There is only one substance that is connected continuously throughtout your body - the fascia. Bones start and stop. So do muscles, tendons, ligaments, organs... The only thing
that is in continuous connection in your body is the fascia.
If you have ever removed the skin from a chicken, you will recognize the kind of sticky stringy stuff that connects the skin to the meat. That is fascia. If creates little compartments in your body so that things don't get tangled up. It also provides the structure of the flesh.
When you hold a posture for a long time the fascia grows into that shape. When you try to correct your posture, as soon as you stop trying to hold the new shape, the fascia pulls you into the old shape. So you have to stretch out the fascia by either exercise or massage before you can fix the problem. Then you must hold the correct posture, by adjusting to it every time you think of it, for 4 to 8 weeks until new fascia grows into the new shape. (Think of a broken bone knitting. ) Then the new posture will be automatic.
I recommend making changes like this under the supervision of an experienced body worker of some sort be it a doctor, massage therapist, tai chi or yoga teacher, etc. With the fascia everything links to everything else. You want to make sure the changes you make don't cause problems somewhere else.