Spinal nerve roots are the fiber bundles that come off the spinal cord. For each spinal segment, (which is the area of the spinal cord that corresponds to the level of the vertebra through which the nerves will exit on their way out to all parts of the body) there are four nerve roots—two in front and two in back
In front, these roots—a right one and a left one, i.e., one on either side of the spine—contain the nerves that control your body's movement. The nerves and nerve roots in front are called motor neurons.
In back, nerves (again one on the right and one on the left), carry sensory information from the body into the spinal cord or brain and are called sensory neurons. Once it reaches the spinal cord or brain, the sensory information transmitted through sensory neurons is interpreted as feeling.
In all, there are 31 pairs of spinal nerve roots, but after L-1, which is the level of the first lumbar vertebra, the spinal cord ends. This means the nerve roots can't arise from the spinal cord in the same way they do above L-1. Instead, the spinal nerves, contained in and protected by cerebrospinal fluid, dangle down, tapering into a structure called the cauda equina.1 Cauda equina means "horse's tail," which is what this structure resembles to some anatomists.
Nerve Root Compression: Radiculopathy
Some spinal conditions or injuries such as a herniated disc, facet joint hypertrophy and/or spinal stenosis may irritate the nerve root in the back by pressing on it in some way. The symptoms that result, which may include pain, numbness, tingling, electrical shock, burning and/or a feeling of pins and needles going down either one arm or one leg, are called radiculopathy.2
Often confused with sciatica, radiculopathy refers to the symptoms mentioned above that are related to irritation or pressure on a spinal nerve root by a nearby structure that is generally not supposed to be there. Note that radiculopathy is very specific about what causes these symptoms, while sciatica, which refers to this same set of symptoms, can be caused by a number of things that are included but not limited to radiculopathy.
Causes of Compression and Radiculopathy
A herniated disc occurs when the soft inside of the disc (called nucleus pulposus) escapes to the outside by means of a tear or hole in the tough outer fibers that normally contain it.2 Sometimes, the nucleus material "lands" on a nearby spinal nerve root, pressuring it.
In the case of spinal arthritis (to which facet joint hypertrophy and spinal stenosis are related) bone spurs can form over time as a response to wear and tear on the joint and may also cause pressure on the spinal nerve root leading to symptoms of radiculopathy.2
If you have any of these symptoms, see your doctor as soon as you can.