I believe that the human being, a complex whole of several systems of organisms, has two different sets of reactions. The first one being the internal; blood cells multiplying, stomach digesting food, lungs breathing etc. and the second the external; an intricate and very intimate relation between our sensory system and our plethora of chemical formations.
We have a very limited, if not no, control over the first one. It’s functions are fundemental to our survival. For example, our internal body is dependent on nutrition, food and water. It is absolutely essential that we eat and drink. Again, our blood cells multiplying and our lungs expanding in out to get oxygen are some other actions that are out of our control.
The second somewhat external reaction can be explained as the heathrow of ideas, influences from the outside world and the chemical elements of our internal part reacting to the external. Sense and sentual experiences play a key role in this complex reaction as they help us to understand in the literal sense and as they set the adequate tone for the particular reaction.
To cut it short, I think free-will doesn’t exist for the first one and does exist to a certain extent for the second one.