Maximus Gage
The diaphragm is the major muscle of respiration, located below the lungs. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts and flattens, 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 intercostal muscles are another important group of respiratory muscles, attached between the ribs, and are important in manipulating the width of the rib cage.
| Characteristics | Values |
|---|---|
| Primary function | Respiration |
| Other functions | Expelling vomit, faeces, and urine from the body; preventing acid reflux |
| Muscle type | Dome-shaped sheet of muscle |
| Location | Below the lungs, separating the abdominal cavity from the thoracic cavity |
| Nerve supply | Motor nerve supply by Phrenic nerve (C3 C4 C5) and sensory supply by phrenic nerve to central tendon |
| Contraction | Rhythmic and continual |
| Control | Mostly involuntary |
| Role in inhalation | Contracts and flattens, enlarging the chest cavity and creating a vacuum that pulls air into the lungs |
| Role in exhalation | Relaxes and returns to its dome shape, forcing air out of the lungs |
| Supporting muscles | Intercostal muscles, neck muscles, abdominal muscles |
| Accessory muscles | Sternocleidomastoid, scalenes, trapezii, latissimus dorsi, platysma, pectoralis major, pectoralis minor |
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What You'll Learn
The diaphragm is the primary muscle of respiration
The diaphragm is a dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. It is the primary muscle of respiration, and its movement up and down changes the length and diameter of the chest cavity, thereby expanding and contracting the lungs. During inhalation, the diaphragm contracts and flattens, and its centre moves caudally (downward) while its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, drawing air into the lungs.
The diaphragm is the major muscle responsible for breathing, and it is also involved in non-respiratory functions. For example, it helps to expel vomit, faeces, and urine from the body by increasing intra-abdominal pressure. It also prevents acid reflux by exerting pressure on the oesophagus as it passes through the esophageal hiatus. The diaphragm is attached to the base of the sternum, the lower parts of the rib cage, and the spine.
The intercostal muscles and neck muscles also help move the rib cage and assist in breathing. The external intercostal muscles are most important in respiration, with fibres that are angled obliquely downward and forward from rib to rib. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation. The internal intercostal muscles, on the other hand, have fibres that are angled obliquely downward and backward from rib to rib. These muscles assist in lowering the rib cage, adding force to exhalation.
During exhalation, the diaphragm relaxes and returns to its dome shape, and air is forced out of the lungs due to the elastic recoil of the lungs and surface tension. This process is passive and occurs due to the elastic recoil of the lungs and chest wall, which causes them to return to their resting shape and expel air. During vigorous exercise, the abdominal muscles are the most important in exhalation. They 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 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, 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.
However, the intercostal muscles also aid respiration. There are three layers of intercostal muscles: external, internal, and innermost. The external intercostal muscles are most important in respiration. These have fibres that are angled obliquely downward and forward from rib to rib. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.
The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. The internal intercostals pull down on the rib cage and push air out of the lungs. They are the most important respiratory muscles for normal speech and singing, as they are the muscles that propel air out through the mouth and nose.
The innermost intercostal muscles receive blood supply from anterior and posterior intercostal arteries.
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Accessory muscles assist inspiration
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, 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.
The intercostal muscles are another important group of respiratory muscles. These muscles 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 most important in respiration, assisting in inhalation by raising the rib cage.
Accessory muscles are those that assist but do not play a primary role in breathing. They are recruited during exercise due to increased metabolic need and during respiratory dysfunction. Accessory muscles are also used during deep inhalation, such as when swimming underwater or blowing out birthday candles. In healthy individuals, these muscles are not active during regular breathing, and their use at rest may indicate respiratory distress.
There is no definitive list of accessory muscles, but the sternocleidomastoid and the scalenes (anterior, middle, and posterior) are typically included. These muscles assist in elevating the rib cage. The scalenes are consistently physically active during quiet breathing, while the sternocleidomastoids are only activated with increased respiratory volume. Both muscles are simultaneously activated during maximal inhalation. Other muscles that have been observed contributing to respiration include the serratus anterior, pectoralis major and pectoralis minor, trapezius, latissimus dorsi, erector spinae, iliocostalis, quadratus lumborum, serratus posterior superior, serratus posterior inferior, levatores costarum, and transversus thoracis.
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Abdominal muscles assist exhalation
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 expands the thoracic cavity. This expansion draws air into the lungs.
The diaphragm is also involved in non-respiratory functions, such as helping to expel vomit, faeces, and urine from the body by increasing intra-abdominal pressure. It also prevents acid reflux by exerting pressure on the oesophagus as it passes through the esophageal hiatus.
During exhalation, the diaphragm relaxes, and the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs and returning to its dome shape. While expiration is usually a passive process, abdominal muscles are the most important muscles that participate in exhalation during vigorous exercise.
Abdominal muscles contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be pushed out. 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 also assist in forceful expiration by pulling the ribs downward and inward, further reducing the size of the thoracic cavity.
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Respiratory muscles are controlled by the brain
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 caudally (downward) and its edges move cranially (upward). 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.
The diaphragm is controlled by the respiratory centre located inside the brain stem. The respiratory centre consists of networks of neurons in the hindbrain (the pons and medulla) that direct the diaphragm and other muscles to produce pressure gradients that move air into and out of the lungs. The respiratory rhythm and the length of each phase of respiration are set by reciprocal stimulatory and inhibitory interconnections of these brain-stem neurons.
The respiratory muscles can also be influenced by higher brain centres and controlled voluntarily to a substantial degree. For example, we can suspend breathing by holding our breath, or change our breathing patterns when speaking or singing. The body's sensors play a role in this, sending signals to the respiratory neuronal networks in the brain. Chemoreceptors detect changes in blood oxygen levels and blood acidity, while mechanoreceptors monitor the expansion of the lung, the size of the airway, the force of respiratory muscle contraction, and the extent of muscle shortening.
In addition to the diaphragm, the intercostal muscles are one of the most important groups of respiratory muscles. These muscles are attached between the ribs and manipulate the width of the rib cage. The contraction of these fibres raises each rib toward the rib above, raising the rib cage and assisting in inhalation. The internal intercostal muscles have fibres that angle obliquely downward and backward from rib to rib, assisting in lowering the rib cage and adding force to exhalation.
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