COMMENT calcium accumulation into a volume of area*depth next to the membrane with a decay (time constant tau) to resting level given by the global calcium variable cai0_ca_ion ENDCOMMENT NEURON { SUFFIX cacum USEION ca READ ica WRITE cai RANGE depth, tau, cai0 } UNITS { (mM) = (milli/liter) (mA) = (milliamp) F = (faraday) (coulombs) } PARAMETER { depth = 1 (nm) : assume volume = area*depth tau = 10 (ms) cai0 = 50e-6 (mM) : Requires explicit use in INITIAL : block for it to take precedence over cai0_ca_ion : Do not forget to initialize in hoc if different : from this default. } ASSIGNED { ica (mA/cm2) } STATE { cai (mM) } INITIAL { cai = cai0 } BREAKPOINT { SOLVE integrate METHOD derivimplicit } DERIVATIVE integrate { cai' = -ica/depth/F/2 * (1e7) + (cai0 - cai)/tau }