Muscular Actions Of Breathing: What Happens When We Breathe?
Breathing is both an unconscious, or involuntary, action that we rely on to function seamlessly in the background, as well as a process that we can consciously steer. If we take up certain kinds of sports, like swimming or running, for example, we will have to learn to control how we breathe. But, it would definitely be problematic if we had to think about the essential task of breathing all the time. So what happens when we breathe? How does it work? In this article, we’ll take a look at the process of breathing and the muscles we use.
What is breathing?
Breathing happens when air moves in and out of the lungs. The technical term for that process is pulmonary ventilation. It happens when we inflate and deflate our lungs. There are many phrases used to describe different techniques for breathing during specific types of exercise or during specific practices to reduce the stress response, for example. However, no matter what kind of technique we employ, we breathe by inflating and deflating our lungs to draw oxygen-rich air in and push carbon dioxide-containing air out.
There are two phases to regular breathing: inhalation and exhalation. Inhalation is also called inspiration. Exhalation is also called expiration. Changes in pressure outside and inside the lungs create the air exchange that we call breathing. However, the lungs are passive. The lungs are not muscles, so we have to use other muscles to manage the exchange of pressure to move air in and out of our lungs.
Muscles of regular breathing
The diaphragm is the main muscle of respiration in regular breathing. However, two other muscles assist the actions of inspiration and expiration, the external and internal intercostals.
Diaphragm
The diaphragm is a particularly unique muscle. It attaches broadly in what is considered its origin to the lumbar vertebrae L1-L3 (and sometimes L4), the lower six costal cartilages, and the posterior surface of the xiphoid process. Then, it inserts onto itself at what is called the central tendon.
Intercostal muscles
The intercostal muscles are found between the ribs. You could understand their location from their name. The prefix “inter” means between. The word “costal” means rib. The external intercostals originate on the inferior (lower) border of the rib above and insert on the superior (upper) border of the rib below. As their names might suggest, the internal intercostals are deep to (underneath) the external intercostals. They originate on the inner border of the rib above and insert on the superior border of the rib below.
Process of regular breathing
In regular breathing, sometimes called “quiet breathing” or “breathing at rest,” as we inhale, the top of the diaphragm descends and flattens out somewhat. That action pulls on the connective tissue connection to the lungs. Simultaneously, the external intercostals contract and help lift the ribs up and out. During an inhale, there is a negative pressure in the lungs. Because the air outside the lungs is at a higher pressure, it gets drawn into the area of lower pressure in the lungs.
Then, as we exhale, the diaphragm relaxes and lifts up. The external intercostals also relax, allowing the ribcage to come in and down. The internal intercostals can also add some amount of contraction (depending on the intensity of our breathing) to assist in bringing the ribs down and in. When we are breathing at rest, exhalation is mostly a passive part of the breathing cycle. The elastic recoil of the tissues, as well as the change in the pressure difference inside and outside the lungs, pushes the air out.
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Secondary respiration
In some situations, during intense exercise for example, the muscles we recruit to inhale and exhale may differ. Additional muscles, called secondary respiratory muscles, are called into action when our breath is forced or when we have an increased need for more oxygen more quickly. That might include something short and acute, like a cough or sneeze, or a moment when we’ve abruptly knocked the primary breathing action offline (like falling or getting knocked down in sports). It could also be a situation where we have a more sustained need, like running, for more breath more quickly.
The main additional muscles incorporated in secondary respiration include the sternocleidomastoid, the three scalene muscles, and the four layers of abdominal muscles (rectus abdominis, internal and external obliques, and transverse abdominis).
When we need to get more air in more quickly, the sternocleidomastoid and scalene muscles help lift the ribcage up. Simultaneously, the intercostals lift the ribcage up and out to make space for an inhale. During a forced exhalation, like a cough or a sneeze for example, all four layers of abdominals contract along with the internal intercostals to push the air out.
Conclusion
Breathing is an essential process that is both voluntary and involuntary. We use muscular action to influence the pressure difference inside and outside of our lungs. That has the effect of either drawing air in or forcing air out. The diaphragm is always part of the action of breathing, but we may also recruit other secondary breathing muscles, depending on how much we are exerting ourselves.