Why does part of your spine bend and part of it doesn't?

Answer 1

because if you are standing up for a long time your vertebre' kinda settle in then when you bend over it starts stretching that cartilidge stuff in between your vertebre' and it becomes "unsettled" and it makes a cracking noise.

Answer 2

Because your skin is thin and it is going through?

The portion of your spine that is 'showing through' when you bend over is a sharp, triangular bony landmark called the spinous process. There is no muscle sitting over this bony piece, only ligaments thus the skin contours to it almost directly. The skin itself is no thinner in this area than anywhere else on your back.

ANd also because your muscles are stretching

Answer 3

It depends on what is attached to it. Some parts have other bones, like ribs attached. This makes it stiffer and less likely to bend. The same goes with the lower lumbar region which is attached to the pelvis.