The activity of the above parts is periodic, periods of relaxation preceding periods of contraction. The esophagus resumes activity before the stomach. Sudden distention of the lower end of the gullet causes it to undergo peristalsis, whereas the stomach simultaneously relaxes. These functional interrelations are considered purposive, resulting in propelling a bolus of food from the esophagus into the stomach. They are dependent on the intact state of the vagus nerves.