Pain pathways. Artwork of a spinal cord section showing pain pathways. Pain is the result of the stimulation of nociceptors (special sensory nerve endings) either by injury or disease. Nociceptors have their cell bodies in the dorsal root ganglia (swelling on the right). There are 2 kinds of pain nerve fibre: fast acute pain fibres & slow chronic pain fibres. Both types connect (synapse) with secondary fibres in the spinal cord. Fast fibres (red) pass impulses to the brain's reticular formation, thalamus & cortex. Slow pain fibres (blue) pass impulses to the reticular formation and thalamus. The purple arrow represents a modifying neuron from the brain.