"Before any information about a noxious or tissue damaging stimulus can reach the brain, it has to be transmitted through the spinal cord (for the body) or the brainstem (for the head and neck). This transmission requires the growth of nerve fibres from the skin to the spinal cord or brainstem and then further growth of nerve fibres along the spinal cord or brainstem and into the brain. Staining of postmortem tissue reveals that nerve fibres grow into the fetal spinal cord from 8 weeks. These fibres, however, are specialised for the control of movement and some aspects of touching or prodding the body or positioning a limb. The growth of nerve fibres connecting nociceptive terminals to the spinal cord lags behind that of other sensory inputs in non-human mammals. Similar connections in the human are also likely to lag but the specific timings remain unknown. Preliminary studies have failed to demonstrate nerve fibres from nociceptive terminals in the fetal post-mortem spinal cord before 19 weeks."