A model of the electrical behaviour of myelinated sensory nerve fibres based on human data

Abstract

Page 233 Last sentence before '4.2 Implications for SCS modelling': "The results show that the behaviour of the new model for human myelinated sensory nerve fibres corresponds substantially better with the properties measured for this type of human nerve fibre than other fibre models do.".

Modelled temperature-dependent excitability behaviour of a single ranvier node for a human peripheral sensory nerve fibre

“…This value was further optimised until the simulated action potential's recovery phase resembled those of the Schwarz study's action potential. Estimating a Na + concentration ratio (Na cr ) proved difficult, with previously reported values ranging from 4.4 to 14.05 (Scholz et al 1993; Atkins (1995) Faraday constant (F) 9 .6485 × 10 4 C/mol Atkins (1995) Hodgkin and Huxley (1952), Schwarz et al (1995), Wesselink et al (1999), Reid et al (1993), Scholz et al (1993), Schwarz et al (1995) Scholz et al (1993), Schwarz et al (1995) Schwarz et al 1995;Wesselink et al 1999;Hille 2001). The value therefore had to be optimised for the model and this turned out to be only slightly higher than the original HH model value of 6.48 (Table 2).…”

“…Also, the conductances of ion channels increase very little with a temperature increase, with Q 10 factors typically in the vicinity of the values for aqueous diffusion; ranging from 1.0 to 1.6 in most cases (Hille 2001). The values for g Na and its Q 10 factor played an important role in determining the action potential amplitude and were optimised by comparison with the calculated amplitudes at 20, 25 and 37 • C from Wesselink et al (1999). To measure the time course and voltage dependence of activation and inactivation characteristics for ionic membrane currents, the current amplitude has to be sufficiently large so that it can be detected (Schwarz et al 2006).…”

“…Both Schwarz et al (1995) and Wesselink et al (1999) used a reference temperature (T 0 ) of 20 • C, while Hodgkin and Huxley (1952) used a reference temperature (T 0 ) of 6.3 • C. To aid comparison with these models, the reference temperature for the new nodal model was changed to 20 • C. Optimisation of parameters was performed at this temperature and the action potential shape and amplitude compared to the corresponding estimated data from the aforementioned studies. Next, the temperature dependence of the rate equations, as expressed through Q 10 factors, was determined by comparing simulated and estimated action potential shapes and amplitudes at 25 and 37 • C (Table 1).…”

“…Schwarz et al (1995) measured ionic membrane currents and action potentials at Ranvier nodes from partially demyelinated human peripheral sensory nerve fibres, but no morphometric nerve fibre data were supplied. Wesselink et al (1999) estimated the action potential rise and fall times and amplitudes at 20 and 25 • C from the aforementioned study, as well as predicted values at 37 • C, and these values were used for the nodal model validation.…”

“…Studies on human peripheral nerve fibres indicate an increase in action potential amplitude and duration, the absolute and relative refractory periods and chronaxie times when the temperature is decreased from 37 • C; while the rheobase current and conduction velocity decrease under the same temperature conditions (Buchthal and Rosenfalck 1966;Lowitzsch et al 1977;Kiernan et al 2001). Temperature dependence of the sodium channel kinetics is included in computational models describing excitation behaviour in human nerve fibres; for example the models of Schwarz et al (1995) and Wesselink et al (1999), but not so for the potassium channel and leakage kinetics, as well as other electrical parameters used. Similar to the HH model, temperature dependency of rate constants is effected using Q 10 factors.…”