In most neuron models the values of maximal conductances of membrane ionic currents are fixed. In our paper we investigate spiking activity of the neuron model activated tonically by NMDA synapse, when the membrane ionic currents are dynamically dependent on calcium concentration, as in a model by Abbott and coauthors (1993). A spiking neuron model (in Matlab/Simulink environment) is based on the properties of lamprey spinal neurons. The basic neuron is a one-compartment model with voltage-gated Na+, K+, Ca2+, KCa+ channels. The Na+ and K+ currents are described with the dynamic equations of Hodkin-Huxley model (Hodgkin and Huxley 1952). The Ca2+ and KCa+ channels are modeled using description of calcium dynamic introduced by Ekeberg and coauthors (1991). The model was tonically activated by NMDA synapse, described by a kinetic model of synaptic transmission. We analyzed the activity of this model and showed that when only one of conductances is calcium-dependent, the cell is not able to react to and recover from external perturbations.