus increasing thoracic volume.

Describe the movement of the diaphragm during forced expiration. How does the diaphragmatic motion influence thoracic dimensions?

The diaphragm relaxes during expiration which causes it move superiorly thus decreasing thoracic volume.

Why is it critical that the integrity (tone) of the intercostal muscles be maintained?

The most important function of the intercostals is to maintain muscle tone so that the thoracic cage can serve as a rigid wall that can resist pressure changes within the thorax especially during inspiration.