Why the spike looks like that
Press Inject with the defaults (10 µA/cm², 1 ms). In the top panel the membrane climbs past rest (−65 mV). Once Na⁺ activation (m) surges in the bottom panel, inward Na⁺ current becomes regenerative: depolarization opens more m, which opens more current — the rising phase. Near the peak, m is high but h is already falling, so Na⁺ conductance collapses even while voltage is still elevated. At the same time n rises more slowly, building outward K⁺ current. The falling phase is therefore h-inactivation plus n-activation working together, not a mysterious timer. After the spike undershoots toward EK because n is still elevated — residual K⁺ conductance — then n relaxes and V returns to rest. Try a 2 µA pulse to see a subthreshold bump with almost no m surge; enable TTX to erase spikes entirely; enable TEA to watch repolarization drag; use paired pulses at 2 ms vs 15 ms and watch whether h has recovered before the second stimulus.
Model note (Squid): classic Hodgkin–Huxley squid giant axon at 6.3 °C. Use Mammalian-like for a faster cortical-style Na⁺/K⁺ rate set — still a single-compartment teaching scaffold, not a morphologically detailed cortical cell.
© Omar Garagozov 2026