英語聽力文摘 疼痛感受器
Hey! and then…Ouch!
傷害性刺激作用于末梢神經(jīng)引起神經(jīng)興奮電活動(dòng)，沿著脊髓傳人神經(jīng)纖維中的細(xì)纖維(A和c纖維)傳人脊髓，進(jìn)而引起痛覺。痛覺是由于痛覺感受器受刺激而誘發(fā)的，其他感受器受到刺激產(chǎn)生相應(yīng)的感覺，并非痛覺。人體內(nèi)痛覺的傳導(dǎo)依賴于機(jī)體受刺激側(cè)對(duì)側(cè)脊髓前外側(cè)1/4象限內(nèi)上行神經(jīng)纖維構(gòu)成的傳導(dǎo)束的功能完整性。先天Jf生痛覺缺如的起因與痛覺相關(guān)的脊髓傳人神經(jīng)纖維的缺乏有關(guān)。參與痛覺產(chǎn)生的高級(jí)神經(jīng)中樞為丘腦和大腦皮質(zhì)，這些部位的損傷可以引起痛覺減弱。
'Hey! and then…Ouch!' on this Moment of Science.
One thing we don’t want anyone to do is poke themselves with a sharp object after reading this Moment of Science. But the next time you accidentally get poked you might notice something interesting.
Say you reach into a pile of clothes where a needle is sticking up. If you are able to reflect for a moment as you are sucking your fingertip, you may realize that you have had two separate sensations.
The first of these is what we might think of as the “hey!” sensation. It conveys the information that something startling has happened to your finger, and that thing is unpleasant. A moment after that comes a deeper-down feeling of pain. This latter sensation might be called the “ouch!” It’s not startling so much as just plain bad.
What’s going on here?
In fact, there are several different kinds of fibers that send pain information to your brain. These are called “nociceptors,” and they respond not only to pins but to heat, cold, chemical changes, and other dangers. These receptors send their information through two different kinds of fibers: the large, fast “A” fibers, and the smaller, slower “C” fibers.
Because they are naturally coated with a conductive substance, “A” fibers transmit messages at about 330 feet per second, whereas “C” fibers can only handle about six-and-one-half feet per second.
The delay some people can distinguish between “Hey!” and “Ouch!” is thought to be due to this time lag. It also makes sense that the faster “A” fibers would be the ones whose job it is to get you to pull your finger away right now.
