"Pain can be detected when nociceptors (pain receptors) discharge electrical impulses to the spinal cord and brain. These fire impulses outward, telling the muscles and body to react. These can be measured. Mountcastle, Medical Physiology, St. Louis: C.V. Mosby, pp. 391-427 "Lip tactile response may be evoked by the end of the 7th week. At 11 weeks, the face and all parts of the upper and lower extremities are sensitive to touch. By 13 1/2 to 14 weeks, the entire body surface, except for the back and the top of the head, are sensitive to pain." S. Reinis & J. Goldman, The Development of the Brain C. Thomas Pub., 1980"