Which of the following Muscles Contracts during Quiet (Passive) Expiration

When we breathe, our body uses a variety of muscles to facilitate the process of inhaling and exhaling. During quiet or passive expiration, the muscles used are different than those used during active expiration or forced exhalation. In this article, we`ll discuss which muscle contracts during quiet expiration.

To understand this, let`s first briefly go over the process of breathing. When we inhale, our diaphragm contracts and moves downwards, which expands the thoracic cavity and pulls air into the lungs. The intercostal muscles (located between the ribs) also contract and lift the rib cage, further expanding the thoracic cavity. This is called inspiration.

During passive expiration, the diaphragm and intercostal muscles relax. As a result, the thoracic cavity decreases in size and air is pushed out of the lungs. However, there is one muscle that does contract during quiet expiration – the internal intercostal muscles.

The internal intercostals are located between the ribs and run perpendicular to the external intercostals (which are used during inspiration). These muscles contract during quiet expiration and pull the ribs down, which decreases the size of the thoracic cavity and pushes air out of the lungs. This is a relatively gentle and slow process compared to forced exhalation, which involves the use of the abdominal muscles and other muscles in the torso.

It`s worth noting that not all muscles used during breathing are voluntary (i.e. under conscious control). The diaphragm, for example, is an involuntary muscle that contracts automatically in response to signals from the brainstem. However, we can consciously control our breathing to some extent by changing the depth and rate of our breaths.

In conclusion, the internal intercostal muscles are the primary muscles that contract during quiet or passive expiration. These muscles play an important role in helping us breathe evenly and efficiently, allowing us to go about our daily activities without even thinking about it. Understanding the mechanics of breathing can help us appreciate the complexity of our bodies and the importance of taking care of our respiratory health.