Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, January 19, 1995 TAG: 9501190061
SECTION: EXTRA PAGE: 1 EDITION: METRO
SOURCE: JOEL ACHENBACH
DATELINE: LENGTH: Medium
A: First we should report a fact you may not know: When a mosquito sucks your blood, she gets so bloated that it is hard for her to fly away. What does she do? Right. She gets rid of some ballast. A little urination action. We tell you this only so that you can get really mad the next time you're bitten.
Now then: An itch is hard to define. It's kind of like pain. But it doesn't hurt. It's just bothersome, sometimes intensely so. It sends a signal to your brain saying: Scratch me. In fact that is pretty much the scientific definition of an itch.
``Itch evokes a desire to scratch. Whereas pain hurts,'' says Robert LaMotte, a Yale neurobiologist who is an expert of the physiology of itching. Unlike an itch, a pain ``evokes an avoidance reaction. You try to avoid touching the part that hurts.''
Itching can be caused by many things, like a rash, a bite, a serious metabolic illness like kidney disease, or even a light pricking by a researcher wielding a piano wire. For a long time people thought an itch was just a modified form of pain, perhaps some lesser version of it. LaMotte rejects that idea.
An itch, he notes, can be intense, even debilitating. It's clearly a different type of sensation with its own physiological mechanics.
He has studied nerves up close. What he's found is that there are many different types of stimulation-registering nerve fibers, called nociceptors. Some nociceptors respond to painful stimuli. Others respond to both pain and itch-producing stimuli. But the itch signal has its own pathway through the spinal cord. ``Those nociceptors that respond to itch are connected to an itch-producing circuit in the central nervous system,'' he says.
If an itchy stimulus is joined by a painful stimulus, the itch will disappear, because the itch signal is blocked or repressed by the pain. And that's why you scratch. You scratch yourself to create enough pain to overwhelm that itchy feeling.
If you have a little poison ivy inflammation, you can aim a blow dryer at it, just enough heat to hurt a bit without actually burning yourself, and the itch will go away.
The strange thing is that itching has been largely ignored by the scientific community. That's not because it's not a serious issue. The problem is that you can't interview animals. You can't ask them if something hurts or itches.
``It's a subjective sensation that's hard to measure in experimental animals,'' says LaMotte.
In any case we don't really like the idea of scientists doing things to make animals feel itchy. That seems a bit diabolical. But if they have to do such experiments, we know exactly which species most deserves to be the test subject. Yeah. Dang skeeters.
|n n| The Mailbag: Someone in Michigan who ``feels stupid'' and doesn't want her name used writes, ``I plug a cord into an electric wall outlet and it runs my hair dryer. When I pull the cord out, the dryer stops. If I touch the prongs of the cord after it's pulled out I don't get a shock. Where did the electricity go that was in the cord?''
Dear Feels Stupid: Don't worry, there's no such thing as a stupid question - though if there were, yours would be a strong candidate. Actually you are onto something most people don't realize. There is a little static electricity in the cord even after it's unplugged. The charge is too slight to notice. ``It's infinitesimally small,'' promises Steve Taylor, an electrical engineer with Pepco, the Washington-area electric utility.
Electricity goes into the cord through one prong of the plug and exits back into the wall from the other. The moment you pull out the cord you've cut off the flow of current. It's a bit like what happens with the hose in your backyard. Turn off the water and you might have a little bit of water in the hose for a moment but your water pressure will dissipate. Electricity needs current to get any work done. Otherwise those electrons almost instantly lose their motivation and start scattering.
``A lamp cord just has the type of construction that it won't hold much of a charge. There's just not much metal there,'' says Taylor.
But when electrical workers do something on a high-voltage power line, even after they turn off the juice they have to be careful. There's enough static electricity to hurt someone. So they'll ground the line, using a stick or some other instrument.
Now that you know this, you can stop horsing around with electrical appliances. It's making us nervous.
Washington Post Writers Group
by CNB