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: 一区二区日韩 | 久久精品伊人网 | 亚洲国产精品久久久 | 亚洲国产精品久久久久秋霞蜜臀 | 91免费精品国偷自产在线在线 | 99热官网| 国产亚洲视频在线 | 国产福利在线免费 | 日本亚洲欧美 | 国产成人福利视频在线观看 | 日本无码V视频一区二区 | 噜噜噜噜狠狠狠7777视频 | 色呦呦在线看 | 午夜精品久久久久久久久久久久久 | 日韩在线视频导航 | 成人tv| 欧美成年性h版影视中文字幕 | 夜夜狠狠操 | 久久3| 97色免费视频 | 国产精品揄拍100视频最近 | 97在线观看视频 | 91大神精品长腿在线观看网站 | 色在线视频网站 | 99精品一区二区 | 99精品在线免费观看 | 五月天激情视频 | a级毛片免费高清视频 | 看黄网站在线看 | 亚洲精品国产偷自在线观看 | 2018天天干夜夜操 | 免费观看一级特黄欧美大片 | 亚洲免费网站 | 黄色av网站在线免费观看 | 国产精品爱久久久久久久 | 精品啪啪 | 亚洲综合99 | 亚洲一区二区中文字幕 | 国产中文字幕在线观看 | 国产一区二区三区在线视频 | 欧美国产二区 |