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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.
Occupational toxicology of the nervous system
Published in Chris Winder, Neill Stacey, Occupational Toxicology, 2004
The main function of the nerve is the transmission of nerve impulses. Nervous impulses are electrochemical events initiated by various stimuli.Alterations in membrane permeability cause sodium ions to enter the cell.The resting charge on the cell changes (depolarisation).A wave of depolarisation spreads over the surface of the cell, and down the axon.Resting state cell charge is restored by the diffusion of potassium ions out of the cell (repolarisation).The wave of neurotransmission will produce a range of effects depending on the effector system at the end of the axon.
Electric Activities of the Cell
Published in Kayvan Najarian, Robert Splinter, Biomedical Signal and Image Processing, 2016
Kayvan Najarian, Robert Splinter
The depolarization stage continues until the maximum positive potential is reached after which the cell starts a stage called “repolarization.” Specifically, at the end of depolarization stage, the positive potential opens a number of potassium channels that allow the potassium ions residing inside the cell leave the cell. This process reduces the potential difference continuously. At a certain point in time, so many potassium ions have left the cell that the potential difference becomes negative, i.e., the cell repolarizes. The changes in permeability of the sodium channels are also shown in Figure 8.4.
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.
Objective stress monitoring based on wearable sensors in everyday settings
Published in Journal of Medical Engineering & Technology, 2020
Hee Jeong Han, Sina Labbaf, Jessica L. Borelli, Nikil Dutt, Amir M. Rahmani
ECG is a measure of the electrical activity of the heart during each cardiac cycle [15]. The ECG uses electrodes to measure electrical signals produced by depolarisation and repolarization of the heart [16]. A typical heart rate consists of a P wave, a QRS complex, and a T wave. The R-R interval is the time interval between adjacent R peaks in the ECG [14]. Heart rate (HR) and heart rate variability (HRV) are calculated from the R-R interval.
Reconstruction of cardiac activities from Vectorcardiography and Magnetocardiography using Bayesian approach with coherence mapping
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2021
The cardiac conduction starts with a flow of tiny currents in the myocardial cells due to ionic exchange that creates a potential difference across the membrane called as transmembrane potential (tmp). Each cardiac cell undergoes a change in potential from −90 mV (resting potential) to 10 mV called as depolarisation phase and back to resting potential called repolarisation stage. The timing and phase activities of each cardiac cell varies. These electrical impulses reach covers each and every myocardial muscle fibre helping them to contract and relax. The excitation activities of a cell can be represented in the form of small current segments. The sum of activation waves reaches the body surface forming a functional wave that characterises to P, QRS and T (Pullan et al. 2005). P wave is formed due to depolarisation of atrium, whereas QRS is created due to contraction of ventricles. Finally, repolarisation of ventricles results in T wave. These electrophysiological changes represent the functioning of the heart are usually measured as potentials and magnetic field by Electrocardiogram (ECG) and Magnetocardiogram (MCG) respectively. The deviations from the normal functioning waves impressed/recorded in E/MCG detectors exhibit cardiac dysfunctions. Although ECG compromises to diagnose functionality of the heart, it lacks its ability to localise the abnormalities effectively. In order to assess such anomalies, clinicians have to either examine with invasive procedures or obtain structural information. MCG offers distinct advantages than ECG in such a way that, it is unaffected by skin conductivity profiles and also is a non-contact technique. Due to this reason, MCG has more localisation accuracy than ECG. Many researchers have contributed their works in localisation of cardiac sources non-invasively using bioelectric fields. Cardio-magnetic imaging is an emerging technology in the biomedical society that promises to evaluate many cardiac-related diseases without invasive procedures.