Circuit of the pain of the muscles, joints, viscera in the brain .. Rise of the nerve impulses painful of the cutaneous, muscular, artucular or visceral tissues since the nociceptors, in yellow until the spinal cord, then in red until the cortex brain through the medulla oblongata and the mesencephalon of the brain stem seen in horizontal sections. Inibition by descending routes in pink. zoom on the enkephalin neuron of the spinal cord in blue and the opiate receptors on the yellow neuron