The middle and inferior pharyngeal constrictor muscles which are composed of the hyopharyngeal, thyropharyngeal and the cricopharyngeal muscle directly act and convey the bolus from the pharynx to the cervical esophagus. These muscles spread over the midposterior of the thyroid and cricoid cartilage like belts, and act like peristaltic movement of the visceral smooth muscle.
Histochemical and physiological studies were done used the canine cricopharyngeal muscle just after sacrifice.
Histochemical study;
The fresh muscle were frozen and sectioned by cryostat The specimens were then stained by myofibrillar adenosine triphosphatase, phosphorylase, reduced nicotinamide adenine dinucleotid dehydrogenase and succinic dehydrogense. The cricopharyngeal muscle was occupied mainly by the type I fiber, whose occupational ratio was 57%. The type I fiber was recognized at the ratio of 12% in the hyopharyngeal, 20% in the thyropharyngeal, and 16% in the cervical esophageal muscle.
Mechanogram:
The muscle specimen was diluted by the modified Krebs solution aerated by 95% O2. The cricopharyngeal muscle was then electrically stimmulated by 0.5 msec duration rectangular impulse. Time to reach peak tension in single twitch was 380 msec in the cricopharyngeal muscle and 70 msec in the brachial muscle. The cricopharyngeal muscle was easily fused by 10Hz stimmulation, and formed the complete tetanus. The hypoharyngeal and thyropharyngeal muscle didn't show K+-induced contracture, but the cricopharyngeal muscle partially show this contracture while 118 mMol KCI solution was diluted.
Manometric study in man:
A recording catheter with four openings of diaphragmatic transducers 1.5cm apart was swallowed through the nose until the lower esophagus and the recording on swallowing 2ml of water was done with the catheter withdrawn. The sequences of study were done aiming to the pressure change, first, on swallowing at the level of the nasopharynx, oropharynx, hypopharynx and upper most of the esophagus, and secondarily, of dynamic propelling force to convey the bolus ahead in the esophagus. It was an interesting result that there was a physiological low pressure zone around the vallecula of the pharynx. This result reflects the phenomenon that patient complaining of mild dysphagia remains the rest of barium at the vallecula on esophagography. Force to withdow the ball from the esophagus was stronger in male than in female, and at the level of the cricopharyngeal muscle, strain gauge showed the force of 700g in male and 400g in female.
