This paper presents the design and electrical characterization of a SPICE model emulating the neuron membrane electrochemical behavior. This constitutes a tool that predicts action potential time-domain evolution, identifying the minimum input charge/second threshold inducing neuron electrical firing. The cell membrane ionic channels are described by custom components in Verilog-A. By stimulating the model, it is possible to obtain action potentials consistent with the mathematical model based on Hodgkin-Huxley equations. The neuron circuit was validated by extensive transient simulations in Cadence. This tool allows the integration and simulation of the biological environment in Electronic Design Automation (EDA) software.