Figure 3. Proposed pathways of tocolytic sympathetic and tocodynamic parasympathetic efferents. Nerve transection experiments in pregnant and postpartum dogs suggest that tocolytic sympathetic efferents exit the central nervous system cephalad to T3 and travel to the uterus via the peripheral sympathetic chain. Tocodynamic parasympathetic efferents are interrupted by cutting the pelvic parasympathetic nerves. Epidural analgesia may slow labor by partially blocking pelvic parasympathetic outflow without affecting the tocolytic sympathetic efferents.