Logan Steele
The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. The diaphragm is the major muscle of inspiration and is responsible for breathing. The intercostal muscles are attached between the ribs and manipulate the width of the rib cage. The accessory muscles of respiration can expand the rib cage and assist inspiration during situations of increased ventilatory demand, such as during exercise or when other inspiratory muscles are impaired.
| Characteristics | Values |
|---|---|
| Main function | Contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity |
| Primary muscles | Diaphragm, external intercostals |
| Accessory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior, latissimus dorsi, serratus posterior superior, serratus posterior inferior, levatores costarum, transversus thoracis, subclavius, abdominal muscles, etc. |
| Function of primary muscles | The diaphragm contracts and pulls the lower surfaces of the lungs downwards, compressing the abdominal cavity, raising the ribs upward and outward and thus expanding the thoracic cavity. This expansion draws air into the lungs. |
| Function of accessory muscles | Can expand the rib cage and assist inspiration during situations of increased ventilatory demand, such as during exercise or when other inspiratory muscles are impaired |
| Fatigue resistance | Training can improve the fatigue resistance and mechanical efficiency of respiratory muscles |
| Control | Respiratory muscles are controlled by both voluntary and involuntary mechanisms |
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What You'll Learn
The diaphragm is the main muscle for breathing
The diaphragm is a thin, dome-shaped muscle that sits under the lungs and separates the abdominal cavity from the thoracic cavity. It is the main muscle responsible for breathing. During inhalation, the diaphragm contracts, moving downward and compressing the abdominal cavity, while its edges move upward, raising the ribs and expanding the thoracic cavity. This expansion 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, and allowing the diaphragm to return to its dome shape.
The diaphragm works in coordination with other muscles during the breathing process. The intercostal muscles, for example, assist in respiration by manipulating the width of the rib cage. There are three layers of intercostal muscles, with the external intercostals being the most important in respiration. Their contraction raises the rib cage, aiding in inhalation. During exhalation, the abdominal muscles gradually relax, and the diaphragm is unloaded, acting as a flow generator.
The diaphragm is a critical muscle for maintaining respiratory health. Its efficient functioning can be improved through breathing exercises, such as diaphragmatic breathing. This technique helps to reduce blood pressure and heart rate, improve relaxation, and increase oxygen levels in the blood.
Any disruption to the diaphragm's function can have significant consequences. Conditions such as chronic obstructive pulmonary disease (COPD) can weaken and flatten the diaphragm, causing breathing difficulties. Other issues like acid reflux, heartburn, and chest pain may also be indicative of diaphragm problems. Therefore, the diaphragm, as the primary muscle of respiration, requires attention and care to ensure optimal respiratory health.
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Intercostal muscles aid inhalation and exhalation
The intercostal muscles are one of the most important groups of respiratory muscles. They aid inhalation and exhalation by manipulating the width of the rib cage. The intercostal muscles are attached between the ribs and consist of three layers: external, internal, and innermost intercostal muscles.
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, they raise each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation. The contraction of the external intercostal muscles lifts the ribs and expands the rib cage, aiding inhalation.
The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. The contraction of these muscles has the opposite effect of the external intercostals: they lower the ribs and reduce the rib cage, aiding exhalation. During exhalation, the internal intercostal muscles work with the diaphragm to push air out of the lungs.
The innermost intercostal muscles are the least well-understood of the three layers. They are an incomplete muscle layer, crossing more than one intercostal space. These muscles assist the function of the external and internal intercostal muscles.
The intercostal muscles work in coordination with other respiratory muscles, such as the diaphragm and abdominal muscles, to optimise the mechanics of breathing. The diaphragm is the major muscle responsible for breathing and works in conjunction with the intercostal muscles to aid inhalation and exhalation.
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Accessory muscles assist breathing during exercise
The muscles of respiration are the muscles that contribute to inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. 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 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. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome shape.
The accessory muscles of respiration are muscles that assist, but do not play a primary role in breathing. They are recruited during exercise because of the increased metabolic need. They are also used during dysfunction in the respiratory system. The accessory inspiratory muscles are the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the serratus anterior, and the latissimus dorsi. The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis.
During exercise, the mechanics of the breathing pattern are regulated so precisely that the work performed by the respiratory muscles is minimised. At higher levels of exercise, the pressures produced by the respiratory muscles are well below their maximum. At maximal exercise, the oxygen consumed by the respiratory muscles to breathe is only about 10% of the total. However, this is only true for healthy subjects, not those who are trained athletes.
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Respiratory muscles are trained to improve endurance
The muscles of respiration are the muscles that contribute to inhalation and exhalation, aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. The elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.
The diaphragm is the major muscle of inspiration, accounting for approximately 70% of the inhaled tidal volume in a normal individual. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so its center 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. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome shape.
The intercostal muscles are thin sheets of muscular fibers that run between the ribs in the costal spaces. There are two sheets of muscle fibers, the external and internal intercostals. The external intercostals function to expand the rib cage during inspiration. The internal intercostals are deeper and function to decrease rib cage size during expiration.
The accessory muscles of respiration can expand the rib cage and assist inspiration during situations of increased ventilatory demand, such as during exercise or when other inspiratory muscles are impaired. These include the sternocleidomastoid, scalenes, trapezii, latissimus dorsi, platysma, and pectoralis major and minor muscles.
Respiratory muscle training has been shown to have a small but probable and significant effect on endurance exercise performance. This is because the respiratory muscles, like the heart, form an organ system that acts as a pump. The primary task of the respiratory pump is to displace the chest wall and control airway tone in a rhythmic and coordinated action to ventilate the gas-exchange units of the lung to maintain arterial blood gas and pH homeostasis. Training these muscles can improve their endurance and performance, allowing for better ventilation and endurance during exercise.
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Damage to nerves in the spinal cord can cause respiratory failure
The respiratory system involves inhaling oxygen into the blood and exhaling carbon dioxide out. The diaphragm is the primary 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, compressing the abdominal cavity and raising the ribs outward and upward, thereby expanding the thoracic cavity and drawing air into the lungs. When the diaphragm relaxes, the thoracic cavity contracts, and air is forced out of the lungs.
The intercostal muscles are another important group of respiratory muscles. These muscles are attached between the ribs and are crucial for manipulating the width of the rib cage. The contraction of these muscles raises each rib toward the one above it, with the overall effect of raising the rib cage and assisting in inhalation.
Damage to the nerves in the spinal cord can cause respiratory failure. Spinal cord injury (SCI) can result in a loss of muscle control needed for breathing and coughing, depending on the injury level and whether the injury is complete or incomplete. Signals from the brain may be limited or blocked as they try to pass beyond the damaged area of the spinal cord, reducing the brain's control over the muscles used for breathing and coughing. A complete injury above the C5 level of injury will typically result in impaired diaphragm function and the need for mechanical ventilation.
Respiratory muscle training regimens may improve inspiratory function after SCI. Techniques such as diaphragm pacing, phrenic nerve pacing, and unilateral diaphragm pacing are used to wean patients off ventilators and reduce the risk of respiratory failure.
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Frequently asked questions
Respiratory muscles are the muscles that contribute to inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity.
The diaphragm is the major muscle of inspiration and is, therefore, a crucial respiratory muscle. The intercostal muscles are also considered respiratory muscles and are important in manipulating the width of the rib cage.
During inhalation, the diaphragm contracts, so 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. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs.
Damage to the nerves in the upper spinal cord can interfere with the movement of the diaphragm and other muscles in the chest, neck, and abdomen. This can cause respiratory failure, and ventilator support or oxygen therapy may be required to maintain oxygen levels in the body.
