Dominic Stone
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving downward and outward, enlarging the thoracic cavity and decreasing the pressure inside, helping the lungs expand to draw in air. During exhalation, the diaphragm relaxes, and the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. The intercostal muscles, including the external and internal intercostals, also play a crucial role in breathing. They work together with the diaphragm to ensure smooth and efficient breathing cycles. In addition to the primary respiratory muscles, there are accessory muscles that assist in breathing, such as the sternocleidomastoid and the scalenes, which elevate the rib cage. During exercise, the diaphragm acts as a flow generator, while the rib cage and abdominal muscles become active pressure generators.
| Characteristics | Values |
|---|---|
| Primary inspiratory muscles | Diaphragm and external intercostals |
| Accessory inspiratory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior, latissimus dorsi, serratus posterior superior, iliocostalis cervicis |
| Accessory expiratory muscles | Rectus abdominis, external oblique, internal oblique, transversus abdominis, iliocostalis, longissimus, serratus posterior inferior, quadratus lumborum |
| Function of the diaphragm | Contracts and flattens during inhalation, moves downward, enlarges the thoracic cavity, decreases pressure inside, and helps the lungs expand to draw in air |
| Function of the intercostal muscles | Work with the diaphragm to ensure smooth and efficient breathing cycles |
| Function of the sternocleidomastoid muscles | Elevate the sternum and clavicle, lifting the ribs during inhalation |
| Function of the abdominal muscles | Contract during forceful exhalation, press the abdominal organs upward into the diaphragm, reducing the volume of the thoracic cavity |
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What You'll Learn
The diaphragm
Diaphragmatic breathing, or abdominal/belly breathing, is a technique that focuses on engaging the diaphragm fully to take deep and refreshing breaths. It is beneficial for everyone, especially those with COPD, as it helps strengthen the diaphragm and improves breathing efficiency. To practice diaphragmatic breathing, one can lie on their back with bent knees and place one hand on their upper chest and the other on their belly. While inhaling slowly through the nose, the air should be directed towards the lower belly, causing the hand on the belly to rise while the hand on the chest remains still. During exhalation through pursed lips, the abdominal muscles are tightened, and the diaphragm relaxes and moves upward in the chest cavity.
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Intercostal muscles
The external intercostal muscles are the outermost layer. They lie directly under the skin and originate from the lower border of the rib above, running obliquely and inserting into the upper border of the rib below. During inhalation, they elevate the ribs and bend them more open, thus expanding the chest wall and the transverse dimensions of the thoracic cavity. The external intercostals facilitate forced inspiration and aid in quiet and forced inhalation.
The internal intercostal muscles are the intermediate layer. They originate from the costal groove near the inferior border of the rib above and insert into the upper border of the rib below. They help collapse the lung during expiration, depressing the ribs and bending them inward, thus decreasing the transverse dimensions of the thoracic cavity. The internal intercostal muscles aid in forced expiration.
The innermost intercostal muscles are the deepest layer, separated from the internal intercostals by a neurovascular bundle. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals, and insert into the superior border of the immediate rib below. They assist the internal and external intercostals in their function, aiding in forced expiration.
Intercostal muscle strains are usually associated with physical trauma, such as a fall or car accident, or overexertion in contact or high-thrust sports. Symptoms include pain, muscle tension and stiffness, inflammation, and a change in breathing patterns.
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Accessory muscles
The accessory inspiratory muscles are the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the inferior fibres of serratus anterior and latissimus dorsi, and the serratus posterior superior. These muscles lift the third, fourth, and fifth ribs to increase space for air in the lungs. The sternocleidomastoid muscles originate from the manubrium of the sternum and sternal end of each clavicle, allowing them to elevate the sternum and clavicle, subsequently lifting the ribs during inhalation. The scalenus anterior muscles extend from the anterior tubercles of transverse processes of C3 to C6 vertebrae to the first rib, contributing to its elevation.
The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis. These muscles press the abdominal organs upward into the diaphragm, reducing the volume of the thoracic cavity. In the thoracolumbar region, the lowest fibres of iliocostalis and longissimus, the serratus posterior inferior, and quadratus lumborum are also accessory expiratory muscles.
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Exhalation and inhalation
The process of breathing involves inhalation and exhalation, which are made possible by the contraction and expansion of the thoracic cavity. The diaphragm, a dome-shaped muscle that separates the abdominal cavity from the thoracic cavity, is the primary muscle responsible for breathing. During inhalation, the diaphragm contracts and flattens, moving downward. This movement compresses the abdominal cavity, raises the ribs upward and outward, and expands the thoracic cavity, allowing air to enter the lungs.
The intercostal muscles, including the external and internal intercostals, also play a role in inhalation. They work together with the diaphragm to ensure smooth and efficient breathing cycles. The external and internal intercostals do not function independently during breathing but are assisted by the sternocleidomastoid and scalene muscles on the neck. These accessory muscles help elevate the rib cage and are consistently active during quiet breathing.
During exhalation, the diaphragm and intercostal muscles relax, causing a decrease in lung volume. This relaxation of the respiratory muscles increases the intrapulmonic pressure, which becomes higher than the atmospheric pressure. As a result, air flows out of the lungs until the intrapulmonic and atmospheric pressures equalize.
In addition to the diaphragm and intercostal muscles, other muscles contribute to efficient breathing. The abdominal muscles, including the rectus abdominis, transverse abdominis, external oblique, and internal oblique, become active during forceful exhalation or when lung elasticity is reduced. These muscles press the abdominal organs upward into the diaphragm, reducing the volume of the thoracic cavity.
During exercise, the expiratory muscles, including the abdominal muscles, play a more active role in breathing. They work in coordination with the inspiratory rib cage muscles to prevent rib cage distortion and optimize breathing mechanics.
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Abdominal muscles
The abdominal muscles are the accessory expiratory muscles, which assist in breathing but do not play a primary role. They are the rectus abdominis, external oblique, internal oblique, and transversus abdominis.
During quiet breathing, there is little to no muscle contraction involved in exhalation. However, when forceful exhalation is required, or when lung elasticity is reduced, active exhalation can be achieved by contracting the abdominal wall muscles. These muscles press the abdominal organs upward into the diaphragm, reducing the volume of the thoracic cavity.
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving its centre downward and its edges upward. This compresses the abdominal cavity, raising the ribs and expanding the thoracic cavity. When the diaphragm relaxes, the elastic recoil of the lungs causes exhalation.
The abdominal muscles can be strengthened through diaphragmatic breathing exercises. These exercises can improve breathing and alleviate symptoms of respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD). To perform diaphragmatic breathing, lie on your back with one hand on your chest and the other on your belly, just below your rib cage. Breathe in slowly through your nose, letting the air move towards your lower belly. The hand on your chest should remain still, while the one on your belly rises. Tighten your abdominal muscles and let them fall inward as you exhale through pursed lips.
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Frequently asked questions
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so that its centre moves caudally (downward) and its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs upward and outward, and thus expands the thoracic cavity. This expansion draws air into the lungs.
The intercostal muscles, the parasternals, the scalene, the neck muscles, and the abdominal muscles all play a role in breathing. The intercostal muscles work with the diaphragm to ensure smooth and efficient breathing cycles. The abdominal muscles are expiratory, while the scalene and neck muscles are inspiratory.
Accessory muscles of respiration are muscles that assist, but do not play a primary role, in breathing. The sternocleidomastoid and the scalenes (anterior, middle, and posterior) are typically included, as they assist in elevating the rib cage. Other accessory muscles include the serratus anterior, pectoralis major, and pectoralis minor.
The abdominal muscles are the primary muscles involved in exhalation. During forceful exhalation, the abdominal wall muscles contract, pressing the abdominal organs upward into the diaphragm, reducing the volume of the thoracic cavity and forcing air out of the lungs.
