You describe a very abstract type of a synapse. Nature is more complex than this. I think it's just a definition problem. What do we mean with modeling a brain? Is it the same like modeling a neuronal network? On which level do we define a brain. E. g. We can also include all chemistry and even fluid dynamics in a cell. E. g. to understand a computer: do we have to have to simulate on the electron leven with doped compounds and barriers, or is it enough to model it with characteristic curves of transistors, or is it even enough to model it on the binary level as switches between 0 and 1?