Two amygdalas in brains’ temporal lobes don’t react just to "real" danger like cars in an asphalt jungle as they can also get activated via stress by

• generally rather meaningless sound in low volume, which has earlier been conditioned to pain and
• stimulus that is related to past emotional meaning. Amygdalas react to stress leading effectively to raising of the levels of neurotransmitter glutamine and – via subprocesses – releasing of cortisol hormone to the blood circulation for spreading to organs and tissues of the body.

Cortisol releasing process:

• neurons of hypothalamus make pituitary gland to release adrenocorticotropic hormone
• adrenocorticotropic hormone makes pituitary gland to release corticotropin (ACTH)
• corticotropin travels in the blood circulation and makes cortisol to get released from adrenal glands
• cortisol travels also to many other places in the body like to receptors of the hippocampus and salivary gland (where from it could also be measured)

Normally hippocampus regulates stress response caused by amygdala and keeps release of cortisol in certain limits, but in long-lasting stress ability of hippocampus to control stress weakens.

Stress response controlled by hippocampus gets actually damaged from long-lasting stress and that is because its neurons die. That is because stress hormones (cortisol being just one of them) consume glucose, which is also required as an energy source by hippocampuses’ neurons, and that lead hippocampuses’ neurons becoming vulnerable to excessive amounts of neurotransmitter glutamate (neurotoxicity). Normally neurotransmitter GABA would be used to regulate amounts of glutamate, but even feelings of depression cause GABAergic systems to become less effective.

Stress causes lots of trouble for the operation of hippocampus as among others it disturbs usage of episodical memory, declarative memory and cognitive map. Also, raising cortisol levels affect negatively to front part of the frontal lobe (prefrontal cortex), which has been seen to be related to deduction, emotional control etc.