Sympathomedullary Pathway

6 Key excerpts on "Sympathomedullary Pathway"

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  Coping With Uncertainty

  Behavioral and Developmental Perspectives

  • Davis S. Palermo(Author)
  • 2014(Publication Date)
  • Psychology Press

    (Publisher)

  These physiological processes, evolved to defend the internal environment in the face of external challenge, endow the mammalian organism with a remarkable capability to resist internal disruption despite marked changes in the external environment. This chapter addresses the role played by the sympathoadrenal system in the maintenance of homeostasis. The functional state of the sympathetic nerves and adrenal medulla is directly dependent on regulatory centers within the brain. Input from the cerebral cortex and the limbic system serves to coordinate autonomic activity with cognitive processes and emotional reactions by influencing the activity of the regulatory brainstem centers that initiate sympathoadrenal outflow. These connections play an important physiological role, as described here, in that they prepare an organism to withstand a physiological challenge in anticipation of the acute event. Under certain circumstances, however, recruitment of a sympathoadrenal response may occur in response to perceived threat but in the absence of an appropriate physiological outlet; in situations such as these the resulting physiological changes may be detrimental. These concepts are clarified in this chapter with specific examples. Before proceeding, however, it is necessary to consider the organization of the sympathoadrenal system and methods of assessing sympathoadrenal activity. ORGANIZATION OF THE SYMPATHOADRENAL SYSTEM The sympathetic nervous system and the adrenal medulla form an integrated functional unit referred to as the sympathoadrenal system. Catecholamine release at sympathetic nerve endings and from the adrenal medulla is the direct result of a descending flow of impulse traffic originating in regulatory centers in the hypothalamus, pons, and medulla oblongata. Bulbospinal tracts from these regulatory centers descend in the spinal cord and synapse with typical preganglionic cholinergic neurons in the intermediolateral cell column of the spinal cord

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  Neuroendocrinology of Stress

  • John A. Russell, Michael J. Shipston, John A. Russell, Michael J. Shipston(Authors)
  • 2015(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 5 Stress and Sympathoadrenomedullary Mechanisms

  Regina Nostramo and Esther L. Sabban

  Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York, USA

  Widespread effects of stress on the expression of numerous components of adrenomedullary chromaffin cells. In response to stress, the adrenal medulla receives increased splanchnic nerve input via activation of the sympathoadrenal axis as well as increased exposure to glucocorticoids (CORT) via activation of the hypothalamic–pituitary–adrenocortical (HPA) axis. These and other pathways mediate numerous changes in chromaffin cells (an adrenergic chromaffin cell is pictured: end products of noradrenergic chromaffin cells are indicated in italics). This includes altered expression of catecholamine biosynthetic enzymes, peptides (i.e. enkephalins, neuropeptide Y, urocortin 2, corticotropin-releasing hormone), vesicle-related proteins (i.e. VMAT2, Cgs) and receptors (i.e. AT2 R, B2R). Chromaffin cell–cell communication is also enhanced by increased gap junction formation. Overall, these effects of stress lead to increased catecholaminergic biosynthetic capacity, vesicular storage, chromaffin cell–cell coupling and quantal catecholamine release. ACh, acetylcholine; AT1 R and AT2 R, angiotensin II type 1 and type 2 receptors; B2R, bradykinin B2 receptor; CORT, corticosterone or cortisol; Cgs, chromogranins; DBH, dopamine beta-hydroxylase; Epi, epinephrine; GTPCH, GTP cyclohydrolase; NE, norepinephrine; PACAP, pituitary adenylate cyclase-activating polypeptide; PNMT, phenylethanolamine N-methyltransferase; TH, tyrosine hydroxylase; VMAT2, vesicular monoamine transporter 2.

  5.1 Stress and research on stress

  5.1.1 Definition of stress

  While an individual readily recognizes ‘stress’ when it is experienced, it is not always easy to define. Modern stress theories view stress as a sensed threat to homeostasis

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  The Hypothalamus-Pituitary-Adrenal Axis

  • (Author)
  • 2008(Publication Date)
  • Elsevier Science

    (Publisher)

  Auto-nomic regulations that are represented in the spinal cord, brain, and hypothalamus and are exerted via the peripheral sympathetic pathways are closely integrated with the neuroendo-crine and somato-motor systems. 3. The sympathetic and sympatho-adrenal (SA) systems are involved in the regulation of the immune system, inflammation, and hyperalgesia. In these functions, they are important in the regulation of protection of the body against injury from outside as well as from inside of the body. Details have been described and reviewed in the literature (see Refs [8–23] for groups 1 and 2 and Refs [24–26] for group 3). 2. FUNCTIONAL ORGANIZATION OF SYMPATHETIC PATHWAYS 2.1. Definitions Langley [27] originally proposed the generic term “autonomic nervous system” to describe the innervation of virtually all tissues and organs except striated muscle fibers. Langley’s division of the autonomic nervous system into the sympathetic, parasympathetic, and enteric nervous systems is now universally applied. The definition of the sympathetic and parasympathetic nervous systems is primarily anatomical (the thoracolumbar system or sympathetic system; the craniosacral or parasympathetic system). The enteric nervous system is intrinsic to the wall of the gastrointestinal tract and consists of interconnecting plexuses along its length [28,29]. Organization of the Sympathetic Nervous System 57 In the definition of the terms sympathetic and parasympathetic, afferent neurons are not included. About 85% of the axons in the vagus nerves and up to 50% of those in the splanchnic nerves (greater, lesser, least, lumbar and pelvic) are afferent and are called spinal or vagal visceral afferents. They come from sensory receptors in the internal organs and have their cell bodies in the ganglia of the 9th and 10th cranial nerves and in the dorsal root ganglia of the spinal segments corresponding to the autonomic outflow.

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  Investigating the Psychobiological Stress Response and the Conversion of Cortisol to Cortisone in Human Pregnancy

  • (Author)
  • 2011(Publication Date)
  • Cuvillier Verlag

    (Publisher)

  The main neurotransmitter of the sympathetic postganglionic neurons is norepinephrine (NE), whereas for the PSNS it is ACh. In order to maintain and regain homeostasis, the balance between the activities of the SNS and PSNS are of importance (Iversen et al., 2000). Compared to the HPA axis, the stress response of the ANS is activated within seconds and rapidly terminated again due to the reflex arcs between the SNS and PSNS and the brain stem and spinal cord (Ulrich-Lai & Herman, 2009). The sympathetic stress response in the body’s periphery results amongst others in activation of the sympatho-adrenomedullary (SAM) system. This means that besides the secretion of NE from the postganglionic neurons of the SNS, a secretion of NE (20%), and to a much larger extent epinephrine (EPI; 80%), is induced from distinct neuroendocrine cells within the adrenal medulla called chromaffin cells (Gunnar & Quevedo, 2007; Heim & Meinlschmid, 2003; Ulrich-Lai & Herman, 2009). These chromaffin cells have therefore also been suggested to be regarded as postganglionic neurons (Gunnar & Quevedo, 2007). Subsequently, the released NE and EPI from these chromaffin cells induce various fight-or-flight reactions such as increased heart rate and blood pressure (Iversen et al., 2000). Released EPI, moreover, causes blood glucose to rise, providing the body with sufficient energy (Rizza, Haymond, Cryer, & Gerich, 1979). The parasympathetic reaction to stress in the periphery leads to a withdrawal of ‘vagal tone’ and to a greater activation of the sympathetic nervous system (Ulrich-Lai & Herman, 2009). Feedback is 4 Autonomic ganglia are accumulations of nerve cell bodies (Breedlove et al., 2010). 16 dynamically regulated, since the vagus nerve is comprised of both afferent (i.e. carrying information to the brain, also known as sensory nerve fibres) as well as efferent nerve fibres (i.e. carrying information away from the brain, also known as motor or effector nerve fibres; Porges, 1995).

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  Stress and Addiction

  Biological and Psychological Mechanisms

  • Mustafa al'Absi(Author)
  • 2011(Publication Date)
  • Academic Press

    (Publisher)

  In general, the adre-nal medulla may function in concert with the sympathetic nervous system, or it may function somewhat independently in meet-ing homeostatic demands (Kvetnansky and McCarty, 2000). Besides extreme heat or cold, pain, blood loss, and lack of oxygen supply, etc., physical effort (e.g., physical labor, exer-cising like bicycle ergometry and treadmill running) and psychological stress (e.g., parachute jumps, exams, free speeches, cognitive conflict tasks, the Trier Social Stress Test) activate catecholamine release (Axelrod and Reisine, 1984; Mason, 1968b; Schommer et al., 2003). Interestingly, under repeated psychosocial stress, the reactiv-ity of the HPA axis and the SAM system dissociates. Although HPA axis responses quickly habituate, the SAM system shows rather uniform activation patterns with repeated exposure to psychosocial chal-lenge (Schommer et al., 2003). The funda-mental role of catecholamine secretion is the rapid mobilization of stored energy depots (e.g., supply of free fatty acids and glucose, glucogenolysis, lipolysis) and to downregulate less important organ func-tions (e.g., the gastrointestinal tract, repro-duction; see also below). In respect to cardiovascular functioning during stress, catecholamines mediate the so-called defense reaction with increases in heart rate, cardiac output, and blood pressure (for reviews, see Hjemdahl, 2000; Pollard, 2000). Catecholamines also facilitate the oxygen supply via dilatation of the bron-chial tubes; enhance platelet aggregation and reduce clotting time (see below); and impact on the vascular smooth muscles causing the shunting of blood away from the skin, mucosa, and kidney to the coro-nary arteries, skeletal muscle, and the brain. Furthermore, central noradrenergic neurons terminate in the PVN and synapse on CRH neurons directly activating CRH neurons (see above).

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  Principles Of Biopsychology

  • Simon Greene(Author)
  • 2013(Publication Date)
  • Psychology Press

    (Publisher)

  As I pointed out at the beginning of this chapter, psychology has found emotion an elusive topic to study. Even today there is no agreed definition of the term, and at least 30 current models. Research on the central and peripheral biological mechanisms has clarified some issues, and led to systematic and inventive experiments. We can make some general statements, but detailed psychobiological models will have to wait until we have a psychological analysis of emotional experience and behaviour that we can all accept.

  Summary: Stress, Anxiety, and Emotion

  • Stress exists when there is a mismatch between perceived demands and perceived coping ability. It can be energising, but long-term chronic stress can also lead to psychological and physiological problems.
  • The adrenal gland plays a central role in the physiological responses to stressors. The adrenal cortex releases corticosteroids in response to the hormone ACTH which is secreted from the pituitary gland. As the pituitary is in turn controlled by the hypothalamus, this chain is known as the hypothalamic-pituitary--adrenal axis.
  • In stressful situations the autonomic nervous system (ANS) activates the adrenal medulla, which releases adrenaline and noradrenaline into the bloodstream. General ANS activation and the release of hormones from the adrenal gland produces a pattern of peripheral arousal in the body. If the stressor is short-lasting, the arousal fades away; its basic purpose is to supply the energy needs involved in behavioural coping responses.
  • Selye identified the General Adaptation Syndrome. Physiological stress responses go through stages of alarm, resistance, and exhaustion when confronted by chronic stressful situations.
  • Coping responses to modern day stressors do not always involve physical activity, and the physiological arousal found in these situations therefore becomes maladaptive and can lead to psychosomatic disorders.
  • The work of Brady and Weiss with animals has shown that physical reactions to stressors are influenced by individual differences and by feedback on successful coping behaviour.
  • Frankenhaeuser demonstrated that adrenaline release is sensitive to any arousing stimulation. Males show a more vigorous adrenaline release than females in stressful situations, although this may not apply to females in non-sex role stereotyped roles.

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