Question: why do we hiccup? I know it's when your diaphragm has a spasm. But i don't see why it does so.

Emma Trantham answered on 25 Jun 2012:

This is a really interesting question and I confess I had to go look it up because I couldn’t remember all of the details!

You’re right that a hiccup is a spasm of the diaphragm muscle. As you’ll know if you’ve had them, hiccups are involuntary, which means we don’t have conscious control over them.

The muscle spasms because a reflex arc has been triggered: something is sensed by a type of detector and a signal is sent up a nerve to the spinal column where it is transferred to another nerve. This signal is then sent back down that second nerve to activate the diaphragm muscle. (It’s called a reflex arc because the signal only passes through the spinal cord and doesn’t go up to the brain.)

There are many different things that can stimulate and set off this reflex arc including eating or drinking (esp, if done quickly), alcohol, stress/excitement. There are also some diseases that can cause long term hiccuping (where you can be hiccuping for days or weeks without stopping. In fact one poor person once hiccuped for 60 years!!!)

Why we evolved to hiccup is another question. A couple of theories have been proposed. Some scientists think that when babies hiccup in the womb it helps them develop and exercise the muscles that they will need to use for breathing after they are born. A bit like a gym routine for the unborn baby! Some scientists think that hiccups may have developed as a mechanism of clearing air from the stomach of baby animals that suckle on their mum’s breast milk. (They often gulp down air at the same time as milk which can fill up their stomachs so they don’t drink enough milk, and can make them feel uncomfortable. This is why any of you with younger brothers/sisters/cousins etc. may have seen someone ‘burp’ them after feeding them.) Both of these ideas tie into the fact that hiccups are more common in children than adults.

Oh and a final trivia point – the medical term for hiccups is ‘singultus’

Hope this has answered your question 🙂