Animals sense painful stimuli through specialized sensory neurons on the skin and generate nocifensive behaviours to protect themselves from severe injury. Specialized sensory neurons carry nociceptive information to the central nervous systems (CNS) locates in the spinal cord dorsal horn to trigger avoidance behaviour. Recently, our lab identified a distinct class of sensory neurons (called Smr2+ neurons due to the unique expression of the gene Smr2) whose activation triggers nocifensive behaviour in mouse (unpublished data). We propose combining the X-ray phase contrast nanoscale tomography with electron microscopy to fully reconstruct the local neural circuitry involving Smr2+ sensory neurons in the spinal cord. Identifying the CNS neurons that process nociceptive information from Smr2+ neurons will represent a major step toward understanding how pain is sensed and processed by the nervous system.