Answer: 6th week of gestation
Explanation:
Anand and Hickey published an article in " THE ENGLANG JOURNAL OF MEDICINE" volume 317, number21: pages 1321-1329, 19 November 1987.
The name of the article was "PAIN AND IT'S EFFECT IN THE HUMNA NEONATE AND FETUS.
In this article they explained pain receptors and when it starts developing in fetus. Their stated that the spread of cutaneous receptors starts by the development of synapses between sensory fibers and interneurons in the dorsal horn of the spinal cord, and this first appears as early as the sixth week of gestation. That means that the first appearance of pain sensation is in the sixth week of gestation, while cutaneous sensory receptors are seen in the perioral area of the human fetus in the 7th week of gestation, which spread to the rest of the palms, of the face, of the hands, and to the soles of the feet by the 11th week.
