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Large-Scale Finite Element Analysis of the Beating Heart
Published in Theo C. Pilkington, Bruce Loftis, Joe F. Thompson, Savio L-Y. Woo, Thomas C. Palmer, Thomas F. Budinger, High-Performance Computing in Biomedical Research, 2020
Andrew McCulloch, Julius Guccione, Lewis Waldman, Jack Rogers
Cardiac cells are electrically excitable and tightly coupled to each other. With a sufficiently strong electrical stimulus, the myocyte, which normally supports a negative transmembrane potential gradient at rest, may be transiently depolarized. The time course of excitation and recovery during this cardiac “action potential” is governed by ionic currents which flow across the membrane through specialized voltage-dependent ion channels specific to various ionic species, especially sodium, potassium, and calcium. Following the rapid onset of the action potential, a subsequent stimulus will fail to elicit another response until the cell has recovered sufficiently; this interval is called the absolute refractory period. During the “relative refractory period,” subsequent action potentials can be evoked, but the threshold stimulus is raised.
Axon-Inspired Communication Systems
Published in James E. Morris, Krzysztof Iniewski, Nanoelectronic Device Applications Handbook, 2017
Valeriu Beiu, Liren Zhang, Azam Beg, Walid Ibrahim, Mihai Tache
When a neuron is stimulated, the voltage-gated Na+ channels open and the Na+ ions start flowing into the cell. This causes a local increase of the membrane potential, which in turn activates neighboring voltage-gated Na+ channels, which also open. The resulting local depolarization also stimulates nearby voltage-gated K+ channels to also open. Therefore, K+ ions start flowing out of the cell in a process called repolarization. Still, even before the Na+ and K+ ions across the membrane equilibrate, both the Na+ and K+ channels close automatically after a very brief period of time (resting). The main result of these timely orchestrated actions of large numbers of voltage-gated ion channels is a local and moving reversal of the membrane potential, which is known as an action potential (Figure 15.3b). In the end, K+ ions move outside and restore the resting potential. The resulting “spikes” are the ones representing and propagating information along an axon. After an action potential has taken place, there is a period of time (known as the refractory period) during which the membrane cannot be stimulated again.
A Review of the Technologies and Methodologies Used to Quantify Muscle-Tendon Structure and Function
Published in Cornelius Leondes, Musculoskeletal Models and Techniques, 2001
The number of receptors that must be stimulated to cause these changes varies for different fiber types. Permeability changes cause sodium ions to enter the cell and potassium ions to leave the cell. The membrane depolarizes, becoming less negative inside the cell. The signal, or action potential, is propagated in both directions along the length of the muscle fiber. An action potential is always the same for a given cell. The cell depolarizes in an all-or-none response once a sufficient stimulus is achieved. After the action potential, there is a refractory period in which the cell cannot be activated again. The refractory period is necessary to prevent back flow of impulses.
Emerging memristive neurons for neuromorphic computing and sensing
Published in Science and Technology of Advanced Materials, 2023
Zhiyuan Li, Wei Tang, Beining Zhang, Rui Yang, Xiangshui Miao
The working process of biological neurons involves complex ion dynamics processes. The neuronal membrane serves as a barrier between the external environment and the neuronal cytoplasm, across which various ion exchange processes take place. These processes are in turn governed by voltage-dependent opening and closing of ion channels (e.g. Na+ and K+ ion channels) [46,47]. As illustrated in Figure 1(b), an action potential can normally be roughly divided into four segments: resting potential, depolarization, repolarization, and hyperpolarization. Initially, the neuron is in a resting potential (usually ~−70 mV), the membrane potential maintains a constant charge gradient (Na+/K+ pump). When incoming spikes induce the membrane potential to reach the threshold of the neuron (usually ~−55 mV), Na+ ion channels are activated, and the rapid influx of Na+ ions results in depolarization of the membrane potential. Then, the voltage-gated K+ ions channels determine physiological processes of repolarization and hyperpolarization. Ion pumps allow K+ ions to flow out of the cell membrane, the membrane potential decreases rapidly, until it reaches a new resting state when the outward of K+ ions balance the inward of Na+ ions. This spike generation process is an all-or-none event, a spike generates when its membrane potential exceeds the threshold; Otherwise, the membrane potential boosting lasts for a short time without leading to spike generation. Note that after the neuron emitting an action potential, it remains nonresponsive to subsequent stimuli for a certain period of time, called as the refractory period.
Deep spatio-temporal sparse decomposition for trend prediction and anomaly detection in cardiac electrical conduction
Published in IISE Transactions on Healthcare Systems Engineering, 2022
Xinyu Zhao, Hao Yan, Zhiyong Hu, Dongping Du
In both cases, every other stimulation dies out and does not propagate like others. This is due to the refractoriness of the cardiac cell, where immediate stimulation after repolarization within in the cell refractory period cannot be initiated. The refractoriness of the cardiac cell can change the propagating direction when two waves merge together, as seen in the right case. It is essential to model such refractoriness to capture the complex and dynamic activities of cardiac electrical waves. Besides the regular stimulation, there are also signals caused by irregular stimulations due to the malfunction of the cardiac cells.