What Causes Hiccups?
So now you know what they are, but what causes hiccups? The actual causes are many and varied and the medical community has not reached a consensus on exactly why they happen. It used to be thought that the diaphragm itself was the cause. Later, research showed that it was not the diaphragm, but was most commonly caused by distension and expansion of the stomach, a disease or irritation of the thorax, or irritation to the phrenic nerves. Expansion of the stomach occurs when too much air enters the stomach. This can lead to acid reflux or stomach acid being pushed into the esophagus. Hiccups may be the body's attempt to protect itself from this. The phrenic nerve is a nerve that extends from the throat region of the spine down through the diaphragm. These nerves (the body has a right and left phrenic nerve) are responsible for some sensation in the chest but, much more importantly, are the brain's main connection to the diaphragm and are responsible for telling the diaphragm when to contract and relax. Without the phrenic nerves, we would not be able to breathe. Irritation to the phrenic nerve can cause it to tell the diaphragm to contract when its not meant to, leading to hiccups. In addition, there is some evidence that irritation to the Vagus Nerve (a nerve extending from the neck and running throughout the chest) can also cause hiccups.
There is a phylogenetic (evolutionary) hypothesis with some supporting evidence that states that hiccups are an evolutionary remnant in our systems from nearly 400 million years ago. Many amphibians exhibit a behavior that is similar to, but different from, hiccupping. Amphibians have this reflex in order to keep water out of their lungs when breathing through their gills. The hypothesis is that our hiccupping is a vestigial remnant of this reflex in our amphibian ancestors. We may have held on to the reflex because hiccupping can be useful to babies for keeping the milk out of their lungs when breastfeeding. This hypothesis is closely related to yet another which asserts that we have a 'central pattern generator' - a neuronal circuit - responsible for the set of actions that occur while hiccupping. The associated study showed that hiccupping is a more complex reaction than previously thought, involving the diaphragm, mouth, tongue, and even causing a slowed heart rate.
In the end, there is no general consensus on, medically, what causes hiccups. Regardless of the medical cause, however, they may be brought on by any of the following hiccup causes:
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