Why do we cry while chopping
onions?
The tears you shed when chopping
onions aren't emotional ones. That leaves two other categories of tears: basal
and reflexive. Basal tears are the ones that hang around our eyes and eyelids
to act as a lubricant so that leaves us with the final option: reflex
tears. The lachrymal glands above the eyelids regulate the release
of tears. In the case of reflex crying, an external irritant, such as dust or
smoke, triggers nerve endings in the cornea to communicate with the brain stem. The brain registers the
irritation in the eye then alerts the lachrymal gland to stimulate tear
production to flush away the invader. Since
onions are part of the plant genus Allium they absorb sulfur in the earth,
which helps form a class of volatile organic molecules called amino
acid sulfoxides. These sulfoxides trigger tears when onions are
chopped. As we chop up an onion, it releases lachrymatory-factor synthase enzymes. These catalysts cause
the chemical chain reaction that ends with you tearing up. These enzymes react with the
sulfoxides and convert them into sulfenic acid. Sulfenic acids are highly
unstable and rearrange into a compound called syn-propanethial-S-oxide. When syn-propanethial-S-oxide enters
the air around our faces and approaches our eyes, it evokes the reflexive tear response. Multiple nerve endings in the
cornea register the sensation of the syn-propanethial-S-oxide as a substance
that could harm our eyes, therefore the brain stem phones the lachrymal glands
and the tears commence.
Friendly
tip:
Chew gum
while you chop onions! J
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