The parasympathetic nervous system acts like a brake. It triggers the fight-or-flight response, providing the body with a burst of energy so that it can respond to perceived dangers. The sympathetic nervous system functions like a gas pedal in a car. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. This area of the brain communicates with the rest of the body through the autonomic nervous system, which controls such involuntary body functions as breathing, blood pressure, heartbeat, and the dilation or constriction of key blood vessels and small airways in the lungs called bronchioles. The hypothalamus is a bit like a command center. This area of the brain functions like a command center, communicating with the rest of the body through the nervous system so that the person has the energy to fight or flee. When someone experiences a stressful event, the amygdala, an area of the brain that contributes to emotional processing, sends a distress signal to the hypothalamus. When it perceives danger, it instantly sends a distress signal to the hypothalamus. The amygdala interprets the images and sounds. When someone confronts an oncoming car or other danger, the eyes or ears (or both) send the information to the amygdala, an area of the brain that contributes to emotional processing. The stress response begins in the brain (see illustration).
More preliminary research suggests that chronic stress may also contribute to obesity, both through direct mechanisms (causing people to eat more) or indirectly (decreasing sleep and exercise).
Research suggests that chronic stress contributes to high blood pressure, promotes the formation of artery-clogging deposits, and causes brain changes that may contribute to anxiety, depression, and addiction. Over time, repeated activation of the stress response takes a toll on the body. Over the years, researchers have learned not only how and why these reactions occur, but have also gained insight into the long-term effects chronic stress has on physical and psychological health. Unfortunately, the body can also overreact to stressors that are not life-threatening, such as traffic jams, work pressure, and family difficulties. The carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses helps someone to fight the threat off or flee to safety. This combination of reactions to stress is also known as the "fight-or-flight" response because it evolved as a survival mechanism, enabling people and other mammals to react quickly to life-threatening situations. A stressful incident can make the heart pound and breathing quicken.
Chronic activation of this survival mechanism impairs healthĪ stressful situation - whether something environmental, such as a looming work deadline, or psychological, such as persistent worry about losing a job - can trigger a cascade of stress hormones that produce well-orchestrated physiological changes.
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