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stress:see strength of materialsstrength of materials,
measurement in engineering of the capacity of metal, wood, concrete, and other materials to withstand stress and strain. Stress is the internal force exerted by one part of an elastic body upon the adjoining part, and strain is the deformation or change in
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Generally, environmental events of a challenging sort as well as the body's response to such events. Of particular interest has been the relationship between stress and the body's adaptation to it on the one hand and the body's susceptibility to disease on the other. Both outcomes involve behavioral and brain changes as well as psychosomatic events, that is, changes in body function arising from the ability of the brain to control such function through neural output as well as hormones. One problem is that both environmental events and bodily responses have been referred to interchangeably as stress. It is preferable to refer to the former as the stressor and the latter as the stress response. The stress response consists of a cascade of neural and hormonal events that have short- and long-lasting consequences for brain and body alike. A more serious issue is how an event is determined to be a stressor. One view is to define a stressor as an environmental event causing a negative outcome, such as a disease. Another approach is to view stressors as virtually any challenge to homeostasis and to regard disease processes as a failure of the normal operation of adapative mechanisms, which are part of the stress response. With either view, it is necessary to include psychological stressors, such as fear, that contain implied threats to homeostasis and that evoke psychosomatic reactions. These are reactions that involve changes in neural and hormonal output caused by psychological stress. Psychosomatic reactions may lead to adaptive responses, or they may exacerbate disease processes. Whether the emphasis is on adaptation or disease, it is essential to understand the processes in the brain that are activated by stressors and that influence functions in the body. See Homeostasis, Psychosomatic disorders
Among the many neurotransmitter systems activated by stress is noradrenaline, produced by neurons with cell bodies in the brainstem that have vast projections up to the forebrain and down the spinal cord. Stressful experiences activate the noradrenergic system and promote release of noradrenaline; severe stress leads to depletion of noradrenaline in brain areas such as the hypothalamus. This release and depletion of noradrenaline stores results in changes at two levels of neuronal function: phosphorylation is triggered by the second-messenger cyclic AMP and occurs in the presynaptic and postsynaptic sites where noradrenaline is released and where it also acts; synthesis of new protein is induced via actions on the genome. Both processes enhance the ability of the brain to form noradrenaline when the organism is once again confronted with a stressful situation. Other neurotransmitter systems may also show similar adaptive changes in response to stressors. See Noradrenergic system
Stress also activates the neurally mediated discharge of adrenaline from the adrenal medulla and of hypothalamic hormones that initiate the neuroendocrine cascade, culminating in glucocorticoid release from the adrenal cortex. Thus, the activity of neurons triggered by stressful experiences, physical trauma, fear, or anger leads to hormone secretion that has effects throughout the body. Virtually every organ of the body is affected by stress hormones. The hypothalamic hormone (corticotrophin-releasing hormone) that triggers the neuroendocrine cascade directly stimulates the pituitary to secrete ACTH. In response to certain stressors, the hypothalamus also secretes vasopressin and oxytocin, which act synergistically with corticotrophin-releasing hormone on the pituitary to potentiate the secretion of ACTH. Various stressors differ in their ability to promote output of vasopressin and oxytocin, but all stressors stimulate release of corticotrophin-releasing hormone. Other hormones involved in the stress response include prolactin and thyroid hormone; the metabolic hormones insulin, epinephrine, and glucagon; and the endogenous opiates endorphin and enkephalin. See Endorphins
Of all the hormones in the endocrine cascade initiated by stress, the glucocorticoids are the most important because of their widespread effects throughout the body and in the brain. The brain contains target cells for adrenal glucocorticoids secreted in stress, and receptors in these cells are proteins that interact with the genome to affect expression of genetic information. Thus, the impact of stress-induced activation of the endocrine cascade that culminates in glucocorticoid release is the feedback of glucocorticoids on target brain cells. The effect is to alter the structure and function of the brain cells over a period of time ranging from hours to days.
In the case of noradrenaline, glucocorticoids have several types of feedback effects that modify how the noradrenergic system responds to stress. Glucocorticoids inhibit noradrenaline release, and they reduce the second-messenger response of brain structures such as the cerebral cortex to noradrenaline. Glucocorticoid feedback also affects the serotonin system, facilitating serotonin formation during stress but at the same time altering the levels of several types of serotonin receptors in different brain regions, which has the net effect of shifting the balance within the serotonergic system. Taken together, evidence points to a role of glucocorticoid secretion in leading to restoration of homeostatic balance by counteracting the acute neural events such as increased activity of noradrenaline and serotonin, which are turned on by stressful experiences. Other neurotransmitter systems may also respond to glucocorticoid action. Moreover, the other hormones activated by stress have effects on the brain and body that must be considered. See Serotonin
In general, stress hormones are protective and adaptive in the immediate aftermath of stress, and the organism is more vulnerable to many conditions without them. However, the same hormones can promote damage and accelerate pathophysiological changes, such as bone mineral loss, obesity, and cognitive impairment, when they are overproduced or not turned off. This wear-and-tear on the body has been called allostatic load. It is based upon the notion that allostasis is the active process of maintaining stability, or homeostasis, through change, and allostatic load is the almost inevitable cost to the body of doing so.
Stress hormone actions have important effects outside the brain on such systems as the immune response. Glucocorticoids and catecholamines from sympathetic nerves and the adrenal medulla participate in the mobilization and enhancement of immune function in the aftermath of acute stress. These effects improve the body's defense against pathogens but can exacerbate autoimmune reactions. When they are secreted chronically, the stress-related hormones are generally immunosuppressive; such effects can be beneficial in the case of an autoimmune disease but may compromise defense against a virus or bacterial infections. At the same time, glucocorticoids are important agents for containing the acute-phase response to an infection or autoimmune disturbance. In the absence of such containment, the organism may die because of the excessive inflammatory response. See Immunology
Besides affecting the immune response, stressors are believed to exacerbate endogenous depressive illness in susceptible individuals. Major depressive illness frequently results in elevated levels of cortisol in the blood. It is not clear whether the elevated cortisol is a cause or strictly a result of the brain changes involved in depressive illness. See Affective disorders
stressa state of tension produced by pressures or conflicting demands with which the person cannot adequately cope. This is therefore subjective in that different people experience the same event differently, and what is experienced as stress by one, may not be by another.
Stress, induced by life events, for example, is relevant in a consideration of psychological disorders (see NEUROSIS), sociological studies of social phenomena (e.g. SUICIDE), and in physical illness (e.g. heart disease). The holistic approach of PERSON-CENTRED COUNSELLING and much of ALTERNATIVE MEDICINE aims to treat the person within the context of the life experience and current problems. To use the mechanical analogy, the aim would be to strengthen the person in order to enable him/her to resist damage from life's pressures.
(1) In engineering, an external force applied to an object and causing deformation.
(2) In psychology, physiology, and medicine, a state of mental tension arising in individuals who function under difficult conditions. The state can arise as a response to either everyday or highly unusual conditions, for example, those attending space flight. The concept of stress was introduced in 1936 by the Canadian physiologist H. Selye in describing the adaptation syndrome. Stress can have both positive and negative effects on behavior and in extreme cases can lead to a total breakdown. The study of human adaptation to complex (extreme) conditions seeks to determine these effects of stress on behavior. Predictions of human behavior, especially behavior under similar conditions, are also concerned with the effects of stress.
REFERENCESLevitov, N. D. O psikhicheskikh sostoianiiakh cheloveka. Moscow, 1964.
Emotsional’nyi stress. Leningrad, 1970. (Translated from English.)
a term used in geology in the narrow sense to designate the one-sided stresses that cause tectonic deformations of rocks and lead to the development of cleavage, schistosity, and dynamic metamorphism. These phenomena in turn give rise to stress minerals (muscovite, chlorite, albite, glaucophane, jadeite, kyanite), which are stable under high pressure. The orientation of the fold axes and of the crystalline forms of the minerals makes it possible to determine the direction of the stress.
(also called accent), the emphasis of certain units of speech through phonetic means. Emphasis is generally placed on syllables, but words and word groups may also be emphasized.
The different types of stress include word stress, breath-group (syntagmatic) stress, and phrasal stress. These types of stress are associated with the linear structure of an utterance that is divisible into segments. A special type of stress—logical stress—is associated with the semantic emphasis of the most important word in a sentence. Stress may be manifested phonetically by increasing the intensity of the stressed syllable. This can be achieved by increasing muscular tension and the intensity of expiration, as in dynamic stress; by varying the voice’s pitch, as in musical accent; or by lengthening the sound, as in quantitative stress.
The most common type of stress is dynamic stress, which exists in many languages, including Russian, English, French, Polish, Hungarian, and Arabic. Musical accent occurs in many languages as well, including Lithuanian, Serbian, the Scandinavian languages, Burmese, Vietnamese, Chinese, and Japanese. Quantitative stress probably does not occur in its pure form, but the feature of length is an important constituent of other types of stress. In Russian, for example, a stressed syllable is emphasized first and foremost by its greater length in relation to the length of unstressed syllables, which may be indistinguishable from stressed syllables in terms of intensity. When a Russian hears long vowels in Czech, in such words as dovésti (“to bring”) or motyl (“butterfly”), he perceives them as stressed vowels, although in actuality stress in Czech always falls on the first syllable. Languages in which length characterizes the vowel phonemes themselves do not use length to achieve stress; in such languages, however, the long vowels in unstressed syllables differ in length from the long vowels in stressed syllables.
Some languages combine all the features by which stress is manifested. In French, for example, a stressed syllable is both more intense and is longer and higher in pitch. Few languages have different types of stress. In Swedish, for example, dynamic stress falls on the first syllable of polysyllabic words, and musical accent falls on one of the succeeding syllables. Danish has, in addition to ordinary dynamic stress, a unique type of stress with a glottal stop (Stød), which, according to many scholars, is a vestige of an earlier musical accent. Dynamic stress may be expressed in the alteration of vowels in unstressed syllables—vowel reduction—which occurs in such languages as Russian and English.
In some languages, for example, Russian, English, and German, primary and secondary stresses may exist within a single word. This often makes it possible to distinguish compound words from combinations of two words with equal primary stresses, as in German Rote Banner (“red banner”) and Rotgardist (“Red Guard”).
Important morphological properties of stress are its mobility and immobility. Mobile stress may be associated with a word’s syllabic structure, as in Polish, or with its morphological structure, as in Russian and English. Russian has mobile stress, that is, some forms of a given word may have stem stress, and others, stressed endings. Mobile-stress paradigms are parallel to declensional and conjugational morphological paradigms and to patterns of word formation.
Stress performs different functions. It can have a distinguishing (significative) function, as in Russian zámok (“castle”) and zamók (“lock”). It can have a demarcative function, as in Czech and Hungarian, which have a special fixed stress that indicates a word boundary, that is, a word’s beginning or end. Stress may also have a unifying (cumulative) function, uniting the elements of a word into a whole.
Stress may alter as languages change over the course of time, and one type of stress may replace another. For example, in most of the Slavic languages, the earlier musical accent, which interacted in a complex manner with acute and circumflex syllabic intonation and with vowel length, became dynamic stress. The law of Fortunatov and de Saussure, in operation during the Balto-Slavic period, regulated stress shifts within word forms and led to the appearance of mobile-stress patterns in morphological paradigms.
REFERENCESMeillet, A. Obshcheslavianskii iazyk. Moscow, 1951. (Translated from French.)
Avanesov, R. I. Fonetika sovremennogo russkogo literaturnogo iazyka. Moscow, 1956.
Zinder, L. R. Obshchaia fonetika. Leningrad, 1960.
Red’kin, V. A. Aktsentologiia sovremennogo russkogo literaturnogo iazyka. Moscow, 1971.
V. A. VINOGRADOV
A system for structural analysis problems in Civil Engineering. STRESS was superseded by STRUDL.
["STRESS: A User's Manual", S.J. Fenves et al, MIT Press 1964].
[Sammet 1969, p. 612].