Nerve roots are the fiber bundles that come off the spinal cord. For each spinal segment, there are four nerve roots - two in front and two in back. In front, ventral nerve roots contain the nerves that control your body's movement (called motor neurons). In back, nerves in the dorsal nerve roots carry sensory information from the body into the spinal cord or brain. Once it reaches the spinal cord or brain, the sensory information is interpreted as feeling.
The nerve roots, like the spinal cord, are located inside the spinal canal. Some spinal conditions or injuries such as a herniated disc may irritate the nerve root in the back by pressing on it. This may cause pain, weakness, pins and needles or numbing down your leg (sciatica) or arm. If you have any of these symptoms, see your doctor as soon as you can.