What is the dip below rest after a spike called, and why does it deepen during a train? · Lobeworks/17
The afterhyperpolarisation, or AHP.
What is the dip below rest after a spike called, and why does it deepen during a train?
The afterhyperpolarisation, or AHP. Potassium currents that outlast the spike pull the voltage towards EKE_KEK, around −90 mV, through IK=gK(V−EK)I_K = g_K(V - E_K)IK=gK(V−EK). Some of them are opened by the calcium each spike lets in, gKCa=gˉKCa s([Ca2+])g_{K_{Ca}} = \bar g_{K_{Ca}},s([\text{Ca}^{2+}])gKCa=gˉKCas([Ca2+]), so the more spikes in a row, the more calcium, the more open channels and the deeper the dip: when the next spike comes before the last dip has faded, the two add up.