When it comes to the response of humans, the brain takes all the credit. This organ responds to stress, among others things since it is the specific organ that determines a threat that may be stressful or not. It also controls the behavioral and psychological responses that may either be damaging or adaptive. Doing this the brain relies on many structures which are crucial to its functioning; these structures are the amygdala, hippocampus, and prefrontal cortex. Under stressful situations, these structures may undergo structural remodeling, and the resultant effect is that the psychological and behavioral responses may be altered ( The Rockefeller University, 2017) . The amygdala is a very significant structure located within the uncus in the anterior temporal lobe. This structure is responsible for the reciprocal connections within the brain in hypothalamus, hippocampus, brain stem, and orbital frontal cortex among others. This structure is the center for the coordination of behaviors, endocrine, and the automatic responses. Amygdala responses focus on some stimuli, especially emotions, though it specifically targets those that are anxiety or fear related. Another structure is the Hippocampus which is a cerebral cortex with three layers located within the temporal lobe in the medial aspect. This structure helps in controlling the production of corticosteroid. Another thing is that it is actively involved in a number of declarative functions among others. The prefrontal cortex, on the other hand, is the premotor cortex's anterior. In humans, this part is well developed thus having a critical impact when it comes to motivation, judgment, mood, insight and emotional reactions. Its function is on mood disorders, especially abnormal moods. All these structures interact thus influencing each other through indirect and direct neural activity. For instance, an inactivate amygdala inhibits stress-related impairment to the hippocampal long-term potentiation (LTP) and spatial memory. It also affects basolateral amygdala stimulation enhances danteterus field potentials and at the same time stimulate medial prefrontal cortex which decreases central amygdala’s output neurons responsiveness. The processing of emotional memories accompanied by contextual information depends on amygdala-hippocampal interactions, while the prefrontal cortex, through its powerful influence on the amygdala, serves a crucial role in killing four.
There is a kind of stress response referred to as the glucocorticoids, which is capable of damaging the brain. The process of responding to stress involves the activation of the amygdala, which, as a result, transmits signals, thus alerting the organism of a pending threat. As a result, hypothalamic-pituitary-adrenal (HPA) is activated which leads to the axis and generation of torrents of hormones (Greenberg, 2012). One of the hormones released is cortisol, which is mostly referred to as the stress hormone (quintessential), the resultant effect affects the brain depending on the duration of the stress hormone being active. The short-term release of cortisol prepares one to sustain “fight or flight” and counter an attacker. On the other hand, long-term exposure to cortisol causes the brain neurons to shrink and restricts their capacity to send and receive impulses via branches known as dendrites (Greenberg, 2012). In the study of animals, under certain conditions where the stress is chronic, glucocorticoid (cortisol) is capable of maintaining its elevated levels for longer periods (Greenberg, 2012). More so, chronic stress can result to the shrinking of the neurons that are present in the medial prefrontal cortex; reducing the density of the spine and dendrites simplification.
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Hippocampal cells have been affected by stress hormones, thus affecting its functioning among other things. Most effects of stress on the hippocampus result from uncontrollable stress; usually, it is affected at many levels. Considering the studies on animals and human behaviors, it has been found that memory tasks dependent on the hippocampal structure are the primary target of stress. Animal studies show that stress alters the ensuing synaptic firing properties and plasticity of the hippocampal neurons. Also, both studies (animal and human) have suggested that stress can also alter the morphology of a neuron, reduce the hippocampal volume, and suppress the proliferation of the neuron thus tempering its (hippocampus) structure (Kim, Pellman, & Kim, 2015). Hippocampus is not the only brain structure that is affected by stress hormones, but also other structures like the amygdala. This is the structure that receives information first from the ears and eyes thus interpreting it. In animal studies, it was found that when the amygdala is under chronic stress, it grows and becomes large. At the same time, the stress caused the hippocampus dendrites to shrink (McEwen, Nasca, & Gray, 2016).
The result of stress on amygdala and hippocampus structures may be so severe to the individual causing several implications. Researchers have it that the effects of the shrinking of the hippocampus dendrites and the growth of amygdala altogether are capable of resulting in elevated levels of fear and anxiety (McEwen, Nasca, & Gray, 2016). As the amygdala continues to grow, more fear and anxiety is experienced. “The amygdala usually becomes bigger with increased activity in depressed people. But because the hippocampus cells that support memory are shrinking and thus unable to transmit impulses effectively, affected individuals find it increasingly difficult to connect their feeling of fear with their memory of actual events that took place. The individuals develop generalized anxiety (McEwen, Nasca, & Gray, 2016).
There is another process that takes place within the human brain, neurogenesis. Neurogenesis is the process whereby neurons, which are functional are generated from neural precursors, which occur throughout the lifetime of mammals. It includes the division, differentiation, and migration of cells. The process of neurogenesis occurs within the two parts of the brain that is, the hippocampus’ dentate gyrus and the lateral ventricles’ subventricular zone (McEwen, Nasca, & Gray, 2016). Hippocampus is not only responsible for memories, but it is also the center for the regeneration of the brain. It continuously produces cells that are progenitors which are capable of differentiating into glia and neurons which migrate to regions of the brain in need of replenishment. More so, neurogenesis ensures that enough cells are generated to ensure that the brain remains active in its role, especially the hippocampus, which is very significant to every mammal.
Instances of traumatic stress are usually associated with elevated levels of norepinephrine and cortisol responses to the subsequent stressors. Antidepressants are usually used to counteract and eliminate stress on the hippocampus. Traumatic memories have severe effects on the brain simply because it is associated with the potentiated cortisol release in (post-traumatic stress disorder) PTSD (McEwen, Nasca, & Gray, 2016). PTSD is usually characterized by precise symptoms such as hyperarousal, sleep disturbances, and nightmares, flashbacks, and intrusive thoughts among others (McEwen, Nasca, & Gray, 2016). These characteristics are capable of causing increased levels of depression in a person.
The brain is a very crucial part of the human body. It requires critical approaches which can ensure that the negative effects of chronic stress are counteracted and prevent the brain from shrinking. Every individual can prevent the brain from shrinking; the ways of doing so include brain-centered interventions, which are familiar to the daily lives of humans. These include improving the quality and quantity of sleep, changing to a positive from negative life outlook, and eating healthy among others. Another thing is engaging in physical activity which is very beneficial to the metabolic and cardiovascular and brain systems. Voluntary engagement in physical activity results in an increase in neurotrophin presence within the cortex and hippocampal sections of the brain (The Rockefeller University, 2017). Also, taking daily supplements of DHA, which contains fatty acids of Omega-3; is crucial for the building of brain cells (Greenberg, 2012). DHA combats the cortisol inflammatory effects as well as the plaque buildup related to susceptibility to Alzheimer’s disease.
References
Greenberg, M. (2012, Aug. 12). How to Prevent Stress from Shrinking Your Brain. Psychology Today . Retrieved from psychologytoday.com/blog/the-mindful-self-express/201208/how-prevent-stress-shrinking-your-brain.
Kim, E. J., Pellman, B., & Kim, J. J. (2015). Stress effects on the hippocampus: a critical review. Learning & Memory , 22 (9), 411–416. http://doi.org/10.1101/lm.037291.114
McEwen, B. S., Nasca, C., & Gray, J. D. (2016). Stress Effects on Neuronal Structure: Hippocampus, Amygdala, and Prefrontal Cortex. Neuropsychopharmacology , 41 (1), 3–23. http://doi.org/10.1038/npp.2015.171
The Rockefeller University. (2017). Stress Effects on Structure and Function of Hippocampus . Retrieved from http://lab.rockefeller.edu/mcewen/stresshippo
