The stress response is activated when the amygdala perceives a threat alerting the hypothalamus of the brain to delegate the stress response. “This region of the brain is responsible for maintaining the balance between stress and relaxation in your body.” (Clark). The hypothalamus will send signals to two main systems involved in the stress response: the sympathetic nervous system (SNS), and the hypothalamic-pituitary-adrenal (HPA) axis. The sympathetic nervous system is responsible for triggering the response directed towards the “fight or flight” reaction. The HPA axis is the body’s energy regulator, and modulates the immune and digestive system in addition to being responsible for regulating many other systems and hormones.
All types of stress, whether psychological, physical or emotional, result in similar activation of the HPA axis. Other regions of the brain feed into the hypothalamus and can either increase or decrease HPA axis activation, including the prefrontal cortex, and the amygdala. The ultimate result of the HPA axis activation is to increase levels of cortisol in the blood during times of stress. The stress response of the HPA axis is closely related to fear expression and fear regulation. The number of traumas a person has experienced also has implications on fear expression. In a study of PTSD patients who had multiple traumas, it was found that the participants did not present an increased fear expression. (Ncbi.nlm.gov) A reduced or dysfunctional HPA axis activation will result in abnormal immune system activation, increased inflammation, allergic reactions, IBS symptoms such as constipation and diarrhea, as well as a reduced tolerance to fatigue, physical, and mental stresses. (MBH.NET).
With any kind of stress: physical, emotional, or spiritual, the body tells the brain “something is not right” and the adrenal glands respond by producing chemical hormones to help the body cope with the stressor. (Caldwell). Even when stress and worry is completely hypothetical and not based on any real or current situation, the amygdala and the thalamus are not able to differentiate this hypothetical stress from the kind that actually needs to be listened to. (Toohill). A state of non-hyper-arousal is needed for the prefrontal cortex to use logical skills for learning and problem solving. (blueknot.org.au).
Once the ‘threat’ is over the body is brought back to a balanced state with a reverse chain of events. The parasympathetic nervous system is responsible for relaxing the body once the stress has been removed from the situation. No ill effects are experienced from the short-term response to stress. (MacDonald).
It is well known that the first depressive episodes often develop after the occurrence of a major negative life event. The diagnosis of a major medical illness often has been considered a severe life stressor and often is accompanied by high rates of depression. For example, a meta-analysis found that 24% of cancer patients are diagnosed with major depression. Stressful life events often comes before anxiety disorders as well. (ncbi.nlm.nih.gov)