Final answer:
When the brain perceives a life-threatening situation, it triggers the fight-or-flight response, which prepares the body to confront or escape the threat through hormonal changes and physiological arousal.
Step-by-step explanation:
When the brain recognizes a situation as potentially life-threatening, it initiates a cascade of physiological responses known as the fight-or-flight response. This response is mediated by the amygdala and the hypothalamus within the limbic system of the brain. Once a threat is detected, adrenal glands release hormones such as adrenaline and cortisol, leading to increased heart rate, dilated pupils, elevated blood pressure, and a state of high alertness. This physiological reaction prepares the body to either confront the danger or escape from it as quickly as possible.
In the modern world, the fight-or-flight response can be triggered by psychological threats as well. While these reactions were critical for survival against predators in the past, today's stressors, like giving a presentation or taking a test, can cause the same response, potentially leading to negative health outcomes if endured repeatedly. Chronic exposure to stress can contribute to heart disease and weakened immune system function due to the constant activation of this response to non-physical threats.