The nerve roots exit the spine from each side at every spinal level.  They make up the nerves of your body and carry signals from your skin and to the muscles.   When one of these nerves is irritated by a disc herniation or pinched on by bone or a disc bulge, it can cause numbness, tingling, and sometimes weakness down an arm or a leg.  The nerve roots can also be bruised and pinched by a sudden closing of the intervertebral foramen without any obvious signs of ipmingement (see anatomy lession, note the nerve root coming out from the arm pit of the dog).

The nerve roots have names like C5, L5, and S1.  The letter, (like "C" in C5) stands for the spinal area, in this case, cervical.  The number after the letter (i.e. "5" in C5) is the exact nerve root in that area.  Sometimes, when the nerve root is being pinched badly, surgery needs to be performed to free it up.