von Tanja Martens-Mantai
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| [1.] Tmm/Fragment 002 01 - Diskussion Zuletzt bearbeitet: 2014-04-25 09:06:46 Singulus | Fragment, Gesichtet, Granz 2009, SMWFragment, Schutzlevel sysop, Tmm, Verschleierung |
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| Untersuchte Arbeit: Seite: 2, Zeilen: 1-15, 18-28 |
Quelle: Granz 2009 Seite(n): 6, 7, Zeilen: 6: 1ff; 7: 1ff |
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| Introduction
Spreading depression (SD) is a pathophysiological phenomenon which exhibits as a propagating wave of neuronal and glial hyperexcitability of few seconds followed by a transient wave of depression of few minutes and later subsides with another longduration hyperexcitability, first identified in the cerebral cortex of rabbits (Leao, 1944; Somjen, 2001; Gorji, 2001). The SD phenomenon is exclusive to the central nervous system and influences both the neuronal and the glial cells in different parts of the central nervous system including both brain and spinal cord. SD propagated in all neuronal tissues in both vertical and horizontal directions. SD probably starts with a cellular efflux of K+, leading to depolarization and a period of relative electrical silence. The subsequent energy-dependent restitution of ion gradients eventually restores normal neuronal activities. The ionic activity, however, results in a wave of neuronal depolarization propagating away from the elicitation site at a velocity of 2-5 mm/min. Because the depolarization-restoration process takes 1.5 min, the wave is only ~5mm deep (Smith et al., 2006). [...] SD involves a temporary localized redistribution of different ions between intracellular and extracellular spaces. This ion redistribution is energy dependent. During eliciting of SD the concentration of extracellular K+ ([K+]o), rapidly rises (up to 60mM), causing brief neuronal excitation then depolarization and a period of electrical silence during which DC potential at the brain surface falls. In tandem, extracellular sodium ([Na+]o) and chloride ([Cl−]o) levels decrease as these ions enter cells. Consequently, water enters cells, the extracellular space is reduced, and cells swell. Ca2+ ions also move inwards, but slightly later than the outward movement of K+, suggesting that Ca2+ movements follow K+ fluxes. Additional negative ion species move outwards to maintain electrical balance, the excitatory neurotransmitter glutamate probably being the most crucial (Nicholson and Sykova, 1998; Somjen et al., 2001). |
I. Introduction
Spreading depression (SD), is a physiological/pathophysiological phenomenon which manifests as a propagating wave of neuronal hyperexcitability followed by a transient wake of depression, first identified in the cerebral cortex of rabbits (Leao, 1944; Gorji, 2001). The SD phenomenon is exclusive to the central nervous system and appears to influence both the neuronal and the glial cells. [page 7] SD probably starts with a cellular efflux of K+, leading to depolarization and a period of relative electrical silence. The subsequent energy-dependent restitution of ion gradients eventually restores normal neuronal activities. The ionic activity, however, results in a wave of neuronal depolarization propagating away from the elicitation site at a velocity of 3 mm/min. Because the depolarization-restoration process takes 1.5 min, the wave is only ~5 mm deep (James et al., 2001). SD involves a temporary localized redistribution of different ions between intracellular and extracellular spaces. This ion redistribution is energy dependent. During eliciting of SD the concentration of extracellular K+ [K+]o, rapidly rises (up to 60mM), causing brief neuronal excitation then depolarization and a period of electrical silence during which DC potential at the brain surface falls. In tandem, [Na+]o and [Cl−]o levels decrease as these ions enter cells. Consequently, water enters cells, the extracellular space is reduced, and cells swell. Ca2+ ions also move inwards, but slightly later than the outward movement of K+, suggesting that Ca2+ movements follow K+ fluxes. Additional negative ion species move outwards to maintain electrical balance, the excitatory neurotransmitter glutamate probably being the most important (Somjen et al., 2001). |
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