Involuntary responses are not under your control and are not "determined by physical processes in your brain", but are considered actions. Voluntary responses are also influenced by factors occurring outside your brain. If you're tired, you are not likely to do any heavy exercise although you are able to choose to do so. If you see an explosion in front of you, you are likely to drop to the ground or run away.

I see now (after reading yours and janos' comments), that my definition isn't perfect; but I think if you exclude some brain parts and include some other systems, my argument against seeing IQ as external will still hold (at least if your definition still includes brain parts which affect IQ).

Yes, internal locus of control factors such as clothing, diet, or hair style are a major influence on attractiveness, but height; I have never heard anyone make that argument before. How is height under my control or what sort of arguments could be made in favor of such a belief? I recognize you are not actually arguing this is the case, but I'm not sure how you could even consider this to be a plausible argument.

I'm not arguing that height is under your control; that would be strange indeed. But the physical factors are sometimes considered properties of a person, so I included things as height as an example of what considered "internal factor". I tried to analyse the locus control question in the most general case, that is, define two categories, "internal" and "external" (whatever that actually means), and then find out which is the most important. Basically, I argued that you can't have IQ in one category and brain in the other.