Basic Biology question - why can I breathe through only my nose even when my mouth is open?
Asked by
MrItty (
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August 13th, 2009
As I understand basic human anatomy (and granted, most of what I know comes from my 11th grade Biology class), the act of breathing has nothing to do with the nose or mouth. Instead, when you consciouslessly tell yourself to breathe, you are in fact flexing your diaphragm muscle. This has the effect of either bringing air into the body or expelling it out.
Under that system though, it would seem that on an inhale, the air would travel from the outside world into the lungs through whatever orifices are available. That is, if the mouth is open, air should go in via both mouth and nose. Similarly for exhaling, air should exit via both.
Yet that’s clearly not what happens in real life. You can choose whether to breath through your nose or your mouth, even when both are open and unplugged. What is the mechanism that determines that? Is there a “switchback” somewhere near where the two passages combine? If so, what is it called?
Thanks!
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8 Answers
Look at this diagram. What you’re describing is what happens when you use the rear portion of your tongue (the large hump in the diagram) to block that gap between the area marked “epiglottis” and the area marked “tonsils”. This effectively seals off the mouth’s gateway to the respiratory tract.
This mechanism enables you to eat without swallowing air and to breathe (when you have foor or liquid in your mouth) without aspirasting non-air into your lungs. It is implicated in sleep apnea (when the passage to the lungs i inappropriately closed off) and in the the fact that, when you are under general anaesthesia, the anaesthesiologist is charged with your not aspirating refluxes, such as vomit.
@Harp : what is the mechanism for sealing off only the entryway to the digestive tract?
@Harp, okay that makes sense… but that would seem to take of only the first half. That is, depending on the positioning of the tounge, I can block off air to/from my mouth. But I’m equally able to breathe only through my mouth, even when my nose is unplugged. So it seems like there should be another mechanism to close off that passage as well, no?
There are other reasons for breathing through the nose rather than the mouth. You nose has cilia and mucous membranes that are designed to filter out foreign objects, pollen, etc. before it reaches the lungs.
Yoga breathing is always through the nose.
“The hairs in the nose filter out dust and dirt particles that the mouth and throat cannot; however there is another reason (pertinent to yoga) why nose breathing is done. Yoga has traditionally taught that breathing through the nose better maintains the correct balance of oxygen and carbon dioxide in the blood. Mouth-breathing expels carbon dioxide far too quickly, restricting the oxygen in the blood and, consequently, the brain. This can result in being tense, irritable and anxious.”
@MrItty To close off the nose and leave the mouth passage open, you use the muscles of your soft palate. In this diagram, they’re the little numbered muscles. They pull the flap of the soft palate (in yellow) up to seal the passage to the nose.
Just guessing here… but even if you maintained perfect manual control of the epiglottal and soft palate muscles and were able to keep them all open at the same time, I’d still think that your mouth offers the path of least resistance for getting air in.
The difference in resistance between both airways is, I expect, somewhat large. Your nostrils alone are only a fraction of the size of your open mouth… let alone the more complicated path through the nasal passages.
Here’s an experiment. Open your mouth only fractionally and inhale. Try to focus on getting air in both through your nose and mouth. I can make it happen… but my mouth is only very slightly open when I do.
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