These parasympathetic neurons make the rectum contract and the internal anal sphincter relax.

这些副交感神经元可以使直肠收缩，并使肛门内括约肌松弛。

Once the rectum is filled and stretched, signals travel to parasympathetic neurons in the spinal cord, initiating the defecation reflex.

当直肠被粪便填满并受到牵拉时，就会向脊髓内的副交感神经元发出信号，启动排便反射。