The body-systems have an overall (manager) controller, centered in the belly area (although it has most of its own structures a few meters lower than that in its own space), which controls various functions of the body.
This controller is in some ways the owner of the physical-body, and has communication-links to most other body-systems. There are also sub-controllers for each part of the meat and bones-body, including all organs and smaller structures and conceptual areas etc. as well as other controllers outside and below the body. Each of the body-controllers has internal structures which do things including defining the condition of the relevant part.
The main controller desires to rise up to being an Ultimate-self, and can be converted to a Ultimate-self by giving it a strong connection to Ori (Higher-self), typically at around the time of the death of the body that it is currently controlling (some Tibetans do this regularly) although it can be done at any time in which case a new Body-controller forms in its place. A normal death will free the Body-controller so it will partially re-merge with the commonality of Body-controllers for that species, and some time later, find a new body to join.
On human bodies owner by an Ultimate-self, there is usually a false Body-controller, which is an additional Ultimate-self in too low condition to own a body itself. Ideally this should be improved up to being able to go through the Between-lives sequence and own a body of its own.