1. Pain is 100% of the time, an output from the brain. In 1996, Ronald Malzack developed the concept of the neuromatrix. The neuromatrix, in simplistic terms, is all of the mechanisms within the brain, that when activated, produce pain. So when your ankle hurts, the pain is generated by information gathered by the brain. Pain is simply a defense mechanism developed to protect the body.
2. The degree of injury does not always equal the degree of pain. Research has told us that very major injuries may not hurt at all and very minor injuries may hurt alot. The degree of pain you experience is more related to past experiences. For example, if you have sprained your ankle in the past and then you sprained it again, the second sprain will likely hurt more. This is because the brain has learned to protect that ankle following the prior injury and defends it through pain.