The brain has no central processor. There is no great decision making unit. There are many specialized processors which work in series and in parallel. Though no element can control their particles, the system can control its elements and that's where free will comes from.

How do you explain this conversation that we're having? How do you see no free will in what we're doing? If I choose to speak, I impact the universe of particles which then move in a predictable way, but I do not speak in a predictable manner.