Das Verhalten der B-Fasern des Froschvagus bei Ersatz des Natriums der Au�enl�sung durch quatern�re Ammoniumionen

H, Bockendahl; Meves, H.

doi:10.1007/bf00362365

Cited by 3 publications

(2 citation statements)

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“…Ba++ cannot substitute for Na+ in frog A fibers (42) , The conclusion that such and other cations serve as diffusing charge has been most strongly supported by their ability, at increasing concentrations, to contribute in creasingly to the rate of depolarization or to the amplitude of the spike during excitation. This conclusion remains to be validated by analytical data such as were obtained earlier for sodium, for other interpretations of the results are possible (9,55,101). In any case, whether these interpretations are vali d or not they serve to focus attention on the change in the excitable membrane which causes cations to be transferred more readily during excitation rather than on the specific ion involved.…”

Section: Spikementioning

confidence: 69%

“…The de pendence of the rate of spike development and of spike amplitude on extra cellular sodium concentration, (Na)o, and more recently (6) on intracellular concentration, (Na)i (since the maximum reversal of potential during the peak of the spike is given by 59 10g[(Na) i/(Na) o] in millivolts at 25°C when PNa greatly exceeds other permeabilities) , to be expected from this view, has been verified in additional fibers, such as cockroach, lobster, and crayfish giant axons (16,17,119) and B fibers of the frog vagus (9) . In such studies a suit able substitute for Na+ must be used that will not function like Na+.…”

Section: Spikementioning

confidence: 83%

See 1 more Smart Citation

Drugs and Nerve Conduction

Shanes¹

1963

Annu. Rev. Pharmacol.

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Propagation of the action potential in nerve fibers is dependent on two related processes-the electrical excitability of the membrane ahead of the actively depolarized region, and the magnitude and temporal characteristics of the transitory depolarization that constitutes the action potential. The now classical work of Hodgkin (45, 46) on vertebrate nerve trunks demon strated the dependence of conduction on the electronic spread of depolariza tion induced by "local current" from the region of the action potential to that ahead of it to cause enhanced excitability and excitation. The subsequent studies of Tasaki and associates, and others on large, single myelinated fibers, summarized in Tasaki's monograph (97), were of special importance in demonstrating saltatory conduction (i.e., conduction by activation of successive nodes of Ranvier) and a safety factor of 5 to 7 (i. e. , that the action potential is 5 to 7 times larger in maximum amplitude than that just needed to excite the adjacent node of Ranvier); moreover, Tasaki & Takeuchi (103) showed that the threshold of excitability and the height of the action poten tial vary inversely, as might be expected from recent evidence that both are normally dependent on the ability of the excitable membrane to undergo permeability changes to Na+ and K+ (84,87,104). The process of conduction is dependent not only on the kinetics of the transitory permeability changes underlying excitability and the action potential, but also on the physical conditions governing the spread of local current ahead of the action potential. Among the physical conditions are (a) the critical length of the fiber, determined by the resistances of the mem brane, axoplasm, and extracellular spaces, which governs the spatial features of the electrotonic spread of depolarization ahead of the action potential, and (b) the capacitance of the excitable membrane and other structures (myelin) that, with the associated resistance, determines the temporal characteristics of the rise of the electrotonic potential. These have been reviewed recently by Fatt (30). Of course, the presence of heavily myelinated internodes that give rise to saltatory conduction in "myelinated" nerve, as distinguished from continuous propagation in "unmyelinated" (actually weakly myelinated) fibers, is also an important consideration in any general analysis of conduction among different fibers. Since the resistances, capaci tances, and general histology vary with fiber size, everything else being equal 1 The survey of the literature pertaining to this review was concluded in July 1962. , Preparation of this article was supported by research grants from the National Institutes of Health, B-3321 and B-3322. 185 Annu. Rev. Pharmacol. 1963.3:185-204. Downloaded from www.annualreviews.org Access provided by University of Wisconsin -Madison on 06/21/16. For personal use only. Quick links to online content Further ANNUAL REVIEWS

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Section: Spikementioning

confidence: 69%