The patient with acute neurological problems
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
A nerve impulse, or action potential, is a series of electrical events that take place sequentially along the length of an axon. An action potential has two phases: depolarisation and repolarisation. When a neurone is stimulated, sodium ions (Na+) flow rapidly across the initial segment and into the cytoplasm of the axon: this is depolarisation. Depolarisation changes the electrical charge of that section of the axon causing potassium ions (K+) to flow rapidly out of the axon and into the interstitial space: this is repolarisation. The sequential depolarisation and repolarisation of the axon cell membrane is like a row of dominoes; once the first action potential has occurred it causes neighbouring sections of the membrane to depolarise. The Na+/K+ pump on the axon cell membrane ensures the Na+ and K+ ions are restored to their normal positions, ready for the next action potential to occur (see Figure 9.5).
The patient with acute neurological problems
Ian Peate, Helen Dutton in Acute Nursing Care, 2014
A nerve impulse, or action potential, is a series of electrical events that take place sequentially along the length of an axon. An action potential has two phases: depolarisation and repolarisation. When a neurone is stimulated sodium ions (Na+) flow rapidly across the initial segment and into the cytoplasm of the axon: this is depolarisation. Depolarisation changes the electrical charge of that section of the axon causing potassium ions (K+) to flow rapidly out of the axon and into the interstitial space: this is repolarisation. The sequential depolarisation and repolarisation of the axon cell membrane is like a row of dominoes, once the first action potential has occurred it causes neighbouring sections of the membrane to depolarise. The Na+/K+ pump on the axon cell membrane ensures the Na+ and K+ ions are restored to their normal positions ready for the next action potential to occur (see Figure 9.5).
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
A molecule or ATOM that is electrically charged, having either gained or lost electrons. A CATION has a positive charge, an ANION has a negative charge. In solution many substances break down into their component parts: common salt—sodium chloride (NaCl)—for example breaks down in water into positively charged sodium ions (Na+) and negatively charged chloride ions (Cl ). The relative balance of positively and negatively charged ions on either side of a neuronal MEMBRANE determines the RESTING POTENTIAL of a NEURON. The movement of ions across the membrane is critical for ACTION POTENTIAL generation. Movement of ions across a membrane can be a RECEPTOR-mediated process, occurring via the receptor-regulated ION CHANNEL system, or a process mediated by specialized transport mechanisms such as the SODIUM-POTASSIUM PUMP and the CALCIUM PUMP.
QT shortening: a proarrhythmic safety surrogate measure or an inappropriate indicator of it?
Published in Current Medical Research and Opinion, 2022
Amy Tanti, Benjamin Micallef, Janis Vella Szijj, Anthony Serracino-Inglott, John-Joseph Borg
Within excitable cardiac cells, an electrical stimulus causes the transmembrane voltage to experience a brief change known as an action potential (AP)1. The action potential duration (APD) is defined as the amount of time in which the voltage remains elevated above the resting membrane voltage2. The QT interval represents the time of ventricular activity and is measured from the beginning of the QRS complex to the end of the T wave and reflects the APD3. The QT interval should be corrected for heart rate (QTc) to enable comparison with reference values3. The QTc is normally between 350 and 460 milliseconds (ms) and is considered abnormally short if <350 ms4. Concern is emerging about the pro-arrhythmic risk associated with QT interval shortening and congenital short QT syndrome has been recognized as a congenital clinical entity that may trigger potentially fatal tachyarrhythmias5. Hyperfunction of the delayed rectifier potassium current or hypofunction of the calcium current result in a shortening of the repolarization period, an increase in transmural dispersion of repolarization and cause short QT interval, short atrial and ventricular effective refractory periods, and, as a result increase susceptibility to arrhythmias6.
Efficient simulations of stretch growth axon based on improved HH model
Published in Neurological Research, 2023
Xiao Li, Xianxin Dong, Xikai Tu, Hailong Huang
The HH model can accurately interpret the experimental results of electrophysiological activity of squid axons and quantitatively describe the changes in voltage and current on the neuron membrane. Firstly, by changing the concentration of the extracellular ions (mainly sodium and potassium ions), the current carried by the ions is deduced, and then the experimental results are fitted with the mathematical model to solve the mathematical model. By comparing the action potentials of the model with those recorded in the experiment, the correctness of the model is verified. The mechanism of the action potential under electrical stimulation was discovered by Hodgkin and Huxley [4]. When nerve cells are stimulated with adequate excitatory current, the cell membrane potential rises and the permeability of the cell membrane changes, allowing a huge amount of sodium ions to influx, raising the membrane potential even higher and producing an action potential. Potassium ions began to flow out in huge quantities when the membrane potential reached its peak value, causing the membrane potential to drop until it reverted to its resting condition. Cell depolarization above the threshold, according to Hodgkin and Bernard Katz [5], causes a brief increase in the permeability of the cell membrane to sodium ions. The permeability of sodium ions outweighed the permeability of potassium ions throughout this time. This establishes a research foundation for the development of axon action potentials in response to mechanical traction.
Acoustic simulation of cochlear implant hearing: Effect of manipulating various acoustic parameters on intelligibility of speech
Published in Cochlear Implants International, 2018
Saransh Jain, P.G. Vipin Ghosh
The sentences were simulated using the cochlear implant simulation (ver. 2.0) software (Vega et al., 2004). The simulation program was based on an analysis–synthesis model. The sentences were first recorded using the windows sound recorder at the sampling rate of 44,100 Hz. The recorded acoustic signal was imported to the cochlear implant simulation software. The analysis block of the simulator processed the acoustic signal and transformed into patterns of stimulation pulses. The impulses were generated in the way as different electrodes in the implant generate them, which in turn mimics the generation of action potential in the auditory nerve. The sentence pulses were then sent to the synthesis block where the signal was synthesized using the patterns of activities corresponding to each frequency band along the length of the cochlea. This synthesis process modifies the acoustic signal in such a way that multiple parameters, such as stimulation rate, frequency filter, envelope extraction strategy, number of channels and channels stimulated per cycle, size of the electrode array, and interaction between various electrodes and neural ends, can be conditioned. The simulation software modifies the audio signal as per some set parameters determined by the user. The pattern of neural activity at each cochlear portion was considered and the synchronizing capability of the neural activity and the characteristic frequency of the simulated cochlear implant were generated.
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