How the Stress Response Affects Body and Mind

Change happens quickly in the brain and body when the stress response is triggered and elevated cortisol levels go to work to help you cope with threats and stress.

Flight-fright-freeze are common ways we react when we feel threatened in some way. This stress response stems from the days of survival of the fittest. Individuals who were able to flee or fight off predators or freeze and appear dead when in danger, were the one who lived on to reproduce and raise another generation.

Most of us no longer live with a fear of predators, but a part of the subconscious brain, called the amygdala, remains on the job. It constantly scans the environment for danger. When life-threatening danger is not a daily concern, focusing on and finding problems and perceived threats out of small issues may become its norm.

stress response

Since survival is rarely threatened by a predator these days, the amygdala has taken to alerting us to danger in the face of small conflicts and problems, turning them into big ones. For example, instead of letting insults or other ego threats go by, we respond by getting angry. This gets the stress response rolling. Yes, we all know difficult people with over-zealous amygdalas, including ourselves sometimes!

How the Stress Response Works

When a danger message is sent out, a complex chain of events takes place. It starts in the brain and sets off a multitude of chemical reactions throughout the entire body.

The Locus Coeruleus, a nucleus in the brain stem, sends the stress alert by increasing norepinephrine secretion. Different parts of the brain respond. Dopamine is released, exciting areas of the brain, arousing it and making ready for action. You become more alert and focused. This can be helpful when you need to get things done.

When you feel threatened, the effect is less positive. As more blood flow is sent to the reactive hind brain, instead of the logical reasoning fore brain, you actually become temporarily less intelligent. Your thoughts and behaviors become more automatic and survival oriented. It becomes very difficult to think clearly, make rational decisions and communicate civilly and effectively. 

Much of the stress response is carried out by the Hypothalmic-Pituitary-Adrenal Axis (HPA axis).

The HPA axis is a part of the endocrine system under the control of the nervous system. It controls long-term reactions to stress and regulates body processes including the immune system, sexuality, mood and digestion. The HPA decides when you should store energy and where to send energy if more is needed.

Once norepinephrine is sent to the hypothalamus, it signals the pituitary gland. The pituitary gland signals the adrenal glands to release cortisol and androgens (weak steroids).

The autonomic nervous system responds even faster than the HPA. The ANS is responsible for subconscious functioning of vital organ systems. During the stress response, norepinephrine signals the sympathetic nervous system (SNS) to increase activity. The SNS sends a signal down the spinal cord to the adrenal glands to release adrenaline (epinephrine) in order to speed up metabolism for extra energy.

Because of elevated cortisol and other stress hormones, body and mental functions necessary for fleeing and fighting receive more blood and energy than normal processes. Breathing, heart rate and blood pressure go up. Blood flow to the skeletal muscles increases. Glucose (sugar) is released into the blood stream to fuel  muscles needed to run or fight. This is the classic flight-fright mechanism at work.

Likewise, parasympathetic (PNS) activity decreases.  Functions that are not needed for immediate survival receive less blood and energy than usual. Digestive processes stop or slow. Immune function decreases. If your stress level is high enough, you may even lose control of your bowels and bladder because the energy to control them is needed elsewhere. 

When the threat is past, elevated cortisol levels gradually return to normal. The PNS releases acetylcholine by way of the largest nerve in the body, the vagus nerve, to counter balance the effects of the stress response. Calming, mood boosting serotonin is released.  The digestive system resumes normal function, heart rate slows, you can talk, swallow and breathe easier. Feelings of well being return. Taking a deep relaxing breath stimulates the vagus nerve and tells it to send a calming message to the body.

In the short-term, occasionally triggering the stress response causes no lasting problems to your health. Your brain and body are designed to cope with it as a natural phenomenon. Only when dealing with frequent calls to action does dealing with dis-stress have a significant negative impact on mental and physical health.  

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Source: http://www.health.harvard.edu/staying-healthy/understanding-the-stress-response

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