How do the connections in the brain work in stress?

In the past few weeks I have made post about the HPA Axis and the Locus Coeruleus systems of the brain. This post will bring it all together for you to understand how they all work together as a team. A true symphony when all working properly.

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The HPA axis and the locus coeruleus systems are linked through the hypothalamus and an area of the brain known as the limbic system. The limbic system is the control area for emotion and the processing area for memory. These linkages are critical. For example, if you see the bushes rustling, your locus coeruleus immediately starts things (the stress response) rolling. However, when you see that it is not a mountain lion but a golden retriever in the bushes, your memory of the tameness of the dog will turn off the stress response. Similarly, if a person is nervous before a public-speaking engagement and the first minute or two goes well, this happy feeling will turn down the activity of the locus coeruleus. These internal adjustments are why experienced public speakers often start off with a joke. It's as much to calm themselves (if the joke goes well) as it is to entertain you.

The connections also include the endogenous (within the body) opiate (opium-like) system and the reward (dopamine) system. Thereby, during stress, pain is reduced and an extremely happy feeling (euphoria) may result. These connections partially account for "runner's high" and have a great deal to do with why we like roller coasters and scary movies.

Here's how the connections work. The limbic system performs an emotional analysis and memory review of the information provided by the senses. Then, the multiplicity of connections allows us to determine whether the current stress is

•one that has been mastered in the past and successfully adapted to,


•not a threat at all, or


•a clear and present danger.


All of this internal activity must occur in milliseconds, and it does.




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What is the role of the hypothalamus-pituitary-adrenal (HPA) axis (grouping) in stress?

The HPA axis is a grouping of responses to stress by the brain and the pituitary and adrenal glands. First, the hypothalamus (a central part of the brain) releases a compound called corticotrophin releasing factor (CRF), which was discovered in 1981. The CRF then travels to the pituitary gland, where it triggers the release of a hormone, adrenocorticotrophic hormone (ACTH). ACTH is released into the bloodstream and causes the cortex of the adrenal gland to release the stress hormones, particularly cortisol, which is a corticosteroid hormone. Cortisol increases the availability of the body's fuel supply (carbohydrate, fat, and glucose), which is needed to respond to stress. However, if cortisol levels remain elevated for too long, then muscle breaks down, there is a decreased inflammatory response, and suppression of the immune (defense) system occurs.

Because they suppress the immune system, corticosteroids in measured doses are used to treat many illnesses that are characterized by inflammation or an overactive immune system, such as asthma and inflammatory bowel disease. For the same reason, they are used to help reduce the chances that our body will immunologically reject a transplanted organ. Corticosteroids also can cause fluid retention and high blood pressure. Therefore, it is critical that the response to corticosteroids be carefully controlled (modulated). This control usually is accomplished by a feedback mechanism in which increased cortisol levels feeding back to the hypothalamus and pituitary turn off production of ACTH. In addition, extremely high levels of cortisol can cause mental changes, including depression and psychosis, which disappear when the levels return to normal.

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