What do you do when your diaphragm involuntarily contracts?
And the answer: hiccup.
According to the Mayo Clinic, the diaphragm is "the muscle that separates your chest from your abdomen and plays an important role in breathing. This involuntary contraction [or reflex] causes your vocal cords to close very briefly, which produces the characteristic sound of a hiccup."
Hiccups can occur from any range of activities – from laughing too much, to drinking too quickly to even just feeling fear. Even fetuses (inside the womb!) can hiccup. But why, exactly?
Scientists still aren't exactly sure. What they do know is that the act of hiccuping is a response which travels along the phrenic nerve up to the brain stem. Once it reaches the brain, it processes the signal and sends one back down to make the diaphragm contract, creating a reflex arc. Hiccups, then, are momentarily stuck in a signal-response pattern that triggers a contraction of the diaphragm involuntarily.
To date, there is no known function for hiccups. They don't provide any medical or physiological advantage; in fact, hiccups actually stop the short intake of air before it can really reach your lungs. Physiological mechanisms with no apparent purpose such as hiccups create a challenge for scientists. Is there a function that hasn't yet been discovered, or perhaps none at all? One theory posits that the act is a relic left over from ancient evolutionary processes, long before humans were around. When creatures in the sea began to evolve to land, their gills became the gradual evolution to lungs (similar to the process of a frog's maturation). As such, the hiccup could have been an inhalation to move water over the gills but prevent it from filling the lungs.
What do you think? Are hiccups an evolved trait, or just a side effect? Learn more about hiccups below.