| Muscles of respiration | |
|---|---|
 Muscles of the body's respiration | |
| Identifiers | |
| MeSH | D012132 |
| Anatomical terminology | |
Themuscles of respiration are themuscles that contribute toinhalation andexhalation, by aiding in the expansion and contraction of thethoracic cavity. Thediaphragm and, to a lesser extent, theintercostal muscles drive respiration duringquiet breathing. The elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.
Thediaphragm is the major muscle responsible forbreathing. It is a thin, dome-shaped muscle that separates theabdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so that 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 thelungs. When the diaphragm relaxes, elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome-shape.[1]The diaphragm is also involved in non-respiratory functions, helping to expelvomit,faeces, andurine from the body by increasing intra-abdominal pressure, and preventingacid reflux by exerting pressure on theesophagus as it passes through theesophageal hiatus.
Along with the diaphragm, the intercostal muscles are one of the most important groups of respiratory muscles. These muscles are attached between the ribs and are important in manipulating the width of the rib cage. There are three layers of intercostal muscles. Theexternal intercostal muscles are most important in respiration. These have fibres that are angled obliquely downward and forward from rib to rib.[2] The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising therib cage, assisting in inhalation.
Accessory muscles of respiration are muscles that assist, but do not play a primary role, in breathing. Use of these while at rest is often interpreted as a sign ofrespiratory distress.[3] There is no definitive list of accessory muscles, but thesternocleidomastoid and thescalenes (anterior, middle, and posterior) are typically included, as they assist in elevating the rib cage.[4] The involvement of these muscles seems to depend on the degree of respiratory effort. During quiet breathing, the scalenes are consistently physically active, while the sternocleidomastoids are quiet.[5] With an increase in the respiratory volume, sternocleidomastoids also become active.[6] Both muscles are simultaneously activated when one breathes in at the maximal flow rate.[5]
Apart from the above neck muscles, the following muscles have also been observed contributing to respiration:serratus anterior,pectoralis major andpectoralis minor,trapezius,latissimus dorsi,erector spinae,iliocostalis,quadratus lumborum,serratus posterior superior,serratus posterior inferior,levatores costarum,transversus thoracis,subclavius (Kendall et al., 2005). Thelevator labii superioris alaeque nasi muscle lifts thesides of the nostrils.
During quiet breathing, there is little or no muscle contraction involved in exhalation; this process is simply driven by theelastic recoil of the lungs. When forceful exhalation is required, or when the elasticity of the lungs is reduced (as inemphysema), active exhalation can be achieved by contraction of the abdominal wall muscles (rectus abdominis,transverse abdominis,external oblique muscle andinternal oblique muscle). These press the abdominal organs cranially (upward) into the diaphragm, reducing the volume of the thoracic cavity.[1]
Theinternal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib.[2] These muscles can therefore assist in lowering the rib cage, adding force to exhalation.[1]
| International | |
|---|---|
| National | |
| Other | |
