Neurobiology of the Stress Response
Stress is a normal and essential part of life , enabling body systems to work together to maintain homeostasis and adapt to environmental conditions through the integrated activity of the different parts of the body ’ s stress response system ( SRS ). The components of the stress response system include the central nervous system ( CNS ), the sympathetic adrenal medullary ( SAM ) axis and the hypothalamicpituitary-adrenal ( HPA ) axis . The SAM axis , mediated by epinephrine and norepinephrine , initiates rapid stress responses , while the HPA axis handles longer-term responses through glucocorticoid release . These hormones influence various physiological processes , including metabolism , mitochondrial function , brain activity and the immune system .( 3 )
Physical stressors tend to predominantly engage different parts of the stress response system from those engaged by psychological stressors . Physical stressors are processed by the brainstem and hypothalamus while psychological stressors engage higher brain areas such as the prefrontal cortex ( PFC ), amygdala , and hippocampus .
We have evolved to handle a certain amount of physical and psychological stress . Some would say that our response to stress has not evolved sufficiently from the flight or fight reactions of our ancestors to short term stress to handle what is probably the lower but more chronic levels of stress today . Appropriate levels of physical stressors produced by environmental factors , such as heat , cold , physical load , calorie restriction and hypoxia , can increase tolerance and resilience to psychological stressors through their activation of stress-limiting systems in a process called cross-adaptation .( 4 )
An increase in stress resilience occurs when individuals are able to adapt to psychological and physical stressors . The timing , duration , capacity for recovery and cumulative dose of psychological , physical and biological stressors determine whether a particular stress is beneficial or damaging .
Breathing is both an indicator and a regulator of psychological and body stress . It is one of the few body systems that we can modulate consciously . Different types of breathing practices can be resources for stress management and tools for improving stress resilience .
Good , Tolerable and Toxic Stress
The stress response system , which is essential for adaptation and homeostasis , can cause damage if overactive and persistent , or underactive and unresponsive due to depletion .
Stress can be categorised into tolerable , good and toxic , depending on whether it ’ s within the body ’ s ability to cope and recover and ultimately whether it supports or inhibits homeostasis and adaptation . Understanding the balance between good , tolerable , and toxic stress is crucial for maintaining health and well-being .
Good Stress
Good stress is stress that is within the body ' s capacity to manage , and activates the stress response system just enough to support homeostatic processes . Beyond this , it promotes adaptation to stressors , increasing stress tolerance across various body systems , which ultimately enhances stress resilience . The physiological effects of good stress enable us to use appropriate doses of intermittent stress combined with sufficient recovery to promote healing .
Tolerable Stress
The normal stressors we experience in daily life are tolerable and nondamaging when the stress response system turns off after helping the body achieve homeostasis . When stress is in the tolerable range , stress-activating and stress-limiting processes coexist to create and maintain balance . For example , increased cortisol levels inhibit the stress response once homeostasis is achieved .
Cortisol acts on the hypothalamus , causing it to stop producing corticotropin-releasing hormone ( CRH ). When this inhibitory feedback fails , the stress system malfunctions .
Toxic Stress
While short-term activation of the stress response system within tolerable levels can be beneficial , long-term activation that overwhelms the body ' s capacity to maintain homeostasis can be hazardous and even lethal . Chronic stress activation without normal feedback from stresslimiting systems is observed in many common health conditions like insomnia , obesity , heart disease , depression , anxiety , and in functional syndromes such as fibromyalgia , functional neurological disorders and conditions where symptoms occur in the absence of pathology .
Allostasis and Allostatic Load
Allostasis refers to the stability of physiological parameters in response to changing internal and external conditions ( i . e ., stressors ). The process of allostasis involves the activation of the brain , hormonal , and nervous system components of the stress response system , and helps the body to regain the stable and balanced state of homeostasis necessary for health .
The chemical mediators of allostasis in these systems , such as adrenaline from the adrenal medulla , glucocorticoids from the adrenal cortex , and cytokines from immune cells , act upon receptors in various tissues to produce adaptive changes . However , these changes can be damaging if not properly regulated , leading to receptor desensitization and tissue damage .
Allostatic load is a concept in medicine and psychology that refers to the cumulative burden of stressors on the body ' s physiological systems . It represents the " wear and tear " on the body that accumulates as an individual is exposed to repeated or chronic stress .( 5 , 6 ) Biological , environmental and psychophysiological factors can all contribute to allostatic load . The
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