Pathophysiology of the Human Stress Response Explained

Introduction to the Physiology of Stress

Stress may be defined as the physiological reaction of the human body that acts as a mediation mechanism, connecting a particular stressor with its associated target-organ effect. In this paper, the physiological and anatomical bases of the body's stress response are described within the bounds of historical analysis, theory, and current research outcomes. This is accomplished by (1) tracing psychophysiological effector processes that represent the stress response as defined above, and (2) examining fundamental neuroanatomical structures (Everly & Lating, 2012).

Neurological Foundations and Neural Transmission

A grasp of the stress response requires a discussion of its bases in the function and structure of the nervous system. The nervous system's fundamental functional units are called neurons. Neurons, which conduct motor, regulatory, and sensory signals throughout the body, possess the following basic components: (1) dendrites and postsynaptic dendritic membranes; (2) axon presynaptic membranes — the end points of the telodendria — and telodendria, which are the branching projections of the axon; and (3) the neuron's cell body, which contains the cell's nucleus (Everly & Lating, 2012).

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 body and dendrites. An impulse is then transmitted to presynaptic membranes via the axon and telodendria. From there, the signal is conducted to the next neuron's postsynaptic membrane — a complex task, as neurons are not in actual physical contact with one another (Everly & Lating, 2012).

Neurons are separated by a synaptic cleft, which may be traversed with the help of neurotransmitters. These chemicals reside in storage vesicles in the telodendria and wait for the appropriate cue before moving toward presynaptic membranes. Upon arriving there, they discharge into synaptic clefts to either inhibit or stimulate the succeeding neuron's postsynaptic membrane.

The human body has two basic nervous systems — peripheral and central — which are functional structures housing several million neurons (Everly & Lating, 2012). The central nervous system comprises a "triune" brain with three functional levels, and the spinal cord. The neocortex constitutes the brain's highest and most complex level. In addition to communication, interpreting and decoding sensory signals, and controlling musculoskeletal or motor behavior, the neocortex — 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 because it serves as the brain's affective and emotional control center. This system comprises several neural structures, including the hippocampus, hypothalamus, septum, amygdala, and cingulate gyrus. The pituitary (endocrine) gland plays a key role in the limbic system (Everly & Lating, 2012).

The peripheral nervous system (PNS) comprises all neurons outside the central nervous system (CNS) and consists of two networks: the autonomic and somatic nervous systems. The somatic nervous system transfers motor and sensory signals between the PNS and CNS, innervating both the skeletal and striated musculature and sensory organs. Anatomically, the PNS may be considered an extension of the CNS, as the former's functional control bases reside in the latter (Everly & Lating, 2012).

The human stress response is best understood by analyzing its dynamic process from a systems standpoint — that is, from the perspective of interlinked multidimensionality. A systems model of the human stress response has undergone significant evolution and bears directly upon the phenomenology of the human stress reaction. The model serves as a unifying theme, facilitating better insight into stress phenomenology as well as its treatment and measurement. The model indicates that the epiphenomenology of the human stress reaction consists of complex, interactive processes with numerous major elements:

1. Perceived or actual stressor events.
2. Activation of target organs.
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 as a physiological mediation mechanism (Everly & Lating, 2012).

References

Everly Jr., G. S., & Lating, J. M. (2012). A clinical guide to the treatment of the human stress response. Springer Science & Business Media.

Girdano, D., Dusek, D., & Everly, G. (2009). Controlling stress and tension. Pearson Benjamin Cummings.

Tort, L., & Teles, M. (2011). The endocrine response to stress — a comparative view. In Basic and Clinical Endocrinology Up-to-Date. InTech.