Wow. I just read a Teisho by Nishijima Roshi mentioning the autonomic nervous system.
I'm reading this document about it:
Yes, I like Roshi's description of Zazen, as Yoga for the spine. I really focused primarily on the mental side of "meditation" before hearing his take on things. Its much more balanced to realize and practice with our bodies just as much as we do our minds. In the end, there is no gap between the two.