Fig. 1. (a) Schematic diagram of a myelinated nerve fibre structure and (b) schematic diagram of the myelinated nerve fibre ion channel distribution.

Fig. 2. Schematic diagram of the model.

Fig. 3. Time-domain waveforms of low-frequency action potentials at different Ranvier’s nodes (The action potential at j = 10, j = 20, and j = 30 Ranvier’s nodes were shown).

Fig. 4. Time-domain waveforms and frequency spectrum of high-frequency electromagnetic fields at points A, B, and C in Fig. 2.

Fig. 5. Waveform of signals at different positions for myelin lengths L → + ∞.

Fig. 6. The waveform of the action potential between two adjacent Ranvier’s nodes when the length of the myelin sheath is finite (panels (a)–(d) indicate that the length of the myelin sheath is 3 mm, 7 mm, 8.3 mm, and 10 mm, respectively, other parameters are set as follows: neuron diameter 5 μm, ambient temperature 10 °C).

Fig. 7. The effect of ion channel density on the limit length of myelin sheath. Panel (a) indicates the effect of sodium ion channels and panel (b) indicates the effect of potassium ion channels (the neuron diameter is set to 5 μm).

Fig. 8. Changes in the nerve conduction velocity (a) and membrane voltage (b) over time at different temperatures.

Fig. 9. The schematic diagram of frog sciatic nerve conduction velocity measuring device.

Fig. 10. Measurement of the nerve conduction velocity in a bullfrog at different temperatures. The red curve is the theoretical calculation result. Panels (a) and (b) show a monotonic rise in temperature. At the time of measurement, panel (c) shows a random temperature change (30 °C → 18 °C → 11 °C → 16 °C → 19 °C → 15 °C → 17 °C →35 °C → 29 °C → 25 °C → 27 °C → 20 °C → 24 °C → 32 °C → 33 °C → 21 °C → 22 °C → 26 °C → 23 °C → 28 °C → 31 °C → 34 °C). Panel (d) shows the measurement results when the temperature decreases monotonically.

Fig. 11. The schematic diagram of effect of temperature on the signal spectrum, the signal has two characteristic frequencies, which are denoted as mode 1 (lower frequency) and mode 2 (higher frequency).

Fig. 12. The effect of temperature on the eigenmode, panel (a) represents the center frequency of the two modes, and panel (b) represents the bandwidth of the two modes, the modes 1 and 2 are represented by blue and red curves, respectively.

Fig. 13. The effect of temperature on the average electromagnetic field energy density at point A in Fig. 2(a) and the signal power (b) (the neuron diameter is 10 μm).

Table 1. Myelin length thresholds that guarantee signal recovery at different temperatures.