Figure 1 - Esophagus: anatomic considerations.

Note that the cervical esophagus and the small part of the thoracic esophagus that includes the upper esophageal sphincter are composed of striated muscle. The lower two thirds of the esophagus, including the thoracic and abdominal parts containing the lower esophageal sphincter, are composed of smooth muscles. The diseases of the striated muscle include polymyositis and myasthenia gravis, whereas scleroderma and achalasia are diseases that involve the smooth muscle portion of the esophagus. (Source: AGA Gastroenterology Teaching Project, 2001, 2^nd Ed. Unit 9, Esophageal Disorders, Slide 12, used with permission. Copyright © American Gastroenterological Association, Bethesda, MD)