Why Do We Shiver When Cold?
Your body needs to keep a core temperature of about 98.6°F (36.9°C). To prevent hypothermia and other consequences of a chilled core, your brain monitors temperature very closely.
If the surface of your skin gets too chilly, skin receptors send signals to the brain, which sets into motion a series of warming tricks .
Shivering is one such tactic, in which your muscles contract and expand in speedy bursts. In addition to quaky limbs, your jaw muscles might begin to shiver, making your teeth chatter.
This twitching exercise produces heat, which helps to raise body temperature. It's also your signal to find a toasty haven and a warm drink .
Why Is Yawning Contagious?
I won't take offense if this article makes you look a bit sleepy. Just reading about yawns can — wait for it — induce one without warning. And it’s not because your brain needs oxygen, whatever the schoolyard myth.
Some current theories focus on yawning as a social cue (like laughing) that communicates information and helps organize group behavior. By passing from person to person with unconscious ease, a yawn can convey some piece of information (perhaps "I’m tired", or "this opera is dull") around a social circle. Such a tool would have come in handy in pre-language days. But does the science back this up?
One 2005 study scanned the brains of people watching yawns, and located unique activity patterns in brain areas related to behavioral mimicry. So next time you get a dirty look for yawning in a meeting, chalk it up to caveman communication.
Why Do My Eyes Close When I Sneeze?
Ah, the elusive achoo — there's much mystery surrounding our sternutation reflex, a.k.a. the sneeze.
Sneezing protects our nasal passageways from foreign particles by forcing a 100 mph whoosh of air from the lungs, but the reflex demands more movement than that. When stimulated, the brain stem’s sneeze center orders muscle contraction from esophagus to sphincter. That includes the muscles controlling your eyelids. Some sneezers even shed a few tears.
No one knows why. It's possible the body has grown to associate protecting the nasal passageways with protecting the eye, or it may just be a result of our body’s wiring. Nor do scientists know why some people sneeze at bright lights, or why the reflex is pleasurable to some but not others. Whatever its workings, the sneeze has the distinction of being the only reflex that warrants a "bless you" from total strangers.
Why Do We Sleep?
We spend roughly a third of our lives asleep. Snoozing is vital to our well-being — no human can go without it for more than a handful of days. And yet it is perhaps the least understood of all our activities.
Theories abound, but much of our need for sleep remains a mystery. Sleep certainly allows for a lot of body "maintenance work," from production of chemicals that get used during waking hours to the self-organization of neurons in the developing brain. REM sleep, with its high neuronal activity, occurs more during periods of brain growth.
Several theories point to sleep as a state vital to memory and learning abilities. Sleep may help ingrain episodic memories into long-term storage, and it also may simply give our waking activities a much-needed break.
Why Do We Snore?
The beastly sound of snoring can awaken even the heaviest sleeper. Your slumber pal isn't trying to stir you on purpose.
As you fall asleep, the muscles that keep your breathing passage open begin to relax, while your throat contracts. The tightening throat means a snug journey for passing air. For some people, this narrowing causes air to push forcefully through the throat, disturbing the relaxed muscle tissues in the back of the throat, causing them to vibrate. The vibrating tissue produces the sound familiarly known as snoring.
Some common causes: propping your head up too high with pillows, allergies leading to mucus in your throat, and obesity.
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