Disorders affecting the motor function of the upper esophageal sphincter; lower esophageal sphincter; the esophagus body, or a combination of these parts. The failure of the sphincters to maintain a tonic pressure may result in gastric reflux of food and acid into the esophagus (gastroesophageal reflux). Other disorders include hypermotility (spastic disorders) and markedly increased amplitude in contraction (nutcracker esophagus).