I. Match the headings A-F to the suitable parts of the text 51 to 55. There is one extra heading. A. Two types of stress. B. The fallout of cell death. C. How stress can be useful D. One reason behind bad tempers. E. Regrowing the brain with exercises. F. The best type of exercise. 51. Despite its bad reputation, stress historically had a vital role to play. Commonly referred to as the fight or flight mode, the sudden release of stress hormones like adrenalin and cortisol causes the heart to beat faster, airways to dilate and blood vessels to open up, all of which push the body towards optimal performance and, ultimately, survival. 52. In ordinary modern life, although were in little danger of being stalked by wild beasts down city streets, our bodies react to stress in the same ways. Experiencing anxiety, fear and stress is considered a normal part of life when it is occasional and temporary, such as feeling anxious and stressed before an exam or a job interview. It is when these acute reactions are prolonged or cannot be switched off, however, that serious physical, social and cognitive issues can result. 53. Of major concern is the impact on the brain. Researchers have found that the hippocampus, the control centre of memory and our ability to learn, can physically shrink in response to prolonged release of stress hormones like cortisol which result from chronic stress. 54. While this part of the brain gets smaller, another area, the amygdala, which is involved in processing emotions, can grow with chronic stress. Across species, a larger amygdala has been found to correlate with aggression and this, coupled with the weakened connection to the prefrontal cortex, the brains decision-making centre, can profoundly impact mood and behavior. 55. In the past, it was accepted that there was a limited number of neurons in the brain and as they died off as a result of ageing, stress or substance abuse, for instance, they were lost forever. It turns out, however, that this is not the case and that stem cells within the brain are actually able to create new neurons. In other words, lost neurons can be replaced. làm giúp mik, ai làm đầu vote 5 sao