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are some of the physiological indexes used to assess stress. A disadvantage of these procedures is that the equipment and the setting may themselves produce stress. 2. Life Events Scales Most life events scales are patterned after the Holmes and Rahe Social Readjustment Rating Scale, an instrument that emphasizes change Defining and Measuring Stress Chapter 5 The Nervous System and the Physiology of Stress • The nervous system is made-up of neurons (nerve cells) that provide internal communication by releasing chemical neurotransmitters across the synaptic cleft (the space between neurons). The billions of connections among neurons provide for complex actions. The nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord and all the other nerves in the body are in the peripheral division (see Figure 5.1). • The Peripheral Nervous System • The peripheral nervous system is also divided into two divisions, the somatic nervous system, which consists of the nerves that activate voluntary muscles in the body. The autonomic nervous system (ANS) serves internal organs and glands and works automatically. Although conscious control of autonomically controlled reactions is possible, this control requires training. • The ANS is also divided into two parts, the sympathetic and parasympathetic divisions (see Figure 5.2). These two divisions act reciprocally, the sympathetic increasing its activity in emergency or stress situations and the parasympathetic acting in normal situations. • Neurotransmission in the ANS is conducted mainly by two chemicals, acetylcholine and norepinephrine, which exert complex effects. • The Neuroendocrine System • • The endocrine system consists of ductless glands, and the neuroendocrine system consists of endocrine glands controlled by the nervous system. These glands release hormones that travel through the blood and act on target organs (see Figure 5.3). 1. The Pituitary Gland • The pituitary gland is located in the brain and releases a number of hormones that affect target organs in many parts of the body. One pituitary hormone—adrenocorticotropic hormone (ACTH)—acts on the adrenal glands. • 2. The Adrenal Glands • • The adrenal glands are located on top of the kidneys and contain two structures that produce different hormones, the adrenal cortex (outer covering) and the adrenal medulla (inner structure). The adrenocortical response occurs when ACTH stimulates the adrenal cortex to secrete glucocorticoids, the most important of which is cortisol. The adrenomedullary response is activated by the sympathetic nervous system and secretes catecholamines, including epinephrine and norepinephrine. • The Physiology of the Stress Reaction • The stress reaction mobilizes body resources in emergency situations. One route occurs through activation of the sympathetic nervous system, which is called the adrenomedullary response. The other route is through the hypothalamicpituitary-adrenal axis and involves all these structures. The response of the hypothalamus prompts the pituitary to stimulate the adrenal cortex to produce glucocorticoids, including cortisol. (See Figure 5.4 for these two routes of activation.) • Maintaining an appropriate level of activation calls for varied levels of activation of the peripheral nervous system. This process is called allostasis, but prolonged activation of the sympathetic nervous system creates allostatic load, which may cause problems. • Shelly Taylor and her colleagues have proposed that this “fight or flight” model may be more appropriate for men; women may manage stress through a “tend and befriend” strategy. Theories of Stress • Hans Selye and Richard Lazarus proposed influential theories of stress. A. Selye's View • • • Selye's theory defined stress as a nonspecific or generalized response to a variety of environmental stressors. Whenever the body encounters a disruptive stimulus, it mobilizes itself in a generalized attempt to adapt to that stimulus. 1. The General Adaptation Syndrome • • • This mobilization is called the General Adaptation Syndrome (GAS). The GAS has three stages—alarm, resistance, and exhaustion. The potential for trauma or illness exists at all three stages (see Figure 5.5). 2. Evaluation of Selye’s View • • • Selye concentrated on the physiological aspects of stress, downplaying the psychological ones, and ignoring the perceptual and interpretative processes that can moderate the human experience of stress.