Nerve Injury and Pain

Nerve injury and pain is an extraordinarily complex topic and a full discussion of it is beyond the scope of this website; however the nerves of the arm may be injured by excessive compression forces, traction and repeated 'friction' movement of the nerve 'rubbing' against a muscle, fascial sheet or bone. 
Following injury or irritation, pain may arise from the axon (copper wire) or from the insulation layer; or from both. Pain may arise from the nerve without there being any loss of message conduction in which case nerve conduction studies would most likely be normal. The pain may arise from as few as 30 axons out of the thousand or so axons in the nerve. The changes in the nerve structure causing the pain are on a microscopic level and therefore do not show up on ultrasound or Computerised Axial Tomography (CAT) scans or Magnetic Resonance Imaging (MRI)

swellling a the soup

A very good and much more complete description of nerve related pain and persistent pain can be found in the book 'Explain Pain' by David Butler and Lorimer Moseley (NOI Publications).