The SNEEZE.

The other night, Sci was drifting slowly off to sleep.  Suddenly, I sneezed.  It woke me up completely again, and left me wondering, with some irritation, whether it couldn't have waited til I was asleep and didn't care.

And then I thought: CAN you sneeze in your sleep? I asked the Twitterverse and looked around in vain. There are conflicting reports. I may not ever have my answer.

But dang did I ever learn a lot about sneezing. And of course, when that happens...I gotta blog it. So today's post is going to be a basic science post (SCIENCE! 101) on the SNEEZE. How it works, what causes it, and...whether you can do it in your sleep.

Songu and Cingi. "Sneeze reflex: facts and fiction" Therapeutic Advances in Respiratory Disease, 2009.

(Props go out to Songu and Cingi, who have written what may very well be one of the most entertaining reviews I have EVER read. I highly recommend).

Is there anything better than sneezing kittens?

Maybe sneezing baby elephants.

The sneeze (the medical term is "steternation") is a respiratory reflex, a series of stereotyped movements which follow from each other in their entirety. Once you complete the inhale portion of a sneeze, you're going to complete the rest of it, the only thing you can control is how loudly and where it goes.

A sneeze can be divided into two sections, the sensitive phase, and the efferent (outward) or respiratory phase. The sensitive phase is the stimulation in your nose, the tickle that says that something is coming. This is the point at which you can try to stop it with a finger under your nose or something and you may very well be successful. The tickling sensation in your nose is the result of stimulation of the trigeminal nerve. This is the 5th cranial nerve (out of 12, I really HAVE to do a post or 12 on the cranial nerves some day...always so much to blog!), and it extends out and innervates the skin of your face, including the delicate mucosa inside your nose.

(That's your trigeminal nerve. All over your FACE. Source)

The trigeminal nerve sections inside your nose end in sensitive receptors. Some of these are sensitive to chemicals (think capsaicin), while others are sensitive to mechanical stimuli (which would be a physical particle like dust mechanically pressing against the receptor). When you get something in your nose or something stimulates the trigeminal nerve, the signals travel up toward the brain and hit the lateral medulla.

(look where the white arrow is pointing. Source)

This area is a sneezing center for you brain, and when stimulated enough, will trigger the reflexive response of a sneeze. If you have enough of a tickle in your nose, the lateral medulla will reach threshold, and send signals out to the lungs, eyes, and throat. And you get the following sequence.

1) Your eyes close (if your eyes don't close during a sneeze, you may not be going through the full stereotyped series, and this can be an indication in a patient that sneezing is the result of a psychiatric issue rather than a physical one).

2) You breathe in DEEP.

3) Your glottis (a series of fleshy folds in your throat) closes.

4) You breathe out explosively, building up pressure in the lungs, the glottis flashes open in response. Air exists rapidly through the mouth and nose.

ACHOOOOO.

5) You recover and start feeling around somewhat desperately for a kleenex.

There are lots of different causes of sneezing. The most common are things like the common cold and allergies (rhinitis), and the photic sneeze reflex (called ACHOO syndrome, which I have blogged about before, and which is sneezing in response to sudden exposure to bright light). But there are other, less well known causes of sneezing, some of which are pretty amazing.

- physical stimulation of the trigeminal nerve: this can be a feather, dust up your nose, or a good whiff of capsaicin.

- central nervous system pathologies. The big one here is called lateral medullary syndrome. Sneezing isn't a symptom here, it's actually a cause! The onset of LMS has been associated with a massive onset of sneezing, which can shear the vertebral artery and prevent blood from getting to the lateral medulla, causing a whole hose of very unpleasant symptoms, one of which is that the person CANNOT sneeze following that initial outburst. Other pathologies which can have sneezing as part of their symptoms include types of epilepsy, where sometimes sneezing can predict the onset of a seizure.

- psychogenic sneezing: this is the type of sneezing I mentioned before, where someone sneezes and sneezes and cannot appear to stop, but the sneezes are small, and the eyes often stay open. These sneezing fits (a case report of one was 2 months in duration) respond best to talk and behavioral therapy.

- snatiation reflex: this is a fun one! This is a rare condition in which people sneeze when their stomachs are FULL. "Snatiation" is apparently the combination of "sneeze" and "satiation", and otherwise stands for the acronym "Sneezing noncontrollably at a tune of indulgence of the appetite- a train inherited and ordained to be named" aka "medical students really need to find better ways to amuse themselves". It's extremely rare, but really does happen.

- sneezing at sexual ideation or orgasm. This was a totally new one to me. With regard to noses and orgasm, the only thing I've ever seen before is that characters in Japanese anime shows seem to get nosebleeds when they think sexy thoughts (would love to know the physiological basis behind that one).

This is, of course, completely mythical. But there ARE people who SNEEZE when exposed to sexy thoughts. It's pretty rare, but sneezing and sexual excitement has been documented since the 19th century. People used to think that maybe this was because both erections and sneezes were the results of blood flowing to "erectile tissue" in the penis and nose respectively, but now we just don't know. There are case reports both of people sneezing immediately following orgasm, as well as reports of people who sneeze merely at the thought of hotness. It's very rare, but if this DOES happen to you, I think you might want to keep it to yourself, otherwise every time you sneeze your friends will look at you funny.

But there is one important thing about sneezing. You know how your mother or friends told you not to hold in your sneezes because your face would explode or something (I was told my eyes would pop out)? Well, your eyes won't pop out and your face won't explode. But the pressure involved in a sneeze IS up to 176mmHg IF you are closing your nose. And that's a bit. It's enough to cause damage to things like your hearing and your eyes, and even caused a woman with osteoporosis to break her nose. So let your sneeze fly proud!

And now we come to the final question: CAN you sneeze in your sleep? Well, I still don't know. But here's how I think of it.

Concepts FOR sneezing in your sleep: it's a reflex and should occur automatically, though it might then wake you up.

Concepts AGAINST sneezing in your sleep: there's a condition that most people enter in to when asleep wherein you lose most of your muscle tone (this happens in non-REM sleep, it's not sleep paralysis, that's different). This might prevent you from sneezing, and might be a GOOD thing, because then you won't, you know, accidentally bite your tongue in half or something.

So, does anyone know which it is? And can give me a citation? Sci's gotta have DATA. My current hypothesis is that we probably CAN sneeze in our sleep, and the muscle tone relaxation prevents us from biting our tongues in half anyway, but what do I know?

But for now, Sci's going to sleep. Hope I don't sneeze.

Songu, M., & Cingi, C. (2009). Sneeze reflex: facts and fiction Therapeutic Advances in Respiratory Disease, 3 (3), 131-141 DOI: 10.1177/1753465809340571