How does the spine form?

The human spine is shown here in rear and side views.
The human spine is shown here in rear and side views.

In a way, your spine is the keystone that holds your body together. It's at the center of your axial skeleton -- the flexible column that holds up the center of your body. At the top of your axial skeleton is your skull, and your coccyx, or tailbone, is at the other end. Together, all these bones shelter some of the most important organs in your body. Your brain sits in its protective skull casing, and the organs in your chest are protected by 12 pairs of ribs, all of which attach directly to your spine.

As if that wasn't enough, your spine is also what lets you move your arms and legs. Your arms attach to your spine and ribs via the collarbones and shoulder blades. Your legs attach to the spine through your hips. When you want to move your arms and legs, signals travel down your spinal cord, which is enclosed in your spine. Nerves carry the signals from the spinal cord to the muscles you want to move.

Arms and legs aren't the only parts of your body that move around, though -- your axial skeleton is also flexible. Discs provide lubrication between each of the 26 bones in your spine. As long as your discs are healthy, your vertebrae don't grind together when you bend and twist. Muscles attach to protrusions on the vertebrae called processes. When the muscles contract, they pull on these leverlike surfaces, and your vertebrae move.

Since your spine has a lot of responsibility, it's not surprising that it has to develop in exactly the right way in order for the whole system to work. So where does it come from, and what can go wrong as it grows?