There are some theories that are available to explain clinical aspects of pain, but none explain all aspects.
Proposes that there are specific pain receptors (free nerve endings) located in periphery and go to a specific pain centre in brain. Impulses transmitted along A-delta and C fibres.
Pain is result of intense stimulation of nonspecific receptors travels along nonspecific pathways to brain
However, there is evidence of receptor specific fibre specialisation
Central summation theory:
Reverberating circuits in spinal interneurons result from intense pathological stimulation – they can be activated by normally non-noxious stimuli abnormal amounts of impulses interpreted as pain