The oesophagus leads from the back of the mouth, down to the stomach. The oesophagus is about 30 cm long and serves as a passageway, carrying food from the mouth down to the stomach. It does this with smooth, coordinated waves of muscles relaxing and contracting. This process, called peristalsis, happens throughout the whole digestive system. Peristalsis is controlled by special nerve cells, numbering in the billions.

It's however a complicated system, so problems can arise. Problems in the upper digestive system related to poor coordination of these muscular contractions are called motility disorders.