If you get pins and needles, pain, weakness or feelings of electrical shock down your arm or leg (sciatica), chances are you have a syndrome known as radiculopathy. There are a number of causes of radiculopathy, but usually a herniated disc is responsible. Symptoms of radiculopathy indicate that a spinal nerve root is pinched, pressured or otherwise cajoled. In other words, those pins and needles and other things you feel in your arm or leg are there because you have nerve involvement.
With radiculopathy, it's like the pain and other symptoms are assigned specific zones to be in. This is because at each level of your spine (called a segment), nerves exit the spinal cord (from holes called the intervertebral foramen) and branch out to wire the rest of your body for feeling and movement. The useful thing about the zones is that the can be tested for abnormal feeling or function,and your doctor can narrow down the area she thinks the pain is coming from.