Action potential

An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells. In neurons, action potentials play a central role in cell–cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In

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Mechanoelectric feedback in cardiomyocyte monolayers and whole hearts in response to stretch

Barbara Murienne

Stretch has been shown to induce electrophysiological changes in the whole heart and cardiomyocyte monolayer models. However, the mechano-electric mechanisms responsible for these changes are still not completely understood. In this project, micropatterned cardiomyocyte monolayers were anisotropically stretched in order to investigate two hypotheses: the increase in action potential duration (APD) and decrease in conduction velocity (CV) in response to stretch and the effect of stretch-activated channel blockers on these electrophysiological changes. The results obtained showed a decrease in APD in response to stretch in all experiments. Regarding CV, a decrease during propagation in the longitudinal direction (along the long axis of the aligned cardiomyocytes) and an increase during propagation in the transverse direction (along the short axis of the aligned cardiomyocytes) were observed in response to stretch. These electrophysiological changes did not seem altered by the presence of 70 μM and 85 μM streptomycin. However, the results for the APD have to be considered with caution due to limitations of the data analysis procedure

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Homeostatic regulation of axonal Kv1.1 channels accounts for both synaptic and intrinsic modifications in the hippocampal CA3 circuit

Mickael Maurice Zbili

Homeostatic plasticity of intrinsic excitability goes hand in hand with homeostatic plasticity of synaptic transmission. However, the mechanisms linking the two forms of homeostatic regulation have not been identified so far. Using electrophysiological, imaging, and immunohistochemical techniques, we show here that blockade of excitatory synaptic receptors for 2 to 3 d induces an up-regulation of both synaptic transmission at CA3-CA3 connections and intrinsic excitability of CA3 pyramidal neurons. Intrinsic plasticity was found to be mediated by a reduction of Kv1.1 channel density at the axon initial segment. In activity-deprived circuits, CA3-CA3 synapses were found to express a high release probability, an insensitivity to dendrotoxin, and a lack of depolarization-induced presynaptic facilitation, indicating a reduction in presynaptic Kv1.1 function. Further support for the down-regulation of axonal Kv1.1 channels in activity-deprived neurons was the broadening of action potentials measured in the axon. We conclude that regulation of the axonal Kv1.1 channel constitutes a major mechanism linking intrinsic excitability and synaptic strength that accounts for the functional synergy existing between homeostatic regulation of intrinsic excitability and synaptic transmission.

NATL ACAD SCIENCES2021

Numerical methods for nonlinear reaction-diffusion equations with traveling wave solutions

Antoine Giovanni Imboden

In this report, we first introduce operator splitting as a way to solve nonlinear reaction-diffusion PDEs. We then present a flux-limiting technique for anisotropic diffusion problems that allows to recover the discrete maximum principle. Finally, we implement a simple action potential model, which allows us to represent the evolution of the transmembrane potential of a stimulated cell, and investigate the effect of anisotropic diffusion on the positivity of this potential.

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Neuron

Within a nervous system, a neuron, neurone, or nerve cell is an electrically excitable cell that fires electric signals called action potentials across a neural network. Neurons communicate with othe

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An axon (from Greek ἄξων áxōn, axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts ele

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