The nervous system is the body's fundamental communication system, enabling rapid and coordinated transmission of information via action potentials – short-lasting changes in membrane potential initiated by appropriate stimuli. Modelling of nerve cells is crutial for understanding the complex electrophysiological processes that occur when neurons are exposed to external electric fields and currents. Computational and mathematical models, such as the Hodgkin-Huxley model, allow detailed simulation of neuronal responses and the study of various pathological conditions as well as the development and refinement of therapies based on electroporation and functional electrical stimulation.
In my master’s thesis, I implemented the Hodgkin-Huxley model of a nerve cell and a set of 54 stimulation protocols (one monophasic and 53 biphasic) in the Python programming language. Through simulations, I analysed the influence of key protocol parameters: number of pulses (N), pulse phase duration (Tp), interphase pause (d1), and interpulse pause (d2) on the excitation threshold of the neuron.
Simulation results confirm that the waveform of the electrical stimulus significantly affects neuronal excitability and the corresponding action potential threshold. The analysis showed that longer d1 and d2 pauses generally contribute to a lower excitation threshold, whereas a combination of a short d1 and a long d2 lead to a substantial increase in threshold. Notably, protocols with a long interphase pause and short interpulse pause required lower stimulation amplitudes compared to those with the reverse configuration, highlighting the importance of temporal structuring within the stimulation protocol. Furthermore, it was observed that monophasic pulses triggered action potentials at significantly lower current density amplitudes than biphasic pulses.
With very short pulses, a delayed onset of the action potential was observed, attributed to the temporal dynamics of ion channels and their associated time constants.
This thesis contributes to a better understanding of the temporal dynamics of neuronal excitation and the influence of different stimulation parameters on the action potential threshold. The results represent an important step toward the optimization of electrostimulation protocols and provide a foundation for future research aimed at developing safer and more effective therapeutic strategies with reduced risk of undesired side effects.
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