scholarly journals Physical model of electrical synapses in a neural network

2021 ◽  
Author(s):  
Mikhail Pekker ◽  
Mikhail Shneider
Keyword(s):  
Neural Network ◽  
Theoretical Model ◽  
Action Potential ◽  
Physical Model ◽  
Nodes Of Ranvier ◽  
Myelinated Axons ◽  
Active Neuron ◽  
Electrical Synapses ◽  
Ephaptic Coupling

A theoretical model of electrical synapses is proposed, in which connexons play the role of nails that hold unmyelinated areas of neurons at a distance of about 3.5 nm, and the electrical connection between them is provided by charging the membrane of an inactive neuron with currents generated in the intercellular electrolyte (saline) by the action potential in the active neuron. This mechanism is similar to the salutatory conduction of the action potential between the nodes of Ranvier in myelinated axons and the ephaptic coupling of sufficiently close spaced neurons.

scholarly journals New plasmon-polariton model of the saltatory conduction

2020 ◽  
Author(s):  
W. A. Jacak
Keyword(s):  
Nervous System ◽  
Action Potential ◽  
Unmyelinated Axon ◽  
Myelinated Axons ◽  
Ion Density ◽  
Cable Theory ◽  
Unmyelinated Axons ◽  
Saltatory Conduction ◽  
Plasmon Polariton

ABSTRACTWe propose a new model of the saltatory conduction in myelinated axons. This conduction of the action potential in myelinated axons does not agree with the conventional cable theory, though the latter has satisfactorily explained the electrosignaling in dendrites and in unmyelinated axons. By the development of the wave-type concept of ionic plasmon-polariton kinetics in axon cytosol we have achieved an agreement of the model with observed properties of the saltatory conduction. Some resulting consequences of the different electricity model in the white and the gray matter for nervous system organization have been also outlined.SIGNIFICANCEMost of axons in peripheral nervous system and in white matter of brain and spinal cord are myelinated with the action potential kinetics speed two orders greater than in dendrites and in unmyelinated axons. A decrease of the saltatory conduction velocity by only 10% ceases body functioning. Conventional cable theory, useful for dendrites and unmyelinated axon, does not explain the saltatory conduction (discrepancy between the speed assessed and the observed one is of one order of the magnitude). We propose a new nonlocal collective mechanism of ion density oscillations synchronized in the chain of myelinated segments of plasmon-polariton type, which is consistent with observations. This model explains the role of the myelin in other way than was previously thought.

scholarly journals Predicting the Influence of Axon Myelination on Sound Localization Precision Using a Spiking Neural Network Model of Auditory Brainstem

2021 ◽  
Author(s):  
Ben-Zheng Li ◽  
Sio Hang Pun ◽  
Mang I Vai ◽  
Tim Lei ◽  
Achim Klug
Keyword(s):  
Neural Network ◽  
Action Potential ◽  
Network Model ◽  
Sound Localization ◽  
Neural Network Model ◽  
Auditory Brainstem ◽  
Spiking Neural Network ◽  
Medial Superior Olive ◽  
Myelinated Axons ◽  
Spiking Neural Network Model

Spatial hearing allows animals to rapidly detect and localize auditory events in the surrounding environment. The auditory brainstem plays a central role in processing and extracting binaural spatial cues through microsecond-precise binaural integration, especially for detecting interaural time differences (ITDs) of low-frequency sounds at the medial superior olive (MSO). A series of mechanisms exist in the underlying neural circuits for preserving accurate action potential timing across multiple fibers, synapses and nuclei along this pathway. One of these is the myelination of afferent fibers that ensures reliable and temporally precise action potential propagation in the axon. There are several reports of fine-tuned myelination patterns in the MSO circuit, but how specifically myelination influences the precision of sound localization remains incompletely understood. Here we present a spiking neural network model of the auditory brainstem with myelinated axons to investigate whether different axon myelination thicknesses alter the sound localization process. Our model demonstrates that axon myelin thickness along the contralateral pathways can substantially modulate ITD detection. Furthermore, optimal ITD sensitivity is reached when the MSO receives contralateral inhibition via thicker myelinated axons compared to contralateral excitation, a result that is consistent with previously reported experimental observations. Our results suggest specific roles of axon myelination for extracting temporal dynamics in ITD perception, especially in the pathway of the contralateral inhibition.

ON EVALUATION OF THE ROLE OF THERMAL AND WIND FACTORS FOR A PHYSICAL MODEL OF THE WORLD OCEAN GENERAL CIRCULATION SYSTEM

2019 ◽  
Vol 47 (3) ◽  
pp. 80-91
Author(s):  
V. G. Neiman
Keyword(s):  
Physical Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
World Ocean ◽  
Circulation System ◽  
The Public ◽  
The World ◽  
Almost All ◽  
Conceptual Foundations

The main content of the work consists of certain systematization and addition of longexisting, but eventually deformed and partly lost qualitative ideas about the role of thermal and wind factors that determine the physical mechanism of the World Ocean’s General Circulation System (OGCS). It is noted that the conceptual foundations of the theory of the OGCS in one form or another are contained in the works of many well-known hydrophysicists of the last century, but the aggregate, logically coherent description of the key factors determining the physical model of the OGCS in the public literature is not so easy to find. An attempt is made to clarify and concretize some general ideas about the two key blocks that form the basis of an adequate physical model of the system of oceanic water masses motion in a climatic scale. Attention is drawn to the fact that when analyzing the OGCS it is necessary to take into account not only immediate but also indirect effects of thermal and wind factors on the ocean surface. In conclusion, it is noted that, in the end, by the uneven flow of heat to the surface of the ocean can be explained the nature of both external and almost all internal factors, in one way or another contributing to the excitation of the general, or climatic, ocean circulation.

Transition Times in Memory

2018 ◽  
Author(s):  
Donatella della Porta ◽  
Massimiliano Andretta ◽  
Tiago Fernandes ◽  
Eduardo Romanos ◽  
Markos Vogiatzoglou
Keyword(s):  
Theoretical Model ◽  
Social Movement ◽  
Transition Period ◽  
Two Dimensions ◽  
Democratic Regime ◽  
Organizational Models ◽  
Different Types ◽  
Transition Times ◽  
Movement Participation

The second chapter covers the main characteristics of transition time in the four countries: Italy, Greece, Spain, and Portugal. After developing the theoretical model on paths of transition, with a focus on social movement participation, the chapter looks at social movements and protest events as turning points during transition, covering in particular the specific movement actors, their organizational models, and their repertoires of action and frames. The chapter focuses on two dimensions: the role of mobilization in the transition period, which implies the analysis of how elites and masses interact, ally, or fight with each other in the process, and the outcome of transitions as continuity versus rupture of the democratic regime vis-à-vis the old one. It concludes by elaborating some hypotheses on how different modes of transition may produce different types and uses of (transition) memories.

scholarly journals Implication of Contactins in Demyelinating Pathologies

Life ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 51
Author(s):  
Ilias Kalafatakis ◽  
Maria Savvaki ◽  
Theodora Velona ◽  
Domna Karagogeos
Keyword(s):  
Nervous System ◽  
White Matter ◽  
Cell Adhesion Molecules ◽  
White Matter Lesions ◽  
Myelinated Axon ◽  
Immunoglobulin Superfamily ◽  
Proper Function ◽  
Myelinated Axons ◽  
And Function

Demyelinating pathologies comprise of a variety of conditions where either central or peripheral myelin is attacked, resulting in white matter lesions and neurodegeneration. Myelinated axons are organized into molecularly distinct domains, and this segregation is crucial for their proper function. These defined domains are differentially affected at the different stages of demyelination as well as at the lesion and perilesion sites. Among the main players in myelinated axon organization are proteins of the contactin (CNTN) group of the immunoglobulin superfamily (IgSF) of cell adhesion molecules, namely Contactin-1 and Contactin-2 (CNTN1, CNTN2). The two contactins perform their functions through intermolecular interactions, which are crucial for myelinated axon integrity and functionality. In this review, we focus on the implication of these two molecules as well as their interactors in demyelinating pathologies in humans. At first, we describe the organization and function of myelinated axons in the central (CNS) and the peripheral (PNS) nervous system, further analyzing the role of CNTN1 and CNTN2 as well as their interactors in myelination. In the last section, studies showing the correlation of the two contactins with demyelinating pathologies are reviewed, highlighting the importance of these recognition molecules in shaping the function of the nervous system in multiple ways.

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