This plots the VGCC current function, which is an L-type Ca channel that opens as a function of membrane potential. It tends to broaden the effect of action potential spikes in the dendrites.
G(vm) = -vm / (1 - exp(0.0756 * vm))M(vm) = 1 / (1 + exp(-(vm + 37))) // Tau = 3.6 msecH(vm) = 1 / (1 + exp((vm + 41) * 2)) // Tau = 29 msecVGCC(vm) = M^3 H * G(vm)
The intersection of M and H produces a very narrow membrane potential window centered around -40 mV where the gates are both activated, with the fast updating (3.6 msec tau) and cubic dependence on M essentially shutting off the current very quickly when the action potential goes away. The longer H time constant provides a slow adaptation-like dynamic that is sensitive to frequency (more adaptation at higher frequencies).
The Time Run plot (above) shows these dynamics playing out with a sequence of spiking.
Functionally, the narrow voltage window restricts the significance of this channel to the peri-spiking time window, where the Ca++ influx provides a bit of extra sustain on the trailing edge of the spike. More importantly, the Ca++ provides a postsynaptic-only spiking signal for learning.