The Stress Response
Anxiety, fear, and other powerful emotions can signal the sympathetic nervous division of the ANS to elicit the stress response. As a result blood flow to skeletal muscles is increased and endocrine gland activity is adjusted. (1) To repeat again, the only two pathways of the stress response are the HPA axis and the SAM axis. Once these routes are activated, a myriad of neuroendocrine changes are launched.
This consists of elevated levels of hormones and proteins such as EPI, NEPI, renin, calcitonin, cortisol, thyroxine, parathyroid hormone, gastrin, insulin, erythropietin. All of them will be discussed in forthcoming posts. Another result of the stress response is increases in blood pressure, heart rate, galvanic (sweating) skin response, blood glucose levels, coagulation time and muscle tension. (2) These reaction of the body to stress are absolutely necessary for survival, but if perpetuated excessively, these modifications could lead to heightened physiologic and emotional retort and immunosuppresion. People undergoing chronic stress and the resulting chronic physiologic hyperactivity do exhibit and increased probability of disease and premature death.
Chronically stressed persons often show increased muscle tension, decreased peripheral skin temperatures, and a frenzied response to an acute stressor. The individuals have a hard time returning to the hypoactive (relaxation) state. The assertion of a stress response is typically gauged by measurements of SNS responses, such as blood pressure, heart rate, sweat rate, peripheral skin temperature.(3)
It is possible to bring about stress physiologically and psychologically. Maybe an illustration is necessary. A result of psychologic stress can be compromised immune activity and illness. A disease (physiologic) could result into a psychologic stressor such as fear, anxiety, guilt etc., which further diminishes the body's ability to regain its strength.
Lets revisit our rock climber Theresa for a step by step explanation of stress response.
Theresa was rock climbing in an area that was indigenous to rattlesnakes. She was careful to wear protective leg gear so she would be safe while she climbed to the top of the bluff. She reached a particularly precarious part of the climb with only one good handhold left, and she was very tired. With as much force as possible, Theresa jammed her fingers into the rock crevice and prepared to swing herself up to the top. At that moment, she heard a rattling sound. In an instant, she was gripped with fear.
Here is what was literally going on in her head in the blink of an eye.(4)
The limbic system and the amygdala made a quick connection between her fear fear of snakes and her current situation. In a fraction of a second, the image of being bitten several times, the fear of pain, her hand swelling, and the fear of an excruciating death was consolidated, and this image was accepted by the hypothalamus.
The hypothalamus responded by secreting CRH via the HPA axis, which signaled the pituitary gland to release ACTH, thereby stimulating the adrenal glands to pour cortisol into her body.
Simultaneously, the SNS via the SAM pathway triggered the release of EPI, NEPI, and other neurotransmitters and neuropeptides, preparing Theresa for the struggle of her life.
Her heart raced, her breathing became rapid, her blood pressure jumped, and she began to sweat profusely. Her pupils dilated, and her body stiffened as her gaze froze on a shadow in the crevice. Her thoughts focused, as a laser, on her predicament.
The prefrontal cortex had been simultaneously stimulated assessing the danger and preparing for a decision. (7) "Don't let go!" is the message she had screaming in her head. She may survive the snake bite, but she never would survive a 2000-foot fall. With all her will, Theresa strengthened her finger grip on the crevice and with tremendous effort swung herself to the top of the bluff. She ripped off her climbing glove and checked for signs of a bite. Her hand was unblemished. She was safe, and her bodily responses slowly returned to a more normal state.
Did this experience have an immediate effect on Theresa's physiologic and biochemical reactions? Certainly. Will this experience have a permanent effect on her health? Probably not. However, long-term stress of considerably less intensity can affect health and longevity. A one time acute stressor event of short duration is potentially harmful only for individuals with severely compromised immune systems or severely degraded health. The pathways are, nonetheless, the same.
Next: Chemical Messengers
1. Siegman A. Paraverbal Correlates of Stress: Implications for Stress Identification and Management. In Goldberg L., Brenitz S. Editors: Handbook of Stress. Theorethical and Clinical Aspects: Ed2. New York. (1993): The Free Press
2. Calabrese J., Wilde C. Alterations in Immunocompetence During Stress: a Medical Perspective. In Plotnikoff N. et al. Editors: Stress and Immunity. Boca Raton, Florida. (1991) CRC Press
3. Stoyva J., Budzynski T. Biofeedback Methods in the Treatment of Anxiety and Stress Disorders. In Lehrer P., Woolfolk R. Editors: Principles and Practice of Stress Management. Ed2. New York. (1993): Guilford Press
4. Freeman Lyn. Mosby's Complementary & Alternative Medicine. St Louis, Missouri (2004):14
5. (Source: Roberto Osti/The Scientific American)