Editing Exhalation (section)

===Involuntary expiration===

Involuntary respiration is controlled by respiratory centers within the medulla oblongata and pons. The medullary respiratory center can be subdivided into anterior and posterior portions. They are called the ventral and dorsal respiratory groups respectively. The [[pontine respiratory group]] consists of two parts: the [[pneumotaxic center]] and the [[apneustic center]].<ref name="Article #3" />  All four of these centers are located in the brainstem and work together to control involuntary respiration. In our case, the [[ventral respiratory group]] (VRG) controls involuntary exhalation.{{citation needed|date=June 2022}}

The neurological pathway for involuntary respiration is called the bulbospinal pathway. It is also referred to as the descending respiratory pathway.<ref name="Article #3" />  "The pathway descends along the spinal ventralateral column. The descending tract for autonomic inspiration is located laterally, and the tract for autonomic expiration is located ventrally."<ref name="Article #2">{{cite journal |doi=10.1113/expphysiol.2008.042424 |pmid=18487316 |title=Breathing rhythms and emotions |journal=Experimental Physiology |volume=93 |issue=9 |pages=1011–21 |year=2008 |last1=Homma |first1=Ikuo |last2=Masaoka |first2=Yuri |s2cid=2686895 |doi-access=free }}</ref>  Autonomic Inspiration is controlled by the pontine respiratory center and both medullary respiratory centers. In our case, the VRG controls autonomic exhalation. Signals from the VRG are sent along the spinal cord to several nerves. These nerves include the intercostals, phrenic, and abdominals.<ref name="Article #3" />  These nerves lead to the specific muscles they control.  The bulbospinal pathway descending from the VRG allows the respiratory centers to control muscle relaxation, which leads to exhalation.{{citation needed|date=June 2022}}

====Yawning====

[[Yawning]] is considered a non-respiratory gas movement.  A non-respiratory gas movement is another process that moves air in and out of the lungs that do not include breathing. Yawning is a reflex that tends to disrupt the normal breathing rhythm and is believed to be contagious as well.<ref name="yawning primary">{{cite journal |doi=10.1080/09515080802513292 |title=Content and Contagion in Yawning |journal=Philosophical Psychology |volume=21 |issue=6 |pages=721–37 |year=2008 |last1=Sarnecki |first1=John |s2cid=144972289 }}</ref>  The reason why we yawn is unknown. A common belief is that yawns are a way to regulate the body's levels of O<sub>2</sub> and CO<sub>2,</sub> but studies done in a controlled environment with different levels of O<sub>2</sub> and CO<sub>2</sub> have disproved that hypothesis.  Although there is not a concrete explanation as to why we yawn, others think people exhale as a cooling mechanism for our brains.  Studies on animals have supported this idea and it is possible humans could be linked to it as well.<ref name=Yawning>{{cite journal |doi=10.3389/fnevo.2011.00007 |pmid=22319494 |title=Changes in Physiology before, during, and after Yawning |journal=Frontiers in Evolutionary Neuroscience |volume=3 |pages=7 |year=2012 |last1=Corey |first1=Timothy P. |last2=Shoup-Knox |first2=Melanie L. |last3=Gordis |first3=Elana B. |last4=Gallup |first4=Gordon G. |pmc=3251816 |doi-access=free }}</ref> What is known is that yawning does ventilate all the alveoli in the lungs.{{citation needed|date=June 2022}}

====Receptors====

Several receptor groups in the body regulate metabolic breathing. These receptors signal the [[respiratory center]] to initiate inhalation or exhalation. [[Peripheral chemoreceptors]] are located in the aorta and carotid arteries. They respond to changing blood levels of oxygen, carbon dioxide, and [[Hydron (chemistry)|H<sup>+</sup>]] by signaling the pons and medulla.<ref name="Article #3" />  Irritant and stretch receptors in the lungs can directly cause exhalation. Both sense foreign particles and promote spontaneous coughing. They are also known as mechanoreceptors because they recognize physical changes not chemical changes.<ref name="Article #3" />  [[Central chemoreceptors]] in the medulla also recognize chemical variations in H<sup>+</sup>. Specifically, they monitor pH change within the medullary interstitial fluid and cerebral spinal fluid.<ref name="Article #3" />