What event triggers the opening of the gastroesophageal sphincter?

Peristalsis in the Esophagus event triggers the opening of the gastroesophageal sphincter.

Explanation:

In the esophagus, there are two types of peristalsis occurs.The first one is a "primary peristaltic wave" occurs through which bolus enters esophagus during swallowing. This "wave pushes the bolus down esophagus", into stomach in a wave lasting about 8–9 seconds.The esophageal sphincter in the lower region is separated by both sympathetic and parasymphathetic nerves. The pathways of vagal are a major for the relaxation of reflex of LES and this occurs in LES relaxations.