Couple Ideas
So I just wanted to clear a few things up.
The meridians in the body of all living creatures are physical and exist throughout the body similar to the circulatory system. The meridians help keep the body alive using mana, sometimes this mana is in excess resulting in stronger physiques or natural regeneration.
The soul is weird right? The soul isn't physical in most others books but I wanted to make some sense with soul cultivation. So the core of the soul is actually physical. Think of a slim okay they are portrayed as having a core with a gelatinous membrane protecting the core. That is where the inspiration came from.
Combing this though the soul core resides within the center of the brain where multiple meridians can connect. It's why a cultivator could be killed if there head is destroyed, otherwise it would just regenerate. Furthermore if a cultivators head is destroyed but not the soul core and at least one meridian then the head can regenerate.
I know it's quite weird and all that but I felt that these where some interesting ideas.