Abstract
The cricopharyngeal muscle which has been called a sphincteric muscle maintains a sustained contraction, except during deglutition. This fact is apparent from manometric, radiographic and electromyographic studies. To elucidate the functional specificity of this muscle, investigations are made on the relationship between the histochemical structure and the function of the canine swallowing muscles in the inlet of the esophagus (hyopharyngeal, thyropharyngeal, cricopharyngeal and upper esophageal muscles).
Enzymes of muscles, namely myofibrillar adenosine triphophatase, phosphorylase, reduced nicotinamide adenine dinucleotide dehydrogenase and succinic dehydrogenase were histochemically stained. From the above procedures, the canine swallowing muscle fibers could be divided into two types. The type I muscle fiber showed low activity with myofibrillar adenosine triphosphatase (pH 9.4) and phosphorylase, and high activity with reduced nicotinamide adenine dinucleotide dehydrogenase and succinic dehydrogenase. On the other hand, the type II muscle fiber showed high activity with myofibrillar adenosine triphosphatase (pH 9.4) and phosphorylase, and low activity with reduced nicotinamide adenine dinucleotide dehydrogenase and succinic dehydrogenase.
The ratios of type I muscle fibers contributing in the hyopharyngeal, thyropharyngeal, cricopharyngeal and upper esophageal muscles are 12%, 20%, 57% and 16%, respectively. Since the cricopharyngeal muscle is mostly composed of type I muscle fibers, it is assumed that the type I muscle fibers play an important role as the sphincter in the cricopharyngeal muscle.
