「用進廢退」的大腦 "Disuse" of the brain

「用進廢退」的大腦 圖三 「用進廢退」是生物學中一個普遍的規律，人們早已有深刻的認識。但是，長期以來，科學家對於人進入老年以後，大腦功能是否繼續服膺它，卻有疑慮，因為一般認為中央神經系統的細胞，成年以後，不能新生或再生。這是筆者在60年前在學校學習神經生理學時公認的法則。但是，近一、二十年來，由於觀察手段的精進，有越來越多的證據顯示，成年人的中樞神經系統的細胞衰亡後也可以再生。近來有報導，提出了足以令人信服的證據，指出司掌學習新技術功能的大腦，至少在實驗的小鼠中，成年以後是可以新生的。 圖三顯示一個神經細胞，用來體現學習過程在細胞的水平上，是怎樣完成的。這些細胞構成神經活動的基本元素，因此又叫作神經元。它有一個細胞核，從細胞的四壁長出無數的小樹狀突，其功能是從別的神經元接受傳給它的資訊。這種資訊以電位元改變的形式傳來後，神經元作出反應。通過軸突，傳遞到下一個神經元的樹狀突或另一類細胞，如肌肉細胞，按其指示作出反應。這就構成基本的神經通路。 如圖所示，樹狀突短而多，軸突卻長而只有一條。為了使信息的傳達不受干擾，軸突四周由一層像電線外皮的髓鞘包繞起來。髓鞘也向長長的軸突提供保養，不必依靠已甩在老遠的「老家」運來。學習一門新技術時，必需開通很多以前從來沒有的新通路。為此，神經元就要長出更多的樹狀突。學得多，樹狀突就多。不學習，樹狀突就少。長久不學習，原有的樹狀突就消失了。我們可以設想，一個學有專長的教授，或者能作高難度的雜技演員，其大腦某些特定地區的神經元，一定有比一般人濃密得多的樹狀突。這種設想已在近年來，得到實驗的啟示，甚至證明。 ／劉鍾毅 2008-11-09 "Disuse" of the brain Figure III "Disuse" Biology is a general rule, people have been profound. However, for a long time for scientists to enter old age, the brain function of whether or not to continue to subscribe to it, there are doubts as is generally believed that the central nervous system cells, adult, not new or renewable. This is the author of 60 years ago in school learning neural recognized when Physiology law. However, the last one, over the past 20 years, as a means of observation to improve, more and more evidence that the adult central nervous system cells after the decline and fall can also be renewable. Recent reports have put forward a convincing enough evidence to charge the Secretary pointed out that learning new techniques of brain function, at least in the experimental mice, after the adult is the new-born. Figure III shows that a nerve cell to reflect the learning process in the cell level, what is completed. These nerve cells constitute the basic elements, it also called neurons. It has a nucleus from the cell walls of countless small tree growing process, and its function is to receive from other neurons to its information. This information to potential changes in the form of yuan came after the neurons respond. Through the axon, passing to the next neuron or another type of dendritic cells, muscle cells, such as in accordance with their instructions to respond. This constitutes a basic neural pathway. As shown, dendritic short, but long axons and there is only one. In order to convey information without interference, from around the axons skin layer of the myelin-like wire wrapping up. Myelin sheath axon long to provide maintenance, do not have to rely on have thrown away the "home", to. A study of new technologies, the need has never been opened, many of the new access road. To this end, it is necessary to grow neurons more dendritic. Learn much more on the dendritic. Do not study, dendritic less. Not for a long time to learn, the original dendritic disappeared. We can imagine that a learned professor, or can be difficult for the acrobat, and its specific areas of the brain neurons, there will be much more dense than the average person's dendritic. This vision has been in recent years, the experiment has been the inspiration, or even to prove. / Liu Zhong 2008-11-09 View more information, see the World Journal reported that e-ePaper

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