MadSci Network: Neuroscience |
Dear No Name, No School, etc., You ask about how big a particle need be to stimulate a sneeze when it gets onto the mucus membranes of your nose. This is an interesting question. First because it presumes that the nose is a transducer of mechanical stimuli and second because it presumes that there must be threshold to trigger a response. Actually, neither of these are probably correct. The mucus membranes of the nose trap fairly large particles without triggering a sneeze....at least before the specific properties of the particle begin to stimulate an inflammatory or irritant reaction. It is the irritation and inflammation induced by the particle that stimulates the sneeze, not the particle itself. Pollens, house dust, and other particles are usually harmless, but when they irritate the nose the body responds by expelling them from the nasal passages. We breath in pollen grains all the time without sneezing. However, if the pollen you breathed in the past stimulated an allergic immune response; and, you have IgE antibodies against the pollen or dust antigens, then the next time that species of pollen touches your nasal mucus membranes it will trigger a cascade of immune reactions culminating in activating mast cell secretion. The cytokines (drug like hormones) and histamine released by these mast cells will cause quick swelling and increased mucus secretion in your nose and Hacchhoooo you will sneeze. But, the sneeze will have been caused by this reaction to the pollen, not by the size or weight of the pollen grain. The nose mistakes strong odors, sudden chills, and even bright lights (see photic sneeze reflex) for parasites, and it tries to defend itself with a sneeze. None of these stimuli are particles yet they too stimulate sneezing either because the chemicals in strong odors or sudden chills directly irritate, or the bright lights stimulate a neurological reflex that results in a sneeze. It always amazes me that the speed of air coming out of the nose or mouth during a sneeze is over 100 miles per hour and the force is usually sufficient to expel pretty big bits of mucus, help drain plugged paranasal sinuses, and shoot out a parasitic worm if it happens to have crawled into your nose. Johnny Carson used to talk of the bird of paradise flying up a nose but he was just being silly....I think. Here are some other answers about what triggers a sneeze. http: //www.madsci.org/posts/archives/sep99/938695934.Gb.r.html http://www.people. virginia.edu/~rjh9u/sneeze.html
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