There are no such things as pain nerves. We have a number of types of nerve fibres in our bodies, but none of them actually conveys the sensation of pain. IF you think pain is as simple as a hard-wired system where something nasty happens in our body and our brain immediately and always registers pain, then you need to re-visit the clip on the relationship between pain and damage. We have nerve fibres in our bodies which detect noxious events – they are called nociceptors. They may respond to severe temperature changes, trauma, inflammation, sudden and/or large stretching of tissues – remember bending your finger back. They respond to these events by sending an electrical impulse to the spinal cord. They may keep firing for a while after the noxious event, and will continue to fire in the presence of inflammation, which sensitises them.
All sensations –vision, hearing, touch, smell, pain – require the brain to interpret information coming into it and then to create those sensations and project them back to where they came from. We feel as though we see with our eyes, hear with our ears and smell with our noses, but without the related parts of the brain those sensations would never be experienced. The same is true for pain – you may feel it in your back, but without your brain to interpret the information coming into it, you wouldn’t feel that pain at all.