Muscles of respiration: Difference between revisions

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{{Short description|Muscles involved in breathing}}

The various '''muscles of respiration''' aid in both inspiration and expiration, which require changes in the pressure within the [[thoracic cavity]]. The respiratory muscles work to achieve this by changing the dimensions of the thoracic cavity.

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| Name = Muscles of respiration

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| Image = Respiratory system.svg

| Caption = Muscles of the body's respiration

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The '''muscles of respiration''' are the [[muscle]]s that contribute to [[inhalation]] and [[exhalation]], by aiding in the expansion and contraction of the [[thoracic cavity]]. The [[Thoracic diaphragm|diaphragm]] and, to a lesser extent, the [[intercostal muscle]]s drive respiration during [[breathing|quiet breathing]]. The elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.

==Principal and Accessory Muscles of Inspiration==

There are two main groups of inspiratory muscles: principal and accessory. Principal muscles are used regardless of the level of breathing required, while accessory muscles are only used during forced breathing. For example, during heavy exercise and because of some respiratory conditions such as Asthma. <br> <br>

==Diaphragm==

The principal muscles are the [[External intercostal muscles|external intercostal]], the intercondral part of the internal intercostal muscles, and the diaphragm. Both the external intercostal muscles and the intercondral elevate the ribs, thus increasing the width of the thoracic cavity, while the diaphragm contracts to increase the vertical dimensions of the thoracic cavity, and also aids in the elevation of the lower ribs. <br><br>

{{Main|Thoracic diaphragm}}

The [[Thoracic diaphragm|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 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 [[lung]]s. 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.<ref name="Mechanics of respiratory muscles">{{cite journal|last1=Ratnovsky|first1=Anat|title=Mechanics of respiratory muscles|journal=Respiratory Physiology and Neurobiology|date=2008|volume=163|issue=1–3|pages=82–89|pmid=18583200|doi=10.1016/j.resp.2008.04.019|s2cid=207505401}}</ref>

The diaphragm is also involved in non-respiratory functions, helping to expel [[vomiting|vomit]], [[faeces]], and [[urine]] from the body by increasing intra-abdominal pressure, and preventing [[acid reflux]] by exerting pressure on the [[esophagus]] as it passes through the [[esophageal hiatus]].

==The intercostalIntercostal muscles==

The accessory muscles of inspiration are: The [[sternocleidomastoid]] (elevated sternum) and the [[scalene]] muscles (anterior, middle and posterior scalene).<ref> Netter FH. Atlas of Human Anatomy 3rd ed. Icon Learning Systems. Teterboro, New Jersey 2003 - plate 191 </ref> After heavy exercise, people will often lay down with their hands fixed. This has a similar effect to fixing the insertion of the accessory muscles, and thus when the muscles contract, the origin (the upper ribs and/or the sternum) is pulled to aid respiration

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. The [[external intercostal muscles]] are most important in respiration. These have fibres that are angled obliquely downward and forward from rib to rib.<ref name="BarrettBarman2009">{{cite book|author1=Kim E. Barrett|author2=Susan M. Barman|author3=Scott Boitano|author4=Heddwen Brooks|title=Ganong's Review of Medical Physiology, 23rd Edition|url=https://books.google.com/books?id=k2eVn40wVb8C|date=24 July 2009|publisher=McGraw-Hill Companies,Incorporated|isbn=978-0-07-160567-0|chapter=35. Pulmonary Function}}</ref> The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the [[rib cage]], assisting in inhalation.

==MusclesAccessory muscles of Expirationrespiration==

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 of [[respiratory distress]].<ref>{{cite web|last1=Bass|first1=Pat|title=Signs of Respiratory Distress in Children|url=http://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=90&ContentID=P02960|website=University of Rochester Medical Center|access-date=11 May 2015}}</ref> There is no definitive list of accessory muscles, but the [[sternocleidomastoid]] and the [[Scalene muscles|scalenes]] (anterior, middle, and posterior) are typically included, as they assist in elevating the rib cage.<ref>Netter FH. Atlas of Human Anatomy 3rd ed. Icon Learning Systems. Teterboro, New Jersey 2003 - plate 191</ref> 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.<ref name="Raper, A. J. 1966">Raper, A. J., Thompson, W. T., Shapiro, W., & Patterson, J. L. (1966). Scalene and sternomastoid muscle function. Journal of Applied Physiology, 21, 497-502.</ref> With an increase in the respiratory volume, sternocleidomastoids also become active.<ref name="Campbell, E. J. M. 1955">Campbell, E. J. M. (1955). The role of the scalene and sternomastoid muscles in breathing in normal subjects. An electromyographic study. Journal of Anatomy, 89, 378.</ref> Both muscles are simultaneously activated when one breathes in at the maximal flow rate.<ref name="Raper, A. J. 1966"/>

During quiet breathing, there is little to no muscle contraction/relaxation involved. This process is simply done by the elastic recoil of the lungs and the rib cage. <br><br>

Apart from the above neck muscles, the following muscles have also been observed contributing to respiration: [[Serratus anterior muscle|serratus anterior]], [[pectoralis major]] and [[pectoralis minor]], [[trapezius]], [[Latissimus dorsi muscle|latissimus dorsi]], [[Erector spinae muscles|erector spinae]], [[iliocostalis]], [[Quadratus lumborum muscle|quadratus lumborum]], [[Serratus posterior superior muscle|serratus posterior superior]], [[Serratus posterior inferior muscle|serratus posterior inferior]], [[Levatores costarum muscles|levatores costarum]], [[Transversus thoracis muscle|transversus thoracis]], [[Subclavius muscle|subclavius]] (Kendall et al., 2005). The [[levator labii superioris alaeque nasi muscle]] lifts the [[Human nose#External nose|sides of the nostrils]].

During active breathing, the internal intercostals, with the exception of the intercondral, and the abdominal muscles ([[rectus abdominis]], [[external oblique|external]], [[internal oblique]] and [[transversus abdominis]]) pull the thoracic cage in and force air out of the lungs.<ref> Netter FH. Atlas of Human Anatomy 3rd ed. Icon Learning Systems. Teterboro, New Jersey 2003 - plate 191 </ref> <br>

==Muscles of exhalation==

==The intercostal muscles==

During quiet breathing, there is little or no muscle contraction involved in exhalation; this process is simply driven by the [[Elastic recoil|elastic recoil of the lungs]]. When forceful exhalation is required, or when the elasticity of the lungs is reduced (as in [[Pneumatosis#Lungs|emphysema]]), active exhalation can be achieved by contraction of the abdominal wall muscles ([[rectus abdominis]], [[transverse abdominis]], [[external oblique muscle]] and [[internal oblique muscle]]). These press the abdominal organs cranially (upward) into the diaphragm, reducing the volume of the thoracic cavity.<ref name="Mechanics of respiratory muscles"/>

The [[internal intercostal muscles]] have fibres that are angled obliquely downward and backward from rib to rib.<ref name="BarrettBarman2009"/> These muscles can therefore assist in lowering the rib cage, adding force to exhalation.<ref name="Mechanics of respiratory muscles"/>

Along with the [[diaphragm]], the intercostal muscles are one of the most important groups of respiratory muscles. These muscles are attached between each rib and are important in manipulating the width of the thoracic cage. There are three layers of intercostal muscles.<br><br>

==References==

The external intercostal have fibres that go forward and downward. These fibres are called the antero-inferior, and are sometimes referred to as the front pocket muscle since the fibres mimic the direction a hand would enter a front pocket. The antero-inferior fibres have the effect of lifting up the ribs during contraction. Anteriorly, the external intercostal muscles do not directly attach to the sternum, but are replaced by the anterior intercostal membrane. <br><br>

{{Reflist}}

==Further reading==

The internal intercostal also have fibres, which go backward and upward. These are called the postero-superior, or the back pocket muscles. The last layer is the innermost intercostals and consists of three separate parts; the subcostal (posteriorly), the innermost intercostal (laterally, which often causes confusion with the innermost intercostal referring to all twenty groups) and the transversus thoracis (anteriorly). The innermost intercostal muscles are also "back pocket" muscles. The internal and innermost intercostals have the opposite effect of the external intercostals and aid in forced expiration. The internal intercostal is replaced by the posterior intercostal membrane posteriorly.

* Kendall, F., McCreary, E., Provance, P., Rodgers, M., Romai, W. (2005). '''Muscles testing and function with posture and pain (5th ed.)'''. PA, USA: Lippincott Williams & Wilkins.

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==References==

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[[Category:Respiration]]

[[Category:Respiration]]

[[pt:Músculos da respiração]]