在线国产一区二区_成人黄色片在线观看_国产成人免费_日韩精品免费在线视频_亚洲精品美女久久_欧美一级免费在线观看

您現在的位置: > Language Tips > Easy English > Odd Question  
 





  Why do we yawn?
[ 2006-05-15 10:27 ]

Almost everyone yawns when they feel sleepy. So do most animals.But we don't completely understand why people and animals for that matter, yawn.

It's widely assumed that yawning occurs because we are tired or bored or because we see someone else doing it, but there isn't any hard evidence to support these beliefs.

Scientists do not purport to know all of the biological mechanisms of the yawn, but tend to agree that a yawn is an involuntary respiratory reflex, which regulates the carbon dioxide and oxygen levels in the blood.

Technically, a yawn is the reflex opening of the mouth followed by the deep inhalation and slow exhalation of oxygen.

The very act of yawning is but one of a number of involuntary reflexes controlled by the spinal and nerve centers.

Scientists speculate that the onset of a yawn is triggered either by fatigue, or by sheer boredom as, at those times, breathing is shallow, and little oxygen is carried to the lungs by the oxygen-toting cardiovascular system.

When one yawns, his or her alertness is heightened, as the sudden intake of oxygen increases the heart rate, rids the lungs and the bloodstream of the carbon dioxide buildup, and forces oxygen through blood vessels in the brain, while restoring normal breathing and ventilating the lungs.

This quite plausible theory of yawning falls short of explaining many aspects of yawning. Scientists explain away the "contagious" nature of yawning, that is when one person's yawn triggers another nearby to yawn, as due to the power of suggestion, but are at a loss when attempting to explain why yawning occurs excessively in patients with lower brainstem damage or with multiple sclerosis.

Other unlocked mysteries include why fetuses in the womb yawn, when it is a well-known fact that they do not intake oxygen into their lungs until after live birth, or why individuals with high concentrations of oxygen in their blood streams yawn.

Until these questions are answered, do not assume that a person who yawns in your presence is bored with what you are saying, or suffers from exhaustion. Simply be pleased that he or she is not bored to death.

 

note:

 

 

 

 

 

purport: 聲稱
involuntary: 不知不覺的
respiratory reflex: 呼吸反射

inhalation: 吸入
exhalation: 呼出


spinal
: 脊椎的

 

 

cardiovascular system: 心血管系統

 

 

 

falls short of: 不足以,達不到


at a loss: 困惑的

brainstem: 腦干
sclerosis: 硬化癥

fetus: 胎兒
womb: 子宮

 
 
 




主站蜘蛛池模板: 免费国产一区 | 国精日本亚洲欧州国产中文久久 | 欧美一区二区在线免费观看 | 激情一区| 99视频久久 | 日韩精品一区二区三区中文在线 | 中文字幕在线视频观看 | 日韩精品视频免费专区在线播放 | 国产欧美精品一区二区三区四区 | 欧美 日韩 在线播放 | 中文字幕日韩一区二区 | 理论片91| 蜜桃视频日韩 | 久久一级 | 精品视频在线观看一区二区 | 国产精品国产三级国产aⅴ中文 | 日韩欧美一区二区在线观看 | 园产精品久久久久久久7电影 | 日韩一区电影 | aa级毛片毛片免费观看久 | 黄频免费在线观看 | 中文字幕自拍偷拍 | 男女福利 | 狠狠视频 | 一区二区三区国产 | 国产精品一区二区久久久久 | 91短视频版在线观看免费大全 | 日日网| 超碰美女 | 精品久久99 | 亚洲精品成人 | 美女一级黄 | 日韩成人影院 | 精品久久久久一区二区国产 | 最近最新中文字幕 | 97精品在线| 中文字幕成人 | 精品视频免费 | 黄a免费网站 | 在线视频亚洲 | 国产一区二区三区在线 |