Editing Inhalation (section)

== Mechanism ==
Inhalation begins with the contraction of the muscles attached to the rib cage; this causes an expansion in the chest cavity.  Then takes place the onset of contraction of the [[thoracic diaphragm]], which results in expansion of the [[intrapleural space]] and an increase in negative pressure according to [[Boyle's law]].  This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus. 

The inflow of air into the lungs occurs via the [[respiratory airways]]. In health, these airways [[Obligate nasal breathing|begin with the nose]].<ref name=cc>{{cite web
|url=https://health.clevelandclinic.org/breathe-mouth-nose/
|title=Should You Breathe Through Your Mouth or Your Nose?
|access-date=2020-06-28
|last=Turowski
|first=Jason
|date=2016-04-29
|publisher=[[Cleveland Clinic]]
}}</ref><ref name="guardian">{{cite web|title=Your Nose, the Guardian of Your Lungs|url=https://www.bmc.org/otolaryngology-head-neck-surgery/resources/your-nose-guardian-your-lungs|access-date=2020-06-29|publisher=[[Boston Medical Center]]}}</ref> It is possible to begin with the mouth, which is the backup breathing system. However, chronic [[mouth breathing]] leads to, or is a sign of, illness, and it does not have mucus in the mouth to trap the unwanted substance unlike the nostrils<ref name=harmful>{{cite web
|url=https://www.nbcnews.com/healthmain/mouth-breathing-gross-harmful-your-health-1C6437430
|title='Mouth-breathing' gross, harmful to your health
|access-date=2020-06-28
|last=Dahl
|first=Melissa
|date=2011-01-11
|publisher=NBC News
}}</ref><ref name="role">{{cite web
|url=https://www.journal-imab-bg.org/issues-2018/issue1/JofIMAB-2018-24-1p1878-1882.pdf
|title=THE ROLE OF MOUTH BREATHING ON DENTITION DEVELOPMENT AND FORMATION
|access-date=2020-05-31
|last=Valcheva
|first=Zornitsa
|date=January 2018
|publisher=Journal of IMAB
}}</ref><ref name="nesnpr">{{cite web
|url=https://www.npr.org/transcripts/862963172
|title=How The 'Lost Art' Of Breathing Can Impact Sleep And Resilience
|access-date=2020-06-23
|last=Gross
|first=Terry
|date=2020-05-27
|publisher=[[NPR|National Public Radio (NPR)]]/[[Fresh Air]]
}}</ref> They end in the microscopic dead-end sacs([[Pulmonary alveolus|alveoli]]) always opened, though the diameters of the various sections can be changed by the [[Sympathetic nervous system|sympathetic]] and [[parasympathetic nervous system]]s. The alveolar air pressure is therefore always close to atmospheric air pressure (about 100&nbsp;[[Pascal (unit)|kPa]] at sea level) at rest, with the pressure gradients that cause air to move in and out of the lungs during breathing rarely exceeding 2–3&nbsp;kPa.<ref name="Chrisvan L 1995">{{cite journal |last1=Koen |first1=Chrisvan L. |last2=Koeslag |first2=Johan H. | title=On the stability of subatmospheric intrapleural and intracranial pressures |journal= News in Physiological Sciences | date=1995 |volume=10 |issue=4 |pages=176–178 |doi=10.1152/physiologyonline.1995.10.4.176}}</ref><ref name="Williams & Wilkins">{{cite book |last1=West |first1=J.B. |title=Respiratory physiology: the essentials. |location=Baltimore |publisher=Williams & Wilkins |date=1985| pages= 21–30, 84–84, 98–101 }}</ref>

Other muscles that can be involved in inhalation include:<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 4/4ch2/s4ch2_10 |chapter-url=http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section4/4ch2/s4ch2_10.htm|archive-date=2016-03-24}}</ref>
* [[External intercostal muscles]]
* [[Scalene muscles]]
* [[Sternocleidomastoid muscle]]
* [[Trapezius muscle]]