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Psychobiology of Crisis

A crisis response consists of the reactions that occur following exposure to a critical incident or trauma that may be of either human origin or a natural disaster. The effects of this exposure have been described metaphorically as a “toxin” that enters the body and the mind. One of the best antidotes to attenuate the deleterious effects of this toxin is thought to be the dissemination and receipt of good information. This entry reviews what has been learned about the psychobiological reactions to traumatic events. Knowledge of these reactions may be used to help determine what are adaptive and maladaptive responses to crisis and to educate and treat those experiencing the harmful effects of a crisis.

Overview of the Nervous System

Before describing the purported physiological reactions associated with a crisis, let us briefly review the basic neuroanatomical structures associated with the human stress response. The nervous system is divided into two parts, the central nervous system (CNS), which consists of the brain and the spinal cord, and the peripheral nervous system (PNS), which refers to parts of the nervous system outside the brain and spinal cord (including cranial nerves, spinal nerves, peripheral nerves, and neuromuscular junctions). The human brain has been referred to as being “triune” or having three functional levels: (1) the neocortex, or the highest and most developed part, in which interpretation, gross motor control, logic, memory, problem solving, and planning occur; (2) the limbic system structures (e.g., amygdala, hypothalamus, hippocampus, septum, cingulate gyrus, thalamus), which are located on top of the brainstem and underneath the cortex and are involved in affective or emotional control; and (3) the brain stem and reticular formation, which are involved in vegetative functions. The spinal cord serves as the central pathway for neurons to conduct signals to and from the brain and is involved in autonomically regulated reflexes.

The PNS, which anatomically may be thought of as an extension of the CNS because the functional control centers for the PNS lie in the CNS, is divided into two systems: (1) the somatic nervous system, which carries sensory and motor signals to and from CNS, and (2) the autonomic nervous system (ANS), which innervates the heart, smooth muscles, and glands, and is responsible mostly on an involuntary basis for the regulation of the body's internal environment and the maintenance of homeosta-sis. The ANS is subdivided into two branches: (1) the sympathetic nervous system (SNS), which is concerned with preparing the body for action by generalized arousal of the organs it innervates, and (2) the parasympathetic nervous system, which is concerned with restorative functions and relaxation (often referred to as the “rest and digest” response).

Physiological Reactions Associated with a Crisis

In his seminal work on stress reactions, Walter Cannon wrote extensively on the neuroendocrine process of the ANS role in the stress response and coined the now colloquial concept of the fight-or-flight response. The initial response to exposure to a critical incident or disaster begins primarily with an overwhelming flooding of our senses that then activates the dorsomedial region of the amygdala within the limbic system. Once the amygdalar complex is activated, there is a downward cascade of neural impulses to the lateral and posterior regions of the hypothalamus, which then descend through the thoracic spinal cord, converging at the celiac ganglion (part of the SNS located on the upper part of the abdominal aorta), and then innervating the adrenal gland, or more specifically for the fight-or-flight response, the adrenal medulla (the inner portion of the adrenal gland that sits at the superior poles of the kidneys). The hormones norepinephrine (also referred to as noradrenaline) and epinephrine (also known as adrenalin) are secreted from the adrenal medulla. Norepinephrine is secreted by the adrenal medulla and by adrenergic neurons of the CNS and the SNS. Regardless of the origination of norepinephrine, the effects are the same, including heightened arousal and alertness, elevated heart rate, dilated pupils, increase in blood sugar, and increased stimulation of skeletal muscles.

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