The Body's Response
The best way to envision the effect of acute stress is to imagine yourself in a primitive situation, such as being chased by a bear.
The Brain's Response to Acute Stress
In response to seeing the bear, a part of the brain called the hypothalamic-pituitary-adrenal (HPA) system is activated.
Release of Steroid Hormones and the Stress Hormone Cortisol. The HPA systems trigger the production and release of steroid hormones (glucocorticoids), including the primary stress hormone cortisol. Cortisol is very important in organizing systems throughout the body (including the heart, lungs, circulation, metabolism, immune systems, and skin) to deal quickly with the bear.
Release of Catecholamines. The HPA system also releases certain neurotransmitters (chemical messengers) called catecholamines, particularly those known as dopamine, norepinephrine, and epinephrine (also called adrenaline).
Catecholamines activate an area inside the brain called the amygdala, which appears to trigger an emotional response to a stressful event. In the case of the bear, this emotion is most likely fear.
Release of Neuropeptide S. The brain releases neuropeptide S, a small protein that modulates stress by decreasing sleep and increasing alertness and a sense of anxiety. This gives the person a sense of urgency to run away from the bear.
Effects on Long- and Short-Term Memory. During the stressful event, catecholamines also suppress activity in areas at the front of the brain concerned with short-term memory, concentration, inhibition, and rational thought. This sequence of mental events allows a person to react quickly, either to fight the bear or to flee from it. It also interferes with the ability to handle difficult social or intellectual tasks and behaviors during that time.
At the same time, neurotransmitters signal the hippocampus (a nearby area in the brain) to store the emotionally loaded experience in long-term memory. In primitive times, this brain action would have been essential for survival, because long-lasting memories of dangerous stimuli (such as the large bear) would be critical for avoiding such threats in the future.
Research also finds that during times of stress, nerve cells in the brain interpret chemical signals incorrectly. Instead of switching "off," these nerve cells perceive the signals as telling them to switch "on." It's as though the brain's "brakes" fail in response to stress.
Response by the Heart, Lungs, and Circulation to Acute Stress
Review Date: 10/14/2010
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.