Hmm. If we understand that "the nervous system" includes our responses to everything from a hot stove to profound trauma, could this be the reason our back "goes out" during times of emotional stress? I think so.
So how can we take care of this vital part of our anatomy? What follows is by no means an expert description of spinal mechanics, but hopefully it will be a start.  Normally the spine can move in the following ways:
bending forward (flexion) bending backward (extension) bending to each side (lateral flexion) twisting (rotation). Protected inside the bony skull and spine are the brain and spinal cord. They float in the spinal fluid, which brings in oxygen and nutrients and carries away wastes. (It's actually the "cerebrospinal fluid" because it is manufactured in the cavities of the brain, but that's kinda long so people usually say "spinal fluid.") Unlike the heart, which pumps blood through the body, there is no circulation system for the spinal fluid. That means it won't move on it's own, so we must facilitate its flow with appropriate exercise of the back. You wouldn't want the oil in your car to sit there instead of working its way through the engine, right? Besides bending and twisting, the breath also circulates spinal fluid through gentle movement of the skull bones. (Another not-so-subtle pitch for breathing brought to you by Yoga Bits!) Injury or atrophy can inhibit movement of the spine. Not moving very much (or at all) can be addressed by deepening the breath and gradually increasing activity. Injury is another matter entirely. Resuming activity after serious injury is a process specific to each situation and must be handled carefully. However, injury is not always immediately apparent. For that reason, listening to your body is extremely important both on and off the mat. If you don't listen, you can cause the kind of harm that won't show up right away but will announce itself 20 years later when you, say, pick up a basket of laundry or a grandkid. To defend against invisible injury while on your yoga mat, it's wise to listen to physical cues. For example, if you are twisting during yoga class and you feel a twinge or you have to pull on another part of your body (usually a knee) to take the twist further, just back off. You will still get all the vital benefits of twisting -- detoxification, moving the spine, improving digestion, releasing hips and shoulders, etc. -- without hurting yourself. Off the mat, spinal health has more to do with general self-care. This includes getting enough rest. Lack of rest causes serious problems for the spine, especially the intervertebral discs. The discs are like spongy little cushions between the vertebrae. All day long your discs take a pounding, getting smushed and flattened while you walk through the grocery store or sit at your desk. That's okay, though, because the body in all its wisdom has a built-in method of repair. During sleep, the discs puff back up by refilling with (guess what) spinal fluid to prepare for another day of smushing. If you don't get enough sleep, you're not giving your spine a chance to rebound. Over time that could cause major problems. So give your spine a break...no, wait, poor choice of words. Just take good care of with a bit more awareness and effort. | 
As I sit here crouched over my computer typing out Yoga Bits, I'm thinking about my yoga anatomy teacher, 