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The diaphragm and intercostal muscles are the most important groups of muscles that control the lungs. The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdomen. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity and expanding the lungs. The intercostal muscles are attached between the ribs and control rib movement, assisting in inhalation and exhalation. During exhalation, the diaphragm and intercostal muscles relax, reducing the volume of the thoracic cavity, which results in air being pushed out of the lungs.
| Characteristics | Values |
|---|---|
| Main inspiratory muscle | Diaphragm |
| Primary inspiratory muscles | External intercostals |
| Accessory inspiratory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, inferior fibres of serratus anterior and latissimus dorsi, serratus posterior superior, iliocostalis cervicis |
| Muscles that help in forceful expiration | Internal intercostals, intercostalis intimi, subcostals, and abdominal muscles |
| Accessory expiratory muscles | Abdominal muscles |
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What You'll Learn
The diaphragm is the main inspiratory muscle
The diaphragm is the main muscle that controls inhalation or inspiration. Located below the lungs, it is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. During inhalation, the diaphragm contracts and flattens, and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs.
The diaphragm is attached to the base of the sternum, the lower parts of the rib cage, and the spine. As the diaphragm contracts, it moves down and increases the length and vertical diameter of the chest cavity, thereby expanding the lungs. This movement of the diaphragm during inspiration is called abdominal support. The diaphragm's capacity to generate pressure is enhanced during inspiration.
The intercostal muscles and neck muscles help move the rib cage and thus assist in breathing. The external intercostals in the dorsal portion of the rostral interspaces, the intercartilaginous portion of the internal intercostals (the so-called parasternal intercostals), and, in humans, the scalenes are also involved in expanding the rib cage during inspiration. By elevating the ribs and causing an additional fall in pleural pressure, these muscles help the diaphragm expand the chest wall and the lungs.
During exhalation, the diaphragm relaxes and returns to its domelike shape, and air is forced out of the lungs. Relaxed normal expiration is a passive process that happens because of the elastic recoil of the lungs and surface tension. However, during vigorous exercise, the abdominal muscles participate in exhalation. The abdominal muscles contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be pushed out.
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Intercostal muscles aid inhalation
The diaphragm is the major muscle of respiration, but the intercostal muscles also play a key role in inhalation. Intercostal muscles are found between the ribs and control rib movement. They are attached between the ribs and manipulate the width of the rib cage.
There are three layers of intercostal muscles: external, internal, and innermost. The external intercostal muscles are the most important in respiration. They have fibres that are angled obliquely downward and forward from rib to rib. When these fibres contract, each rib is raised towards the rib above it, with the overall effect of raising the rib cage and aiding inhalation.
The intercostal muscles contract and move the ribs upwards and outwards. This increases the size of the chest and decreases the air pressure inside it, which sucks air into the lungs. The diaphragm contracts and moves downwards, increasing the length and diameter of the chest cavity, and the lungs expand into the space.
The muscles of inhalation, or inspiration, elevate the ribs and sternum. They are composed of fatigue-resistant muscle fibres and are controlled by both voluntary and involuntary mechanisms. This means that we can take a breath when we want to, but our bodies will also automatically breathe without us having to think about it.
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Abdominal muscles aid exhalation
The diaphragm is the major muscle of respiration, driving quiet breathing by contracting and flattening during inhalation, creating a vacuum that pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its dome shape, forcing air out of the lungs. The diaphragm is assisted by the intercostal muscles, which help move the rib cage and manipulate the width of the rib cage.
During quiet breathing, there is little to no muscle contraction involved in exhalation. Instead, the process is driven by the elastic recoil of the lungs. However, during vigorous exercise or when playing a wind instrument, exhalation becomes an active process, and several muscles participate in this process.
The abdominal muscles are the most important muscles involved in forceful exhalation. They contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be expelled. The abdominal muscles involved in exhalation include the rectus abdominis, transverse abdominis, external oblique muscle, and internal oblique muscle. The rectus abdominis pulls the ribs down during active expiration. Its point of origin is the pubic symphysis and pubic crest, and it attaches to the xiphoid process and the 5th to 7th costal cartilages.
The internal intercostal muscles are also involved in forceful exhalation. These muscles have fibres that are angled obliquely downward and backward from rib to rib. During exhalation, the internal intercostal muscles work with the abdominal muscles to increase intra-abdominal pressure, pushing the diaphragm upwards and further reducing the size of the thoracic cavity.
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Exhalation is passive at rest
The diaphragm is the main muscle of respiration and is located below the lungs. It is a dome-shaped muscle that contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and producing lung expansion. During inhalation, the diaphragm contracts and flattens, creating a vacuum that pulls air into the lungs.
Exhalation, on the other hand, is a passive process at rest. It occurs due to the elastic recoil of the lungs and surface tension. When the inspiratory muscles relax, the elasticity of the lung tissue causes the lungs to return to their resting shape and expel air. This recoil of the lung tissue is the natural elastic recoil of the lung tissue, and it is accompanied by the relaxation of all breathing muscles. The diaphragm relaxes and returns to its dome shape, and the air is pushed out of the lungs. This process is known as quiet or eupneic breathing, and it occurs at rest without active thought.
The intercostal muscles, situated between each rib, and some muscles in the chest and neck are accessory muscles that aid in breathing. They can become active to increase airflow during exercise or activity. During vigorous exercise, the abdominal muscles become the most important muscles for exhalation. They contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be pushed out.
The muscles of respiration form a complex arrangement around the lungs, with all muscles attached to the human rib cage having the potential to cause a breathing action. The inspiratory muscles help in inhalation by expanding the thoracic cavity, while the expiratory muscles induce exhalation by compressing the thoracic cavity.
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The diaphragm is also crucial for exhalation
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity. It is the primary muscle responsible for inhalation, but it also plays a crucial role in exhalation. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity, which, in turn, expands the lungs.
During exhalation, the diaphragm relaxes and returns to its dome-shaped form, and air is forced out of the lungs. This process is passive and occurs due to the elastic recoil of the lungs and surface tension. However, during vigorous exercise or forceful exhalation, the abdominal muscles contract and push the diaphragm against the lungs, causing air to be expelled more rapidly. The abdominal muscles that participate in forceful exhalation include the rectus abdominis, transverse abdominis, external oblique muscle, and internal oblique muscle.
The diaphragm's movement during exhalation is, therefore, essential for maintaining the respiratory cycle. As it relaxes and moves upward, it reduces the volume of the thoracic cavity, allowing the lungs to deflate and expel carbon dioxide-rich air. This coordinated action of the diaphragm during inhalation and exhalation ensures efficient gas exchange and maintains the body's oxygen and carbon dioxide balance.
It is worth noting that the intercostal muscles also play a role in exhalation. These muscles, located between the ribs, control rib movement. During exhalation, the external intercostal muscles relax, allowing the ribs to move inwards and downwards, decreasing the size of the chest cavity and facilitating air expulsion from the lungs.
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Frequently asked questions
The diaphragm is the major muscle of respiration.
The diaphragm contracts and moves downward, increasing the space in the chest cavity, so the lungs can expand into it.
When the diaphragm relaxes, the lungs deflate, and air is forced out.
The intercostal muscles are the secondary muscles that aid respiration. They are attached between the ribs and help manipulate the width of the rib cage.
During vigorous exercise, the abdominal muscles contract and push the diaphragm against the lungs, forcing air out.
