Die Signalübermittlung im Nerven

Muralt, Alexander v.

doi:10.1007/978-3-0348-4163-4

Cited by 45 publications

(6 citation statements)

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“…The constrictions extend for so short a distance along the fibre, however, that it is justifiable to neglect their effect on resistance. Our analysis might, however, be seriously affected if the axis cylinder is interrupted by transverse membranes across which potential differences can be developed, as suggested by von Muralt (1945). It is difficult to say how this theory would alter our analysis, since it has not yet been given quantitative expression.…”

Section: Discussionmentioning

confidence: 97%

Evidence for saltatory conduction in peripheral myelinated nerve fibres

Huxley¹,

Stämpfli²

1949

The Journal of Physiology

581

236

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Section: Discussionmentioning

confidence: 97%

Evidence for saltatory conduction in peripheral myelinated nerve fibres

Huxley¹,

Stämpfli²

1949

The Journal of Physiology

581

236

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“…The processes serving the quick transmission of nerve impulses cannot therefore be responsible for the maintenance of 102 continuity of a nerve fibre. Muralt (1945) distinguishes between external and internal signals in nerve fibres, the latter serving the maintenance of reactivity (Betriebsbereitschaft und Betriebssicherheit). This term is a very vague one and unless explained more accurately seems to serve no more purpose than the equally vague term " trophic influence ".…”

Section: Discussionmentioning

confidence: 99%

“…The time at which this failure of transmission of nerve impulses can be recorded is apparently not a constant value. It is for instance known that both the metabolic rate and temperature influence the rate of degeneration (Muralt, 1945). Additional information about the factors affecting the rate of degeneration should help in understanding the mechanism of "Wallerian degeneration".…”

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confidence: 99%

“…A much more complicated problem is the evaluation of the criteria of degeneration in the morphological sense. Muralt (1945) states that morphological changes generally appear only a long time after loss of excitability of the nerve fibres. The first changes in the axons, however, are observed much earlier (Ram6n y Cajal, 1928) and changes in the myelin sheaths studied by the polarized light method are observed, within 24 hours of nerve section (Prickett and Stevens, 1939).…”

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confidence: 99%

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The Degeneration of Peripheral Nerve Fibres

Gutmann¹,

Holubar²

1950

Journal of Neurology, Neurosurgery & Psychiatry

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After section of a peripheral nerve a series of processes occurs in the distal stump involving all of its constituents and leading to a breakdown of the axons and their myelin sheaths. This process was first studied by Waller (1852) and is generally known as " Wallerian degeneration ". The first part of Waller's law states that after cutting a nerve degeneration occurs in the distal stump and that degeneration is due to disconnection of the nerve trunk from its " trophic " centre, i.e., the nerve cell.Although it is almost 100 years since this law was conceived, the mechanism of degeneration is still not clear. In order to understand the process it is necessary to investigate the nature of this " trophic influence ". Only in this way can the question, Why does a nerve fibre degenerate ? be solved.Wallerian degeneration results after a certain time in failure of transmission of nerve impulses. The time at which this failure of transmission of nerve impulses can be recorded is apparently not a constant value. It is for instance known that both the metabolic rate and temperature influence the rate of degeneration (Muralt, 1945). Additional information about the factors affecting the rate of degeneration should help in understanding the mechanism of "Wallerian degeneration".It is necessary first to define clearly the criteria of degeneration used. After nerve section degeneration in the physiological sense appears primarily when the nerve fibre will no longer transmit impulses. As a physiological criterion we are therefore using the time at which failure of transmission of nerve impulses can be recorded. A much more complicated problem is the evaluation of the criteria of degeneration in the morphological sense. Muralt (1945) (Johnson, McNabb, and Rossiter, 1949). Valuable quantitative criteria are given by the changes of acetylcholine content in the degenerating nerve (Muralt and Schulthess, 1944), or of cholinesterase content in the degenerating nerve (Sawyer, 1946). Data about enzyme activity in a degenerating nerve will certainly acquire great importance.In this paper we have used physiological and morphological criteria in an attempt to study quantitatively the factors which affect degeneration of peripheral nerve fibres. Methods Rabbits, guinea-pigs, and rats were used in our experiments. In rabbits the peroneal, tibial and, in some experiments, the sural, nerves were used, whereas in rats and guinea-pigs the experiments were done with the whole sciatic nerve. The nerves were cut at an initial operation and, at different times after nerve section, the wounds were reopened and the nerves excised. The excised nerves were placed on platinum electrodes in a thermostat. The temperature of the chamber varied from 36 to 380 C. but was approximately constant for any

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“…How this could occur is not at all clear, but the action of calcium on the membrane is one which would seem to be worth exploring. Other interesting lines of attack are those concerned with the role of acetylcholine (Nachmansohn, I 946), adenosinetriphosphate (Libet, 1948) and thiamine (von Muralt, 1945). '…”

Section: The Nature Of the Permeability Changesmentioning

confidence: 99%

The Ionic Basis of Electrical Activity in Nerve and Muscle

1951

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SUMMARY Four methods of determining the potential difference across the surface membrane of living cells are described. In a wide range of excitable tissues the resting membrane potential is of the order of 50–100 mV. and the action potential of the order of 80–130 mV. At the height of activity the potential difference across the membrane is reversed by 30–50 mV. The potassium concentration inside most excitable cells is 20–50 times greater than that in the external medium; sodium is 3–15 times more concentrated outside than it is inside, while chloride is 5–50 times more concentrated outside than inside. Isolated fibres lose potassium and gain sodium and chloride ions. Potassium appears to exist as a free ion inside nerve and muscle fibres. The nature of the organic anions which balance the high concentration of potassium inside excitable cells is still largely unknown. In certain cases amino‐acids such as aspartic acid are present in high concentrations. The resting membrane behaves as though it were moderately permeable to K+ and Cl‐ but sparingly permeable to Na+. The absolute magnitude of the resting potential is similar to that calculated from the potassium concentrations if allowance is made for the contributions of chloride and other ions. Movements of K+ and Cl‐ as determined by radioactive tracers or by chemical methods agree with a quantitative formulation of this hypothesis. It is necessary to suppose that sodium is continuously pumped out of excitable cells by a process which depends on metabolism. Electrical activity is due to a large and specific increase in the permeability to sodium. The reversed potential difference across the active membrane arises from the concentration difference of sodium and varies with the external concentration of sodium in the same manner as the theoretical potential of a sodium electrode. In many cells, conduction of impulses is impossible if the external medium does not contain sodium or lithium ions. The rate of rise of the action potential varies with the concentration of sodium ions in the external medium. Sodium enters a nerve fibre when it is active. The quantity entering 1 cm.2 of membrane during one impulse is of the order of 3 μμmol. Entry of sodium is approximately balanced by the leakage of a corresponding quantity of potassium. It is suggested that sodium enters the nerve fibre during the rising phase of the action potential and that potassium leaves during the falling phase. The permeability changes during the action potential probably consist of a rapid but transient increase in the permeability to sodium and a delayed increase in the permeability to potassium. It is suggested that both permeability changes vary with membrane potential in a graded but reversible manner. This hypothesis is applied to the phenomena of subthreshold activity, accomodation and oscillatory behaviour. In vertebrate myelinated fibres there is much evidence to show that conduction is saltatory; this suggests that sodium entry is confined to the nodes of Ranvier, and that the inte...

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Die Signalübermittlung im Nerven

Cited by 45 publications

References 0 publications

Evidence for saltatory conduction in peripheral myelinated nerve fibres

Evidence for saltatory conduction in peripheral myelinated nerve fibres

The Degeneration of Peripheral Nerve Fibres

The Ionic Basis of Electrical Activity in Nerve and Muscle

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