We present a new model of smooth muscle that can be used to simulate the effect of Functional Electrical Stimulation (FES). It is composed of a set of differential equations based on the physiological reality so that parameter's values are meaningful and can be used for quantitative and objective evaluation of the muscle state. Moreover, the model has an input controlled by an FES signal so that it can simulate the behavior of the muscle under artificial stimulation. We apply this model to the simulation of the bladder contraction through the detrusor stimulation. It shows that the model is able to predict the time response, the intravesical pressure and the necessary time to empty the bladder. Simulations show consistent data with the literature. These preliminary results, after in vivo validations, will be used to caracterise bladders that need to be stimulated, for instance for paraplegics, and then to optimize the needed stimulation when neuroprosthesis are used to restore the emptying function.