Sneezing, or sternutation, is an abrupt, involuntary and forceful expulsion of air through the nose and mouth. This involuntary reflex, triggered by the trigeminal nerve, is the body's attempt to clear an irritant, such as dust, pollen or viruses, from the nose.
The Science Behind Sneezing
The mechanics of sneezing is a sophisticated process involving the nervous system and various muscle groups. Sensory nerves within the lining of the nasal cavity, known as the nasal mucosa, are stimulated by an irritant and send an electrical signal through the trigeminal nerve to the medulla oblongata, or lower brainstem.
This, in turn, prompts the brainstem to quickly command the diaphragm, chest, and vocal cords to contract in unison. The complex physiological events ensure that the irritant is rapidly ejected from the respiratory system.
The Anatomy of a Sneeze
A sneeze occurs in the blink of an eye, but it consists of four phases:
Irritation: A foreign particle or chemical enters the nasal passage and stimulates the local nerve endings.
Transmission: The trigeminal nerve relays an "all hands on deck" message to the brain's "sneeze center".
Inhalation: The brain tells the body to take a deep inhalation, causing the lungs to fill.
Exhalation: The glottis (space between the vocal cords) shuts to increase pressure, and then opens to allow a sudden expulsion of air, saliva and mucus via a strong contraction of the diaphragm and abdominal muscles.
What Triggers a Sneeze?
Although all sneezes are the same, what triggers them may be very different.
Sneeze Trigger: Allergens
Description : Pollen, dander, and mold
Biological Purpose : Expels proteins that the body mistakenly thinks are harmful.
Sneeze Trigger: Irritants
Description : Dust, black pepper, smoke and strong perfumes.
Biological Purpose : Mechanically removes irritants from your nose.
Sneeze Trigger: Infections
Description : The common cold, influenza and rhinoviruses.
Biological Purpose : Removes excess mucous from the body's immune response to a virus
The Photic Sneeze Reflex or Sun Sneezing
Have you ever come out of a dark movie theatre and into the sunlight and sneezed? This is known as the photic sneeze reflex. According to genetic studies, 18-35% of the population is affected by this phenomenon. The medical term for this is ACHOO syndrome (Autosomal Dominant Compelling Helio-Ophthalmic Outburst).
Researchers theorize that this is caused when the signal from the optic nerve, which narrows the pupils in response to bright light, "crosses the wires" with the nearby trigeminal nerve, resulting in the brain thinking your nose is being irritated.
Why do we shut our eyes when we sneeze?
Sneezing with your eyes shut is an autonomic reflex. Once the brain decides to sneeze, it will send a signal to the muscles of the respiratory system to contract, but it will also send a signal to the muscles around the eyes to close.
Is it possible to sneeze with your eyes open?
Although it is very hard to do because of the autonomic nature of the reflex, some people can indeed sneeze with their eyes open. This will not make your eyes pop out of the socket, contrary to the popular myth.
How fast is a sneeze?
One study showed that air can be expelled at a speed of 35 to 100 miles per hour during a forceful sneeze. In addition, studies suggest that a sneeze can release as many as 100,000 mucous particles into the air.
Can you sneeze while you are sleeping?
You can't sneeze while you are in the deep stages of sleep. During the Rapid Eye Movement stage of sleep, the body's muscles are paralysed and the nerve reflexes that cause you to sneeze are inhibited.
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