To nitpick, it is not as grand as mind-over-matter, but rather conscious control of things that are normally under the control of the sympathetic or parasympath

To nitpick, it is not as grand as mind-over-matter, but rather conscious control of things that are normally under the control of the sympathetic or parasympathetic system. IIRC the sympathetic system is more likely to be consciously influenced. Both are vital subsystems that control things like heart rate, blood pressure, etc. that you'd rather not play too much with (although it is said that you can with deep meditation). Your question are about different things than that, and the first one is about a different thing than the second one. Learning to move a particular muscle you don't normally use consciously (like moving your ears or your nostrils) is indeed a matter of practice. Sometimes all it takes is getting conscious that there is a muscle there, and then you improve your feedback loop between sending a command and feeling it move. But a muscle that uncontrollably twitches is a whole different process. For instance some muscle cramps are related to dehydration or lack of certain minerals. So the cause can be more chemical than nervous system (ie coming from the nervous system). PS: I have no particular expertise in this area.