Pain pathways, computer artwork. The heat of the candle is detected by nociceptors (special sensory nerve endings) in the finger. The pain impulse is passed via the peripheral nervous system to the spinal cord (bottom right) where the nerve synapses with neurons (nerve cells) in the dorsal horn of the grey matter. The signal is then sent up the spinal cord, through the white matter, to the brain stem and synapses with neurons in the medulla (white triangle at base of brain) and the thalamus (white ovals at base of brain). From these points the signal is spread to other parts of the brain. The blue arrow represents a modifying neuron from the brain, which provides pain relief.