An Analysis of the Biochemical Mechanisms of Stress in the Brain Charlotte Wenk Abstract: Any stimulus, external or internal, that causes a biological response is known as stress, and the compensatory responses to these stresses are known as stress responses. This article will elaborate on what the stress response is, and what occurs neurochemically and hormonally throughout the brain and body during the stress response. Introduction: When a sequence of events consisting of an external or internal stimulus that causes a reaction in the brain, it then activates a physiological fight or flight system in the body.1 This fight or flight system is commonly known as the stress response. Psychological, physiological, and physical, stressors all activate biological stress responses; the biological stress responses involve the release of hormones in the systemic circulation and within central and peripheral tissues. Stress Hormones: The stress response consists mainly of three hormones, norepinephrine and epinephrine, and cortisol. The sympathetic nervous system or SNS releases norepinephrine and epinephrine (as well as adrenaline and noradrenaline) from the adrenal medulla.2 Cortisol is induced by the adrenal gland in the zona fasciculata after the hypothalamicpituitary-adrenal axis or HPA is activated. 1
Dhabhar, Furdaus S., and Bruce S. Mcewen. "Acute Stress Enhances while Chronic Stress Suppresses Cell-Mediated Immunity." Brain, Behavior, and Immunity, vol. 11, no. 4, Dec. 1997, www.sciencedirect.com/science/article/abs/pii/ S08 89159197905080. Accessed 16 May 2020.
Additionally, the HPA axis is responsible for releasing neuropeptides and hormones in the spinal cord, medulla, pons, and higher order centers like the hypothalamus. (See Fig. 1)3 Almost every cell in the body has receptors for cortisol, norepinephrine and epinephrine. These receptors induce changes in cells and tissues throughout the entire body and inform them about the presence of the given stressor.
(Fig 1) Internal Stimuli: Psychological stressors, or stress due to hypothetical events that are not physically occurring, are primarily processed by the limbic system (see Fig. 2), including the hippocampus, amygdala and prefrontal cortex. Both the hippocampus and the amygdala are rich in receptors for cortisol. Amygdala stimulation can provoke the bed nucleus of the stria terminalis to cause the release Corticotropin-Releasing Enhancing Protection and Performance Under Conditions of Threat, Challenge, and Opportunity." NCBI, 26 Mar.2018, www.ncbi.nlm.nih.gov/pmc/articles/PM C596 013/. Accessed 16 May 2020. 3
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2Dhabhar,
Firdaus S. "The Short-Term Stress Response – Mother Nature's Mechanism for
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