Logan Steele
The muscles of respiration are the muscles that enable inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity. The diaphragm is the primary muscle responsible for breathing, but other muscles, such as the intercostal muscles, abdominal muscles, and neck muscles, also play a role in the process of respiration. During inhalation, the diaphragm contracts and moves downward, expanding the lungs and drawing air into them. During exhalation, the diaphragm relaxes, and the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. Accessory muscles of respiration, such as the sternocleidomastoid and the scalenes, assist in breathing but do not play a primary role. These muscles may be recruited during exercise or in cases of respiratory distress.
| Characteristics | Values |
|---|---|
| What are the muscles of respiration | The muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity |
| Which muscles drive respiration during quiet breathing | The diaphragm and, to a lesser extent, the intercostal muscles |
| Which is the major muscle responsible for breathing | The diaphragm |
| Which muscles are accessory muscles of respiration | Sternocleidomastoid, scalenes, trapezii, latissimus dorsi, platysma, and pectoralis major and minor muscles |
| Which muscles are involved in non-respiratory functions | Diaphragm |
| Which muscles are controlled by both voluntary and involuntary mechanisms | The muscles of respiration |
| Which muscles are inspiratory muscles | Diaphragm, external intercostals, scalene muscles, sternomastoids |
| Which muscles are expiratory muscles | Abdominal wall muscles, including rectus abdominus, internal and external obliques, and transversus abdominus |
| Which muscles are involved in breathing during physical activity | The muscles between the ribs, i.e., the intercostal muscles |
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The diaphragm
During inhalation, the diaphragm contracts, causing its centre to move downward and its edges to move upward. This movement compresses the abdominal cavity and raises the ribs upward and outward, thereby expanding the thoracic cavity. This expansion of the thoracic cavity creates a vacuum, which draws air into the lungs.
When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. The diaphragm returns to its dome-shaped resting position, and the lungs expel air due to the surface tension and elastic recoil.
In addition to its respiratory function, the diaphragm also has non-respiratory roles. It helps to increase intra-abdominal pressure, aiding in expelling vomit, faeces, and urine from the body. Furthermore, the diaphragm prevents acid reflux by exerting pressure on the oesophagus as it passes through the oesophageal hiatus.
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Intercostal muscles
The intercostal muscles are a group of muscles that are attached between the ribs. They are named after the Latin words that mean "between ribs". These muscles are responsible for changing the size of the space inside the rib cage, thereby facilitating breathing. The intercostal muscles are divided into three types: external, internal, and innermost intercostal muscles.
The external intercostal muscles are the frontmost of the intercostal muscles and are responsible for inhalation. They connect the ribs and contract to lift the rib cage, thereby expanding the chest cavity. This creates suction, pulling air into the lungs. The contraction of these fibres raises each rib toward the rib above, ultimately raising the rib cage and assisting in inhalation.
The internal intercostal muscles are located right behind the external intercostal muscles. They are responsible for exhalation. When these muscles contract, they work in opposition to the external intercostals, causing the rib cage to lower and reducing the chest cavity. This pushes air out of the lungs and makes you exhale. The internal intercostals are the most important respiratory muscles for normal speech and singing, as they are responsible for propelling air out through the mouth and nose.
The innermost intercostal muscles are the deepest layer of intercostal muscles and they support the internal intercostal muscles during exhalation. Together, the internal and external intercostal muscles work like rowing teams pulling in sync to facilitate the breathing process.
The intercostal muscles also contribute to other respiratory functions, such as forcefully pushing air out of the lungs when sighing or coughing. They receive their blood supply from anterior and posterior intercostal arteries, as well as internal thoracic and musculophrenic arteries.
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Abdominal muscles
The abdominal muscles play a crucial role in respiration, acting as accessory expiratory muscles. These muscles include the rectus abdominis, external oblique, internal oblique, and transversus abdominis. During inspiration, the contraction of the abdominal muscles lengthens the diaphragm, allowing it to maintain its optimal length for tension generation. This action also reduces the compliance of the abdominal compartment, enabling the area in contact with the rib cage to act as a fulcrum for the expansion of the lower rib cage.
The abdominal muscles undergo contraction and relaxation, altering the volume of the thoracic cavity and, consequently, the lungs. This movement of the abdominal muscles aids in producing inspiration and expiration. The internal oblique and transverse abdominis muscles are particularly sensitive to increases in chemical or volume-related drive. Additionally, abdominal breathing, a popular practice in fitness routines, has been found to have a deteriorating effect on postural stability and an increasing effect on respiratory muscle activation.
The diaphragm, a primary inspiratory muscle, is crucial for breathing. It separates the thoracic and abdominal cavities and contributes to inhalation and exhalation by lengthening and shortening the thoracic cavity. During inhalation, the diaphragm contracts, compressing the abdominal cavity and raising the ribs, which expands the thoracic cavity and draws air into the lungs. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out.
The intercostal muscles, including the external intercostals, are another important group of respiratory muscles. These muscles are attached between the ribs and assist in manipulating the width of the rib cage. The contraction of the external intercostal fibres raises each rib towards the rib above, elevating the rib cage and aiding inhalation. The internal intercostal muscles, while less crucial, also contribute to respiration during quiet breathing.
Additionally, several accessory muscles assist in respiration, particularly during periods of increased respiratory effort. These include the sternocleidomastoid, scalenes, serratus anterior, pectoralis major and minor, trapezius, and latissimus dorsi, among others. The involvement of these muscles can vary depending on the respiratory volume and breathing rate.
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Accessory muscles
The diaphragm and intercostal muscles are the primary muscles for respiration. 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 downwards and its edges upwards. This compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, drawing air into the lungs. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs.
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Thoracic cage
The thoracic cage, also known as the rib cage, is a vital component of the thoracic wall. It is a bony framework that encloses and protects the heart, lungs, and other vital organs. The thoracic cage is composed of the thoracic skeleton, which includes the sternum, 12 pairs of ribs, and 12 thoracic vertebrae, along with the associated costal cartilages and intervertebral discs.
The thoracic cage provides the necessary rigidity for organ protection and weight support for the upper limbs. It also serves as an anchorage for muscles, allowing for the expansion and contraction of the thoracic cavity during respiration. This expansion and contraction facilitate the movement of air into and out of the lungs. The flexibility of the ribs and their joints enables the thoracic cage to be dynamic, allowing for pulmonary ventilation.
During inhalation, the diaphragm contracts, moving caudally (downward) and compressing the abdominal cavity. This downward movement of the diaphragm raises the ribs outward and upward, expanding the thoracic cavity and drawing air into the lungs. The diaphragm is the major muscle responsible for breathing and separates the thoracic and abdominal cavities.
In addition to the diaphragm, the intercostal muscles also play a crucial role in respiration. These muscles are attached between the ribs and help manipulate the width of the rib cage. There are three layers of intercostal muscles, with the external intercostals being the most important in respiration. The contraction of these fibres raises each rib, ultimately elevating the rib cage and assisting in inhalation.
Other accessory muscles, such as the sternocleidomastoid and the scalenes, also contribute to respiration by assisting in elevating the rib cage. These muscles become active during increased respiratory volume or when breathing at the maximal flow rate.
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Frequently asked questions
The muscles of respiration are the diaphragm, rib cage muscles, and abdominal muscles.
The diaphragm is the primary muscle used for breathing. It is a dome-shaped muscle that separates the chest and abdominal cavities. During inhalation, the diaphragm contracts, moving downward and outward, compressing the abdominal cavity and expanding the chest cavity, which draws air into the lungs.
The diaphragm and external intercostals are the primary inspiratory muscles.
The abdominal muscles are the most important expiratory muscles. They contract and raise abdominal pressure, pushing air out of the lungs.
Accessory muscles assist in breathing but do not play a primary role. They include the sternocleidomastoid and the scalenes (anterior, middle, and posterior).
