Pathophysiology of Stress Reaction Stress may be defined as the physiological reaction of the human body which acts as the mediation mechanism, connecting a particular stressor with its associated target- organ effect. In this paper, the physiological and anatomical bases of our body’s stress response will be described, within the bounds of historical bases and analyses, theories and latest research outcomes, through (1) tracing psychophysiological effector processes actually representing the above- defined stress response, and (2) dealing with fundamental neuroanatomical structures (Everly & Lating, 2012).

Neurological Foundations

A grasp of the concept of stress response necessitates a discussion of its bases, residing in the nervous system’s function and structure. The nervous system’s fundamental functional units are called neurons (see Fig.1).

Neurons, which conduct motor, regulatory and sensory signals all through the body, possess the following basic units: (1) dendrites and postsynaptic dendritic membranes; (2) axon presynaptic membranes (end points of the telodendria) and telodendria (the axon’s branching projections); and (3) the neuron’s cell body that contains the cell’s nucleus (Everly & Lating, 2012).

Fig 1. A typical neuron

Neural transmission

Incoming signals first reach postsynaptic dendritic membranes. When these membranes are stimulated, ionotropic (electrical) and metabotropic (chemical) processes commence, with the neuron conducting incoming signals via the cell’s body and the dendrites. Lastly, an impulse is transmitted to presynaptic membranes via the axon and telodendria. From here, the signal is conducted to the next neuron’s postsynaptic membrane, which is a complex task as neurons aren’t in actual physical contact with each other (Everly & Lating, 2012).

Neurons are separated by a synaptic cleft, which may be traversed through the help of neurotransmitters. These chemicals that reside in the telodendria’s storage vesicles wait for the right cue before moving towards presynaptic membranes. After reaching there, they eventually discharge into synaptic clefts for inhibiting or stimulating the succeeding neuron’s postsynaptic membrane.

The subsequent step in this study will be to analyze human stress reaction’s basic anatomical structures. The human body has two basic nervous systems, peripheral and central, which are functional structures that house several million neurons (see fig 2) (Everly & Lating, 2012).

Fig 2. Nervous systems

The central nervous system comprises of a ‘triune’ brain (with 3 functional levels) and spinal cord. The neo- cortex constitutes the brain’s highest and most complex level. Besides communication, interpreting and decoding sensory signals, and controlling overall musculoskeletal or motor behavior, the neo- cortex (especially its frontal lobe) controls imagination, memory, logic, planning, apprehension, decision making, and problem solving (Everly & Lating, 2012).

The next functional level’s key element is the limbic brain, whose discussion is vital to the subject of stress, owing to its being the brain’s affective/ emotional control center. This system comprises several neural structures, including the hippocampus, hypothalamus, septum, amygdala, and cingulate gyrus. The pituitary (endocrine) gland has a key role in the limbic system (Everly & Lating, 2012).

The peripheral nervous system (PNS) comprises all neurons excluding the central nervous system (CNS) and has two networks), namely autonomic and somatic nervous systems. The latter transfers motor and sensory signals between the PNS and CNS, innervating both the skeletal/ striate musculature and sensory organs. The PNS can, anatomically, be considered a CNS extension as the former’s functional control bases reside in the latter (Everly & Lating, 2012).

Human stress reaction may be best understood by analyzing its dynamic “process”, which can be defined from a “system” standpoint, i.e., from the perspective of interlinked multidimensionality. Fig. 3 depicts the systems perspective that has undergone significant evolution of late and which bears upon the human stress reaction phenomenology. The model serves as the uniting theme,...

Fig.3 indicates that human stress reaction’s epiphenomenology is that of complex interactive processes that possess numerous major elements:
1. Perceived or actual stressor events.

2. Activation of target organ.

3. Affective integration and cognitive evaluation.

4. Coping behavior

5. Neurological stimulating mechanisms (for instance, locus ceruleus, hypothalamic nuclei and limbic nuclei).

6. Stress reaction (a physiological mediation mechanism) (Everly & Lating, 2012).

Fig. 3 A systems model of the human stress response

Stressor Events

Stressor events may be categorized into: (1) biogenic and (2) psychosocial stressors (Girdano, Dusek, & Everly, 2009). The latter represent perceived or actual environmental events which set the scene for stress reaction production. They aren’t able to cause stress reactions directly; rather, they need cognitive evaluation mechanics. In fact, a majority of stressors are psychosocial stressors. On the other hand, biogenic stressors are the actual causative elements of stress reaction production. These stimuli get around higher cognitive evaluation processes, working directly on the neurological and affective stimulating nuclei. Therefore, owing to their biochemical facets, they trigger stress reaction directly without the customary required affective-cognitive processing (Everly & Lating, 2012). Biogenic stimuli include:

· Nicotine

· Ginseng

· Caffeine and

· Extreme cold or heat, pain- causing stimuli and other such physical factors

Cognitive–Affective Domain

Realistically, “reality” doesn’t exist if one fails to consider the human perception which potentially bears upon it. This model outlines the affective- cognitive domain for capturing this concept. Cognitive evaluation denotes the cognitive interpretation process (or, in other words, the meanings assigned to the universe unfolding before us). Further, affective integration denotes the coloring and mixing of experienced emotions into cognitive interpretation, which leads to an affective- cognitive complex which reflects the way stressors are eventually felt. Basically, this crucial integrated view implies an ascertainment of whether or not the psychosocial stimuli get converted into stressors. But this perceptual process is personalized uniquely, and susceptible to personality trends, biological dispositions, available coping resources and learning history. While Fig.3 depicts a mutuality between affective and cognitive mechanisms, one point to bear in mind is: considerable evidence exists in support of the cognitive primacy theory, which claims that cognition governs perceived emotion or affect, thereby assuming a superordinate part when restructuring human behavioral trends (Everly & Lating, 2012).

As previously observed, appraisal represents a function of all extant coping resources on hand, biological dispositions, personality trends, and learning history. After evaluation is carried out, efferent impulse projects to the following, for potentiating stimulation of key effector systems:

1. The limbic system’s extremely sensitive affective anatomy, particularly the hippocampus region, for experiencing stimulus- specific sensed emotion, in addition to the ability of triggering visceral effector processes.

2. Neo- cortex regions related to neuromuscular behavior; here, tension or muscle tone increased via extrapyramidal and pyramidal systems, with the intent to act being translated, potentially, to real evident motor activity (Everly & Lating, 2012).

Up until now, one may have understood that after being perceived, psychosocial stimuli stimulate general arousal and cognitive evaluation mechanisms. Stimuli that are evaluated as being of a threatening, challenging or abhorrent nature will probably lead to emotional arousal. In a majority of persons, limbic center activation for emotional stimulation results in the expression of sensed emotions as neuromuscular and visceral activity. This neuromuscular and visceral activation denotes the multi- axial physiological mediation mechanisms known as “stress response”.…