In part 6, having normal spinal joint motion stimulates the parasympathetic nerves to allow the adrenal glands to release relaxation hormones (adrenaline, serotonin) to keep the body relaxed (your muscles, brain, organs, etc.). This leads your body to recharge when you sleep, giving you more energy, keeping you healthy.
That’s it!!!
To understand this body’s response to limited spinal motion, here are the links to the full video and part 1-4: