Muscle anatomy of the human esophagus.

We studied the esophageal musculature of 11 cadavers to assess the distribution of striated and smooth muscle. The lower 54-62% of the esophagus was found to be exclusively smooth muscle, the proximal 4.1-5.6% to be exclusively striated, and the remainder to be mixed. The area in which striated and smooth muscle portions were approximately equal, the 50/50 point, was found to be 4.7 +/- 0.6 cm from the proximal portion of the cricopharyngeus muscle. This point corresponds to the previously described physiologic low pressure zone in the proximal esophagus.