Muscles of respiration: types, characteristics and functions

Breathing is one of the basic processes carried out by our body, and one of the most fundamental for survival.

Every time we inhale we introduce oxygen into our body, which allows the subsistence of the cells of our body. At the same time, with each exhalation, we expel waste such as CO2, something that allows us to clean the body of the remains of cellular activity.

But the act of breathing, although semi-conscious (can be voluntarily controlled although is usually carried out unconsciously), requires a series of muscular movements to be able to occur. And there are multiple muscles of respiration that are mobilized for it. Throughout this article let's see what are the muscles of respiration, both the most relevant and others that although less essential also have a role in the process.

• Related article: "Controlled Breathing: what it is and how to use it"

Major muscles of respiration

Next we will see the main and most relevant muscles that participate and allow the respiratory process. Although there are many ways to classify them into different categories, this time we are going to divide them into four main groups.

1. Diaphragm

The diaphragm is one of the main and most important respiratory muscles, as well as being among the best known.

Is about a cylindrical muscle of relatively large size, with a dome also formed by tendon tissue and which is located below the lungs and ribs.

This muscle, which separates the torso from the abdomen, is key in both inspiration and experimentation processes. As it contracts, it moves the viscera downward, leaving space and raising the thoracic cavity in such a way as to allow the lungs to expand.

2. Intercostal muscles

The second large group of muscles that are essential for respiration are the intercostals, which allow displacement of the rib cage which in turn enables lung expansion. We can find two types of intercostal muscle.

2.1. External intercostal

Muscle that covers the inner area of ​​the ribs and that results in a muscular subgroup of greater importance when it comes to allowing breathing. It is essential when it comes to being able to inspire, since they are the ones that open the rib cage and allow lung expansion.

2.2. Internal intercostal

The internal intercostal muscles have a predominantly exhalation function: their contraction causes the ribs to go down, returning to its starting position.

• You may be interested: "Neuromuscular junction: the bridge between neuron and muscle"

3. Abdominal muscles

The abdominal muscles are a series of muscles located in the abdomen and actively participating in the respiratory process. Technically they are not so essential when it comes to maintaining unconscious breathing, but they actively participate in voluntary expiration.

3.1. Internal obliques

These muscles are found on the front and side of the abdomen and they are especially relevant in allowing consciously controlled breathing. It allows flexing the thorax, making the diaphragm stretch and facilitating inspiration. It also allows the completion of expiration by moving the wall of the belly inward.

3.2. External obliques

The external obliques are the outermost anterior and lateral muscles that can be seen around the rectus abdominis. These muscles perform functions similar to those of the internal obliques, favoring inspiration and participating in forced or voluntary expiration.

3.3. Rectus abdominis muscle

One of the abdominal muscles whose movement is most visible during breathing, is divided into several intersections separated by connective tissue and extending from the pubis to the lower part of the cage thoracic. Along with the oblique muscles, pulls the lower ribs down and facilitates expiration. It allows to compress the lower part of the chest.

3.4. Transverse muscle

The transverse muscle may be attached to the internal oblique. It is the deepest muscle between the widths of the abdomen, and runs from the spine to the linea alba and from the ribs (inserted into ribs from seven to twelve). It helps to compress the abdominal viscera and the lower part of the chest, and participates in voluntary breathing both in inspiration and especially in expiration.

4. Accessory muscles

Within the group of accessory muscles we include the set of muscles that although they are not the main responsible for respiratory movement do have a relevant role in that it is produce. We will include in it muscles that could be considered part of the rest of the groups, but that are not so fundamental.

Similar to the abdominals, they are generally mobilized during forced respiratory movement, and especially in situations such as when there are breathing difficulties, coughs or intense physical exercise. Below we will see some of the best known, although there are many others involved to a greater or lesser extent in the respiratory process.

4.1. Scalenes: anterior, middle and posterior

The scalene muscles are a set of three muscles (anterior, middle and posterior scalene) located at the level of the neck and principles of the torso. They go from the cervical vertebrae to the first two ribs and participate in breathing by helping to raise the first two ribs, facilitating voluntary inhalation.

4.2. Sternocleidomastoid

Also located in the neck, although in the anterolateral part. It contributes to raising and dilating the rib cage with its contraction, facilitating the pumping movement and being something that can facilitate voluntary inhalation in cases of dire need.

Sternal retraction is often used in emergency situations and is in fact sometimes a sign of respiratory problems.

4.3. Trapezoids

The trapezius muscles are muscles that unite the man, the spine, the scapula and the skull, linking these areas and allowing, for example, the shoulders to remain in the same position when carrying weight. It consists of three parts: upper, middle and lower. They participate in the voluntary inhalation movement, by raising the rib cage when it contracts.

4.4. Pectoralis major

Located in the thorax and forming one of the most visible and powerful parts of the pectoral muscles, this muscle is also one of the accessories in breathing. It allows mechanical inspiration, since when the rib cage contracts it rises.

4.5. Pectoral minor

Located behind the pectoralis major, this muscle helps lift and rotate the scapula in such a way that it is away from the ribs. This allows and facilitates deep and voluntary inhalation.

4.6. Serratus muscles

Divided into major, anterior and posterior, the serratus muscles, which are found in the posterior thoracic part of the body and contribute to voluntary inspiration. Also participate in deep breathing in great efforts.

4.7. Supracostal muscles

It is about a dozen small muscles that are located between the ribs, and that help to raise them when they contract and retract them when they relax. They participate in both inspiration and expiration.

Bibliographical references:

• García-Talavera, I., Díaz Lobato, S, Bolado, P.R. and Villasante, C. (1992). Respiratory muscles. Archives of Bronconeumology, 28 (5). Madrid.
• Roussos, C.S and Macklem, PT, (1982). The respiratory muscles. N. Engl. J. Med, 307: 786-797.