Final answer:
In the second stage of labor, pain is primarily transmitted through the Sacral (S1-S5) dermatomes. The baby is expelled from the uterus and descends through the birth canal.
Step-by-step explanation:
The second stage of labor, during the passage of the baby through the birth canal, primarily transmits pain through the Sacral (S1-S5) dermatomes. In this stage, the baby is expelled from the uterus and descends through the cervix and vagina. The mother typically pushes during contractions to aid the delivery.