Why do we Hiccup?

What causes hiccups? Doctors point out that a round of hiccups often follows from stimuli that stretch the stomach, like swallowing air, or too rapid eating or drinking.
Others associate hiccups with intense emotions, or our response to them: laughing, sobbing, anxiety, and excitement.

Let’s look at what happens when we hiccup.
It begins with an involuntary spasm or sudden contraction of the diaphragm, the large dome-shaped muscle below our lungs that we use to inhale air.  This is followed almost immediately by the sudden closure of the vocal cords and the opening between them, which is called the glottis.

The movement of the diaphragm initiates a sudden intake of air, but the closure of the vocal cords stops it from entering the windpipe and reaching the lungs. It also creates the characteristic sound– ‘hic’
The medical term for hiccups is known as “singultus.”

To date, there is no known function for hiccups; they don’t seem to provide any medical or physiological advantage.  Why begin to inhale air, only to suddenly stop it from actually entering the lungs?

In a 2003 study, a group of scientists led by Christian Straus proposed that hiccups are a hangover from our evolutionary past. Straus et al. suggest that hiccups originate from our amphibian ancestors. The evidence they point to is between the mechanism of hiccups in humans and the breathing method of amphibians such as frogs.

The contraction of the diaphragm and closure of the glottis allowed “primitive air breathers” that still possessed gills to breath. This is similar to many modern amphibians, where the mysterious spasm that many of us find annoying is actually vital in amphibians to push water across their gills and stop water getting into the lungs.

In the study, researchers suggest that while we no longer have our frog-like breathing abilities, the brain circuitry controlling gill ventilation is still conserved in mammals today. Straus et al. point to other similarities between hiccupping and gill ventilation in animals like tadpoles as further evidence for their theory. The frequency of gill breathing in tadpoles is reduced by increased CO2 concentration and an increase in C02 is thought to decrease the frequency of hiccups, which is why some people recommend breathing in and out of a paper bag.Watch TED-Ed Lesson Why do we hiccup? - John Cameronhttp://ed.ted.com/lessons/why-do-we-hiccup-john-Cameron

Study:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3504071/#b2
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