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Excerpts:
Stressors are real or perceived challenges to an organism's ability
to meet its real or perceived needs. In most vertebrates the responses that have evolved to cope with such
challenges are constrained by a threshold for detection of challenge, for attention based on real or perceived relevance,
and for capacity to respond at any particular level once the challenge is detected. Depending on the intensity and
timing of the stressor, each of these can vary independently.
Stressors that challenge homeostasis [JLJ - Homeostasis
is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition. Typically
used to refer to a living organism, the concept came from that of milieu interieur that was created by Claude Bernard
and published in 1865. Multiple dynamic equilibria adjustment and regulation mechanisms make homeostasis possible.], often
regarded as the most urgent of needs, are the best known. When an organism's competence to maintain homeostasis within
a specific range is exceeded, responses are evoked that enable the organism to cope by either removing the stressor or facilitating
coexistence with it (Antelman and Caggiula, 1990). While many stressors can evoke dramatic neural and endocrine responses,
a more modest or “subclinical” response may be exhibited in response to milder stimuli. These responses may build
on or extend homeostatic mechanisms or they may be more or less tightly linked to homeostatic responses in a hierarchical
manner creating a functional continuum.
At one level, coping with challenge is what life is all about. Stress is inevitable, and
as Hans Selye emphasized, a necessary part of life (1976).
Stressors may be acute, sequential, episodic, chronically intermittent,
sustained, or anticipated (Sapolsky et al. 2000).
Stress researchers and physiological ethologists often emphasize that stress is evoked by a perceived
challenge to the status quo
There is a great diversity of adaptive behavioral patterns that appear to have built on specific elements
of the stress axes (Table 1).
One of the more striking effects of confronting such a diverse assortment of stress-sensitive phenomena
is vivid sense of the versatility and flexibility of the system. The stress response is orchestrated by a deeply embedded,
highly conservative sense of biological priorities and an impressive economy. By assembling and reassembling a relatively
small number of possible responses into a diversity of new combinations, natural selection deals with an almost infinite array
of possible challenges. Clearly, physiological stress responses need not be manifest as conveniently
conspicuous behavioral patterns or pathologies to have adaptive significance. As David Goldstein (1990) put it, they can
be evoked whenever an organism experiences expectations ---whether genetically programmed, established by
prior learning, or deduced from circumstances—[that] do not match the current or anticipated perceptions of
the internal or external environment (p. 243). In addition, the modulation of stress responses by perceived control
or helplessness (see Cabib and Puglisi_Allegra [1996], and see Seligman [1975], Seligman et al., [1975]) allows us to envision
how an animal’s perception of the prospects for future remediation of a mismatch can influence the expression of an
appropriate compensating response (Bandler et al., 2000).
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