When we wake up, why do we have crust in our eyes? - S.S.
“Eye crusts” are the leftover protein and fat from tears that have dried up. Tears have three components:
- Salty water, which comes from the tear gland behind the upper outer corner of our eye.
- Protein, secreted by the conjuctiva, which is the clear film that covers the eye.
- And fat, which comes from ducts in the eyelids.
Tears
do lots of jobs. They clean the eye. They fill in tiny imperfections in
the surface of the cornea, which needs to be perfectly smooth for
maximal vision. They also deliver nutrients to the cornea, which has to
be clear to let light through to the iris, and therefore has no blood
vessels to deliver a “food supply.” And of course tears flow at times
of emotion, when the tear glands power up and produce more salt water.
At
night, with our eyes closed and protected, we don’t display emotion,
and with our eyes closed we don’t get dirt in our eyes. So we don’t
make tears. Small amounts of the mixture already on the surface of the
eye seep out, but without a fresh supply of liquid from the tear gland,
the fat and protein dry up.
Why does your breath smell so bad when you wake up? - S.B. and A.B.
This
one ought to get you to brush before you go to bed. That smell is …
bacteria gas. Gross, but accurate. There are lots of bacteria in our
mouth all the time, feeding on the tiny leftover bits of what we’ve
eaten. Ever hear of plaque, the stuff all those toothpaste ads promise
to get rid of? Plaque is nothing more than organized colonies of
bacteria chowing down on food bits on your teeth.
When
we’re awake, some plaque is removed when we chew, talk, drink, even
when we breathe. But overnight, when those disturbances in the mouth
stop, it’s party time for the bacterial colonies on your teeth, and
they multiply like crazy. Their waste products are acids, which cause
cavities, and gases, which cause that rude blast of morning breath.
Why do we snore? - S.D.
To bug the person sleeping next to us, of course.
Actually, there are several causes of snoring. All of them have something to do with restriction of the upper airway.
So
if you try to sleep next to an overweight elderly drunk with a
misshapen jaw and a cold who’s taking muscle relaxants … bring
industrial-strength earplugs.
Why is yawning contagious? - P.H.
If you don’t think YAWNING is contagious, see if you YAWN by the time you’re done reading this explanation of YAWNING.
First,
let’s dispel a myth. You don’t yawn to take in extra oxygen. “That’s
been rejected in lab tests,” says YAWN expert Robert Provine, professor
of psychology at the University of Maryland’s Baltimore County campus.
He had test subjects breathe air with extra oxygen. For others, he
reduced the oxygen intake by giving them air high in carbon dioxide.
Neither caused more or less YAWNING.
(YAWN. YAWN. YAWN.)
Provine
says “we YAWN when we’re changing states of activity. Going from sleep
to wakefulness, like YAWNING in the morning. Or wakefulness to sleep.”
(He says we YAWN more in the morning when we wake up, by the way.)
“Concert
pianists will YAWN before going out to an important performance.
Olympic athletes YAWN before the big event. Embryos begin YAWNING
eleven weeks after conception,” Provine notes. He says YAWNING is
somehow connected to changing levels of body activity, changes from one
state to another, like inactive to active or vice versa, but nobody
understands just what the connection is.
“It
probably helps stir up the blood and brain chemistry to facilitate
those transitions from one level of activity to another.”
Why?
“YAWNING is ancient and autonomic,” Provine says. “Maybe it’s to get
everyone in the tribe to synchronize their states of activity, to
increase the success of the tribe if everyone’s working together. We
really don’t know.”
(YAWN. YAWN. YAWN.)
YAWNING
is highly contagious, he says. Every vertebrate species YAWNS. Fish
YAWN. Birds YAWN. Alligators YAWN. But Provine says it’s apparently
only contagious in humans.
Provine
has made test subjects YAWN by showing them a YAWNING face.
Interestingly, if he shows them just the YAWNING mouth, it doesn’t
trigger the YAWNING. If he covers the mouth, and shows them just the
nose and eyes of the YAWNING face, it does. He’s made subjects YAWN by
talking about YAWNING, or asking the test subjects to think about
YAWNING, or by having them read about YAWNING.
Yawning yet?
Alan
Boyle is msnbc.com’s science editor. David Ropeik is a risk
communication consultant who provided information for this report in
2000.
