This writup on the Physiology of pain appears to be very well written.
Of note is the paragraph under the heading of A-Delta and C-fibers in the Physiology of Pain.
A-delta fibres are thinly myelinated and have conduction speeds of 5-15 metres per second. These ‘fast’ pain nerves signal the initial pain as a result of trauma. I believe it is these nerves that are the result of HNPP primary pain. Stabbing, shock-like pain.
Another very good article on the Anatomy and Physiology of Pain can be found at the Nursing Times, UK.