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Brain Dynamics: Neural Systems in Space and Time
Published in Ranjit Kumar Upadhyay, Satteluri R. K. Iyengar, Spatial Dynamics and Pattern Formation in Biological Populations, 2021
Ranjit Kumar Upadhyay, Satteluri R. K. Iyengar
The action potential is produced in the cell body of the neurons and travels as a wave along the axon. The membrane of axon also consists of voltage-gated ion channels as soma’s membrane which allows transmission of electrical impulses. The signals are propagated by different ions carrying the charges. The ionic currents move toward the intracellular medium along the axon when the axon potential is generated, and depolarize the adjacent region of the membrane to evoke an action potential in the neighboring membrane patches. The flow of current passively travels from one Ranvier’s node to another. It increases the conduction velocity of action potential. In an unmyelinated axon, the axon potential propagates continuously along the axon. The signal is propagated from soma to the axon terminal.
Electrophysiology
Published in A. Bakiya, K. Kamalanand, R. L. J. De Britto, Mechano-Electric Correlations in the Human Physiological System, 2021
A. Bakiya, K. Kamalanand, R. L. J. De Britto
Action potentials are the electrical signals that accompany the mechanical contraction of a single cell when stimulated by an electric current (Hammond, 2014). Action potentials are caused by flow of ions across the cell membrane (White, 2002; Hammond, 2014) which provide information on the anatomical structure and physiological functions of the cell. Figure 3.2 shows the typical action potential along with its various parts.
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.
A bulk-driven, buffer-biased, gain-boosted amplifier for biomedical signal enhancement
Published in Cogent Engineering, 2019
Sarin Vijay Mythry, D. Jackuline Moni
Human body has an intricate network which is spread across the body and is controlled by the centers in the Brain and the Spinal cord. It is this nerve network which conveys the action commands from the control centers and in return gathers feedback information from various parts of the body via electro-chemical mechanisms. The unit of this elaborate nerve network is called a neuron. Neuron is a cell which has a cell body, dendrites, and an axon. Neurological and psychiatric disorders might be due to changes in inter-neuron information transfer and changes in the excitability of the neurons. Epilepsy is an example of a disease due to abnormal neuronal excitability. The information is transferred between neurons in the form of electrical signal which result from the flow of chemical ions across the cell membrane through ion channels. There are broadly two types of ion channels; they are leakage channels and voltage-gated channels. The leakage channels are open at rest and influence the cellular resting membrane potential. Voltage-gated channels on the other sideopen and close rapidly creating rapid signals called action potentials. These action potentials are generated near cell body and are transmitted along the axon till the nerve terminal without much decrement due to myelination of axon. At the nerve terminal, the action potential-induced depolarization opens voltage-gated calcium channels, which release chemicals called neuro-transmitters outside the neuron. When the neurotransmitter binds to another neuron it alters its excitability and thereby transferring the information, which is further propagated till its intended end site.
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.
A Functional BCI Model by the P2731 working group: Physiology
Published in Brain-Computer Interfaces, 2021
Ali Hossaini, Davide Valeriani, Chang S. Nam, Raffaele Ferrante, Mufti Mahmud
Alongside an idealized neuron, Figure 5 depicts an oligodendrocyte cell whose branches enclose the axon of a cerebral neuron in a myelin sheath. While myelin is not essential for neural function, it is used in many classes of neurons within and outside the central nervous system to enhance electrical conduction. In the brain, unmyelinated neurons constitute ‘gray matter’ while myelinated neurons are called ‘white matter’ because a mass of fatty myelin has a white appearance [35,36]. Myelin sheaths are punctuated by breaks called Nodes of Ranvier that enable an action potential to propagate efficiently through the length of the axon through a process known as saltatory conduction [37].