Final answer:
The vagus nerve, a part of the parasympathetic nervous system, directly controls the digestive system by sending signals to activate digestive function through the enteric nervous system.
Step-by-step explanation:
The vagus nerve is part of the parasympathetic nervous system, which directly controls the digestive system. It sends signals to activate digestive function through the enteric nervous system. The nucleus ambiguus and the dorsal motor nucleus of the vagus nerve are important brain stem nuclei that contribute to the parasympathetic output of the vagus nerve and regulate functions such as relaxing bronchial tubes in the lungs and decreasing heart rate.