scholarly journals Density of sodium channels in mammalian myelinated nerve fibers and nature of the axonal membrane under the myelin sheath.

1977 ◽  
Vol 74 (1) ◽  
pp. 211-215 ◽  
Author(s):  
J. M. Ritchie ◽  
R. B. Rogart
Keyword(s):  
Sodium Channels ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Axonal Membrane ◽  
Myelinated Nerve Fibers

Computer Model for Action Potential Propagation Through Branch Point in Myelinated Nerves

2001 ◽  
Vol 85 (1) ◽  
pp. 197-210 ◽  
Author(s):  
Lei Zhou ◽  
Shing Yan Chiu
Keyword(s):  
Action Potential ◽  
Branch Point ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Axonal Membrane ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Action Potential Propagation ◽  
Periaxonal Space

A mathematical model is developed for simulation of action potential propagation through a single branch point of a myelinated nerve fiber with a parent branch bifurcating into two identical daughter branches. This model is based on a previously published multi-layer compartmental model for single unbranched myelinated nerve fibers. Essential modifications were made to couple both daughter branches to the parent branch. There are two major features in this model. First, the model could incorporate detailed geometrical parameters for the myelin sheath and the axon, accomplished by dividing both structures into many segments. Second, each segment has two layers, the myelin sheath and the axonal membrane, allowing voltages of intra-axonal space and periaxonal space to be calculated separately. In this model, K ion concentration in the periaxonal space is dynamically linked to the activity of axonal fast K channels underneath the myelin in the paranodal region. Our model demonstrates that the branch point acts like a low-pass filter, blocking high-frequency transmission from the parent to the daughter branches. Theoretical analysis showed that the cutoff frequency for transmission through the branch point is determined by temperature, local K ion accumulation, width of the periaxonal space, and internodal lengths at the vicinity of the branch point. Our result is consistent with empirical findings of irregular spacing of nodes of Ranvier at axon abors, suggesting that branch points of myelinated axons play important roles in signal integration in an axonal tree.

scholarly journals Pharmacological Modifications of the Sodium Channels of Frog Nerve

1968 ◽  
Vol 51 (2) ◽  
pp. 199-219 ◽  
Author(s):  
Bertil Hille
Keyword(s):  
Sodium Channels ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Apparent Dissociation Constant ◽  
Specific Change ◽  
Myelinated Nerve Fibers ◽  
Sodium Activation ◽  
Sodium Inactivation ◽  
Na Ions ◽  
Ionic Forms

Voltage clamp measurements on myelinated nerve fibers show that tetrodotoxin, saxitoxin, and DDT specifically affect the sodium channels of the membrane. Tetrodotoxin and saxitoxin render the sodium channels impermeable to Na ions and to Li ions and probably prevent the opening of individual sodium channels when one toxin molecule binds to a channel. The apparent dissociation constant of the inhibitory complex is about 1 nM for the cationic forms of both toxins. The zwitter ionic forms are much less potent. On the other hand, DDT causes a fraction of the sodium channels that open during a depolarization to remain open for a longer time than is normal. The effect cannot be described as a specific change in sodium inactivation or as a specific change in sodium activation, for both processes continue to govern the opening of the sodium channels and neither process is able to close the channels. The effects of DDT are very similar to those of veratrine.

scholarly journals THE ULTRASTRUCTURE OF ADULT VERTEBRATE PERIPHERAL MYELINATED NERVE FIBERS IN RELATION TO MYELINOGENESIS

1955 ◽  
Vol 1 (4) ◽  
pp. 271-278 ◽  
Author(s):  
J. David Robertson
Keyword(s):  
Electron Microscope ◽  
Schwann Cell ◽  
Cell Surface ◽  
Peripheral Nerve ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Myelinated Nerve ◽  
Thin Sections ◽  
Double Membrane ◽  
Myelinated Nerve Fibers

Adult chameleon myelinated peripheral nerve fibers have been studied with the electron microscope in thin sections. The outer lamella of the myelin sheath has been found to be connected as a double membrane to the surface of the Schwann cell. The inner lamella is connected as a similar double membrane with the double axon-Schwann membrane. The relations of these double connecting membranes suggest that the layered myelin structure is composed of a double membrane which is closely wound about the axon as a helix. These findings support the new theory of myelinogenesis proposed recently by Geren. The possible significance of these results with respect to cell surface membranes and cytoplasmic double membranes is discussed.

Nodal swelling produced by ciguatoxin-induced selective activation of sodium channels in myelinated nerve fibers

Neuroscience ◽  
1996 ◽  
Vol 71 (4) ◽  
pp. 1121-1131 ◽  
Author(s):  
E. Benoit ◽  
P. Juzans ◽  
A.-M. Legrand ◽  
J. Molgo
Keyword(s):  
Sodium Channels ◽  
Nerve Fibers ◽  
Selective Activation ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers

scholarly journals STUDIES ON THE PROBLEM OF PRESERVATION OF MYELIN SHEATH ULTRASTRUCTURE: EVALUATION OF FIXATION, DEHYDRATION, AND EMBEDDING TECHNIQUES

1961 ◽  
Vol 9 (2) ◽  
pp. 429-443 ◽  
Author(s):  
Richard M. Condie ◽  
A. Ervin Howell ◽  
Robert A. Good
Keyword(s):  
Electron Microscopy ◽  
Myelin Sheath ◽  
Nerve Fibers ◽  
Nerve Tissue ◽  
Tissue Preparation ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Fixation Techniques ◽  
Myelinated Nerves ◽  
Embedding Methods

Currently accepted methods of tissue preparation for electron microscopy result in alterations of myelinated nerve fibers. In an attempt to minimize distortion of myelin, various fixation techniques, dehydration schedules, and embedding methods have been evaluated. It was found that the major damage to myelinated nerves occurs in the embedding procedure. A technique for embedding nerve tissue using the polyester Vestopal W is described which was found to result in improved preservation of myelin.

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