Answer:
This is in a realm of true and in a realm false, but you experience me as you turn and toss.
I am mother and father, but never birth or nurse. I'm rarely still, but I never wander.
I open wide and tight I shut, Sharp am I and paper-cut fingers too, so do take care, I'm good and bad, so best beware.
Only two backbones and thousands of ribs.
Reaching stiffly for the sky, I bare my fingers when its cold. In warmth I wear an emerald glove and in between I dress in gold.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?