日韩精品久久一区二区三区_亚洲色图p_亚洲综合在线最大成人_国产中出在线观看_日韩免费_亚洲综合在线一区

您現(xiàn)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(tǒng)

 

 

 

falls short of: 不足以,達(dá)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: 日韩在线视频观看 | 国产剧情一区二区三区 | 色多多成视频人在线观看 | 一个色综合网 | 超碰欧美 | 久久精片 | 日韩中文字幕在线观看视频 | 一级做a爰片性色毛片中国 日本黄色免费片 | 那一个欧美一级毛片 | 毛片网此| 九色网址| 欧美精品福利 | 国产精品视频在线播放 | 国产苐1页影院草草影院 | 日韩一级片在线免费观看 | 亚洲欧美中文在线观看4 | 欧美极品一区二区 | 欧美大片在线播放 | 国产成人黄网址在线视频 | 97精品国产综合久久 | 无码免费人妻A片AAA毛 | 99久久精品国产一区二区成人 | 亚洲日本va在线视频观看 | 香蕉久草 | 婷婷色国产偷v国产偷v小说 | 国产午夜精品一区二区三区在线观看 | 久色一区 | 国产一区在线播放 | 三级毛片在线 | 成人二区 | 日韩欧美一区二区三区免费观看 | 色黄视频网站 | 好大好硬好长好爽a网站 | 久福利| 久草国产视频 | 黄色免费观看 | 韩漫重考生漫画画免费读漫画下拉式土豪漫 | 97骚碰| 99在线观看 | 国产人成| 日本激情视频一区二区三区 |