The Jacobi process is a stochastic diffusion characterized by a linear drift and a special form of multiplicative noise which keeps the process confined between two boundaries. One example of such a process can be obtained as the diffusion limit of the Stein?s model of membrane depolarization which includes both, excitatory and inhibitory reversal potentials. The reversal potentials create the two boundaries between which the process is confined. Solving the first-passage-time problem for the Jacobi process, we found closed-form expressions for mean, variance and third moment, that are easy to implement numerically. The first two moments are used here to determine the role played by the parameters of the neuronal model. Namely, the effect of multiplicative noise on the output of the Jacobi neuronal model with input- dependent parameters is examined in detail and compared with the properties of the generic Jabobi diffusion. It appears that the dependence of the model parameters on the rate of inhibition turns out to be of primary importance to observe a change in the slope of the response curves. This dependence also affects the variability of the output as reflected by the coefficient of variation. It often takes values larger than one and it is not always a monotonic function in dependency on the rate of excitation.