Q: Really? How does that happen?

　　A: The body has a natural protective mechanism called the fight-or-flight response, which was originally described by Walter Cannon [chairman of Harvard University's physiology department from 1906 to 1942]。 If, in the wild, an animal is faced with a life-threatening situation, the autonomic (involuntary) nervous system responds by increasing heart rate, increasing blood flow to the muscles, dilating the pupils, and slowing digestion, among other things. All of this increases the chances of succeeding in a fight or running away from, say, an aggressive jaguar. This process certainly would be of help to primitive humans, but the problem, of course, is that in the modern world there is very limited advantage of the fight-or-flight response. There is a downside to revving up your nervous system like this.

　　问：真的吗？那是怎样发生的？

　　答：身体有个自然保护机制，叫做“斗争还是逃避”反应，Walter Cannon（他从1906年至1942年间任哈佛大学生理学系主任）首先描述了这个反应。如果动物在野外遇到危及生命的情景，这个自动（无意识的）神经系统会做出响应，这时心跳加快、肌血增多、瞳孔放大、消化减慢以及伴随其它种种反应。所有这些反应都增大了在危险面前（比如美洲豹的进攻）无论是斗争还是逃跑的成功机会。但是对于人来说，神经系统的这种反应有负面作用。

　　Q: How can the fight-or-flight response lead to death?

　　A: The autonomic nervous system uses the hormone adrenaline, a neurotransmitter, or chemical messenger, to send signals to various parts of the body to activate the fight-or-flight response. This chemical is toxic in large amounts; it damages the visceral (internal) organs such as the heart, lungs, liver and kidneys. It is believed that almost all sudden deaths are caused by damage to the heart. There is almost no other organ that would fail so fast as to cause sudden death. Kidney failure, liver failure, those things don't kill you suddenly.

　　问：“斗争还是逃避”反应怎么会导致死亡？

　　答：这套自动神经系统利用肾上腺激素（一种神经递质，或者称为化学信使）把信号发送到身体的各个部分，以便激活“斗争还是逃避”反应。大量的肾上腺激素是有害的；它会损坏内脏器官，比如心脏、肺、肝脏和肾、人们认为几乎所有的突然死亡都是由于心脏受损所致。几乎没有其它的器官像心脏那样衰竭如此之快，以至于导致突然死亡。肾脏衰竭、肝脏衰竭是不会突然致死的。

　　Q: What exactly happens in the heart when it's flooded with too much adrenaline?

　　A: Adrenaline from the nervous system lands on receptors of cardiac myocytes (heart-muscle cells)， and this causes calcium channels in the membranes of those cells to open. Calcium ions rush into the heart cells and this causes the heart muscle to contract. If it's a massive overwhelming storm of adrenaline, calcium keeps pouring into the cells and the muscle just can't relax.

　　There is this specially adapted system of muscle and nerve tissue in the heart—the sinoatrial (SA) node, the atrioventricular node, and the Purkinje fibers—which sets the rhythm of the heart. If this system is overwhelmed with adrenaline, the heart can go into abnormal rhythms that are not compatible with life. If one of those is triggered, you will drop dead.

　　问：当过量的肾上腺激素涌入心脏的时候，心脏中到底发生了什么情况？

　　答：来自神经系统的肾上腺激素“着陆”到心脏肌细胞的受体，这使得这些肌细胞的膜中的钙通道打开。钙离子涌入到心脏细胞，导致心肌收缩。如果是大量的肾上腺激素涌入心脏，那么钙离子就会持续不断地涌入，从而导致心肌连续收缩，得不到休息。

　　心脏中有一套由肌肉和神经组织构成的特殊体系，它们控制着心脏的节奏。这个体系由窦房结、房室结和浦金氏纤维（Purkinje fibers）组成。如果这个体系中的肾上腺激素大大过量，那么心跳就会不正常，生命就会危险。如果这个体系中的某一项被过量肾上腺激素激活，人就会死亡。