I have a bunch of papers on the contributions of a stabilized platform (the vestibular system) as the starting point of self-reference - but you may wish to start with this one.

What happens if it is broken?

This is closely related to Depersonalization:

Update: I did a little digging and ran across this text. Considering the question you are asking about the system organization of the motor system I think you will be interested in the diagram on page 222 of this book. Sorry - not open source; perhaps available from the library?