Logan Steele
The muscles of respiration are those that enable inhalation and exhalation by facilitating the expansion and contraction of the thoracic cavity. The diaphragm is the primary muscle responsible for breathing, but other muscles, including the intercostal muscles, also play a role. During inhalation, the diaphragm contracts, causing it to flatten and increase the volume of the thoracic cavity, thereby drawing air into the lungs. When the diaphragm relaxes, the thoracic cavity contracts, forcing air out of the lungs. During exercise, other muscles, such as the abdominal muscles and internal intercostals, become important for respiration, assisting in the process of inhalation and exhalation.
| Characteristics | Values |
|---|---|
| Predominant muscle of respiration | Diaphragm |
| Diaphragm's function | Separates the abdominal cavity from the thoracic cavity |
| Diaphragm's shape | Thin and dome-shaped |
| Diaphragm's movement during inhalation | Contracts, moves caudally (downward) and edges move cranially (upward) |
| Diaphragm's movement during exhalation | Relaxes, curves upwards and returns to its dome shape |
| Diaphragm's role in non-respiratory functions | Helps expel vomit, faeces, and urine from the body; prevents acid reflux |
| Intercostal muscles' role | Manipulating the width of the rib cage |
| Number of layers of intercostal muscles | 3 |
| Most important intercostal muscles in respiration | External intercostals |
| External intercostals' movement during inhalation | Contract, pull ribs upwards and outwards (expanding chest) |
| External intercostals' movement during exhalation | Relax, pull ribs inwards and downwards (reducing breadth of chest) |
| Abdominal muscles' movement during inhalation | Relax |
| Abdominal muscles' movement during exhalation | Contract and push the diaphragm upwards |
| Accessory muscles' function | Assist main breathing muscles, especially during exercise or in those with airway pathologies |
| Examples of accessory muscles | Sternocleidomastoid, pectoralis minor, serratus anterior, scalene muscles |
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What You'll Learn
- The diaphragm is the primary muscle responsible for breathing
- Intercostal muscles aid in respiration and control the width of the rib cage
- Abdominal muscles are responsible for exhalation
- Accessory muscles provide additional power during respiration, e.g. during exercise
- Sternocleidomastoid and scalenes are neck muscles that assist in elevating the rib cage
The diaphragm is the primary muscle responsible for breathing
During exhalation, the diaphragm relaxes, allowing the elastic recoil of the lungs to cause the thoracic cavity to contract, forcing air out of the lungs and returning the diaphragm to its dome shape. The internal intercostal muscles are responsible for pulling the ribs inwards and downwards during exhalation, reducing the breadth of the chest. The abdominal muscles are also involved in forced exhalation, contracting and pushing the diaphragm upwards.
The diaphragm is crucial for quiet breathing, but during exercise, other muscles become important to respiration. These include the scalene muscles and sternomastoids, which help to raise and expand the upper ribs and sternum, and the external intercostals, which continue to assist in raising the rib cage. Accessory muscles may also be activated during more strenuous breathing to provide additional power, such as the sternocleidomastoid, pectoralis minor, and serratus anterior.
The diaphragm also has non-respiratory functions, including aiding in the expulsion of vomit, faeces, and urine by increasing intra-abdominal pressure. It also helps to prevent acid reflux by exerting pressure on the oesophagus as it passes through the diaphragm. The elasticity of the diaphragm is vital to the health of the respiratory system and its ability to function optimally.
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Intercostal muscles aid in respiration and control the width of the rib cage
The intercostal muscles are one of the most important groups of respiratory muscles. They aid in respiration and control the width of the rib cage. There are three layers of intercostal muscles: external, internal, and innermost. The external intercostal muscles are most important for respiration, with fibres that run obliquely downward and forward from rib to rib. When these fibres contract, they raise each rib towards the rib above, with the overall effect of raising the rib cage and assisting in inhalation. The internal and innermost intercostals aid in forced exhalation, depressing the ribs.
The intercostal muscles work alongside other muscles to aid in respiration. During inspiration, the external intercostals work with the scalene muscles to raise the upper ribs and sternum, increasing the dimensions of the thorax. The diaphragm, a thin, dome-shaped muscle that separates the abdominal and thoracic cavities, is the major muscle responsible for breathing. It contracts during inhalation, compressing the abdominal cavity and raising the ribs, which expands the thoracic cavity and draws air into the lungs. During quiet breathing, the diaphragm is the predominant muscle of respiration.
During active expiration, the abdominal muscles are the most important, driving intra-abdominal pressure. The internal intercostals also aid in expiration, depressing the ribs and forcing air out of the lungs. The accessory muscles, which assist but do not play a primary role in breathing, are recruited during exercise or respiratory dysfunction due to increased metabolic need. These include the sternocleidomastoid, scalenus anterior, medius, and posterior, and the pectoralis major and minor, among others.
The elasticity of the respiratory muscles is crucial to the health of the respiratory system and maximising its functional capabilities. The intercostal muscles, in particular, play a key role in manipulating the width of the rib cage and facilitating breathing. Their contraction and relaxation alter the volume of the thoracic cavity, producing inspiration and expiration.
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Abdominal muscles are responsible for exhalation
The diaphragm is the primary muscle responsible for respiration, and it is involved in inhalation or inspiration. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving caudally (downward) and cranially (upward), compressing the abdominal cavity and expanding the thoracic cavity, which draws air into the lungs.
Expiration or exhalation, on the other hand, is a passive process during quiet breathing, as the diaphragm relaxes and the elastic recoil of the lungs and chest wall returns to its resting volume. However, during active expiration, such as during exercise, the abdominal muscles become crucial.
The abdominal muscles, including the rectus abdominus, internal and external obliques, and transversus abdominus, contract and raise abdominal pressure during active expiration. This increase in intra-abdominal pressure pushes the diaphragm upwards, further into the thoracic cavity, reducing its volume. This compression of the thoracic cavity by the abdominal muscles during exhalation is a key mechanism in forcing air out of the lungs.
The rectus abdominis, in particular, pulls the ribs down during active expiration. It originates at the pubic symphysis and pubic crest and attaches to the xiphoid process and the 5th to 7th costal cartilages. This action of the abdominal muscles during exhalation is especially important during vigorous exercise or activities that require forced expiration, such as playing a musical instrument.
In summary, while the diaphragm is the chief muscle of inspiration, the abdominal muscles play a significant role in active expiration, contracting and increasing intra-abdominal pressure to facilitate exhalation.
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Accessory muscles provide additional power during respiration, e.g. during exercise
The muscles of respiration are those that contribute to inhalation and exhalation, aiding in the expansion and contraction of the thoracic cavity. The diaphragm is the primary muscle responsible for breathing, aided to a lesser extent by the intercostal muscles.
However, during exercise, many other muscles become important to respiration. Accessory muscles provide additional power during respiration, particularly during physical exertion when breathing demands increase. These muscles assist in expanding and contracting the thoracic cavity to facilitate adequate gas exchange. They are also crucial during respiratory distress due to medical conditions like asthma or COPD. Their role becomes especially pronounced during periods of increased oxygen demand, providing a much-needed boost to achieve effective respiration.
The accessory muscles of respiration refer to muscles that provide assistance to the main breathing muscles, primarily when additional power is needed. They include the sternocleidomastoid, scalene muscles, and various abdominal muscles. The sternocleidomastoid and scalene muscles assist in elevating the rib cage. During inspiration, the external intercostals raise the lower ribs up and out, increasing the dimensions of the thorax. The scalene muscles and sternomastoids also become involved, serving to raise and push out the upper ribs and the sternum.
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.
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Sternocleidomastoid and scalenes are neck muscles that assist in elevating the rib cage
The muscles of respiration are those that contribute to inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity. The diaphragm is the major muscle responsible for breathing, but other muscles become important during exercise.
The sternocleidomastoid and scalenes are neck muscles that assist in elevating the rib cage. They are accessory muscles of respiration, which means they assist but do not play a primary role in breathing. The sternocleidomastoid muscle (SCM) divides the neck into anterior and posterior triangles. It is a large, easily recognisable, and palpable muscle. The scalene muscles reside in the posterior triangle.
During quiet breathing, the scalenes are consistently physically active, while the sternocleidomastoids are quiet. However, with an increase in respiratory volume, the sternocleidomastoids also become active. Both muscles are simultaneously activated when one breathes in at the maximal flow rate.
Experiments in dogs have shown that the contraction of these muscles causes a large axial displacement of the sternum and ribs in a cephalad direction, expanding the rib cage along its anteroposterior and transverse diameters. This expansion of the rib cage aids in inhalation.
Other accessory muscles of respiration include the serratus anterior, pectoralis major and pectoralis minor, trapezius, latissimus dorsi, erector spinae, and iliocostalis.
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Frequently asked questions
The diaphragm is the main muscle of respiration, responsible for inhalation and exhalation by aiding in the expansion and contraction of 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.
Intercostal muscles are attached between the ribs and help to manipulate the width of the rib cage. The external intercostal muscles are most important in respiration, raising the rib cage and assisting in inhalation.
Accessory muscles of respiration are those that assist the main breathing muscles, particularly when additional power is needed, such as during exercise. These include the sternocleidomastoid and scalenes, which help to elevate the rib cage.
