SneezingLike burping and farting, sneezing is simply one of those necessities that can take one by surprise in a variety of awkward situations -- at rest or at work, or even in the throes of passion. Yet just as mankind has long pondered the cause and mechanism of orgasm, so has it sought to explain the mystery of the sneeze. To most modern sneezers, it seems obvious that the primary function of the sneeze is to expel offending particles from the upper resperatory system, a cleansing mechanism. Likewise, ancient sneezers considered that the true function was to drive out evil spirits which had invaded the body -- more or less the same thing.
The sneeze occurs when the nerve endings of the mucous membrane of the nose are irritated. This irritation then stimulates your trigeminal nerve, sending impulses through the trigeminal ganglion to a set of neurons located in the brainstem that collectively are termed the "sneezing center". These neurons send new impulses along the facial nerve back to the nasal passages and the face, causing the nasal passages to secrete fluid and become congested. The eyes may also tear. At the same time, the "sneezing center" also sends impulses to your respiratory muscles via the spinal cord. It is these impulses that create the deep inbreath and forceful outbreath, or the paroxysm of the sneeze itself.
Meanwhile, the impulses travelling through the facial nerve happen to stimulate nerves which govern the reflex response we call the the blink. So, essentially, one message is sent, but two listeners receive it, and act on it. Hence the sneeze blink.
Compare the "photic sneeze reflex," more commonly known as "sun sneezing", that strange phenomenon where people sneeze when suddenly exposed to bright light. Recognized in medical journals for the last 40 years, it has also been called the "ACHOO syndrome". Supposedly only 25% of the population is prone to sun sneezing, leading some to speculate that the tendency to sneeze at the sun may be an inheritable trait that only some possess. (It should be noted however that most newborns exhibit sun sneezing.)
In 1888 the famous patent grabber Thomas Edison was quickly flipping through sequential pictures of someone sneezing when he realized that he could make a picture appear to move by showing a bunch of still shots in quick succession. So he assigned W.K.L. Dickson, one of his many assistants, to the task of inventing the necessary devices to record moving images (the "Kinetograph") and to play them back (the "Kinetoscope"). Edison and Dickson's discoveries launched a technological chain of invention that led to the cinema and all that supplanted it.