A homunculus is the visible representation of what the brain pays most attention to in regards to different aspects of the human organism. For example, there will be plenty of attention to the feet, hands and genitalia. To the brain, the spine is one entity and a small one. As someone that went to school to study the spine for a living, this was a surprise to me.
I first heard this in one of the Functional Range Release seminars. (I highly recommend) In fact Dr. Andreo Spina just wrote an excellent article actually covering this topic and his thoughts on the deep structure of the body. Function of Anatomy: The Spine.
The reason I'm writing these thoughts down now is that reading that article reminded me of some of the things I'm doing with patients or I should say at least checking lately. If the brain truly thinks of the spine as "one thing" then if there is lack of support on the left lower back, perhaps the left neck muscles will also get involved to try to help. Because, to the brain, anything left of the spine may help.
Going through some of Charlie Weingroffs information from "Lateralizations and Regressions" DVD (I highly recommend) he talks about the quadratus lumborum and the scalenes being the same. The SCM and Obliques are the same. I've heard that the deep neck flexors, longus coli/capitus are the psoas of the neck. When we start to view the spine as one thing, these muscular patterns start to make sense.
So next time you are treating someones Scalenes or SCM, think perhaps there are other muscles that the brain is having work to stabilize the spine.