Figure 1.
Action potentials recorded in neurons in rat neocortex (A1–C1 and A2–C2) and in snail neuron (A3–C3) have different onset dynamics.
A: Waveform of the action potentials recorded in two rat neocortical neurons at 34°C (A1) or 24°C (A2) and in a small cerebral neuron (20 µm soma diameter) in snail (A3). B: Phase plot representation of the APs from A. C: Close-up of the initial portion of the phase plots indicated with boxes in B. Magenta lines show exponential fits, Cyan lines piecewise linear fits to the data. Ratio of errors of exponential fit over the piecewise-linear fit were 8.22 in C1, 12.3 in C2 and 0.55 in C3. Note different onset dynamics of the APs: rapid, step-like in rat neurons, but slow, exponential-like in the snail neuron.
Figure 2.
Population analysis: Ratio of the errors of exponential fit over the piecewise-linear fit for rat and snail neurons.
A: Distributions of the ratio of errors of the exponential fit and piecewise-linear fit of the initial part of APs for 49 rat neocortical neurons and 29 snail neurons. B: Scatter plot of the error of exponential fit against the error of the piecewise linear fit for the neurons from A. Notice double-logarithmic scale. Each point represents data for one neuron. Colour code is the same in A,B.
Figure 3.
Action potentials in either rat and snail neurons have different waveforms.
A, B: Action potentials recorded in 4 different neurons from rat neocortex. In A, voltage traces (V) are shown together with their first (V') and second (V”) derivatives. In B, phase plots of action potentials from A are shown. Ratio of errors of exponential fit over the piecewise-linear fit for these neurons were: 7.27; 6.07; 6.95; 3.46. C, D: Action potentials recorded in 4 identified snail neurons and their phase plots. Recordings from visceral ganglion neuron Visc5 (C1,D1); Left pedal ganglion neuron LPd2 (C2,D2); Right cerebral serotonergic neuron RC5HT (C3,D3) and Left pedal ganglion neuron LPd7 (C4,D4). Notice 8-fold difference in the Y-scale between B and D. In A–D open arrows indicate double-peak on the second derivative trace and bimodal shape of the phase plots. For both rat and snail neurons, the APs are sorted from left to the right by the increasing strength of manifestation of the double-peak on the second derivative trace and bimodal shape of the phase plots (open arrows). Ratio of errors of exponential fit over the piecewise-linear fit for 1–4 were: 0.79; 0.70; 0.92; 3.14. Notice that all APs in rat neocortex neurons have a sharp onset, irrespective of the presence and expression of the double peak in the phase plots.