![]() The motoneurons of the CP are found in the nucleus ambiguus, and the innervation is ipsilateral for animal species in which the CP has a median raphe. Parasympathetic ganglia and various peptides (galanin, cGRP, VIP, neuropeptide Y, substance P, tyrosine hydroxylase) have been found in the CP, but their role in control of the CP is unknown. The GLN may be sensory the sympathetics may innervate the mucosa, blood vessels, and glands but no functional innervation by the RLN has been identified. Only the PE and SLN provide motor fibers to the CP. The CP is innervated by branches of the vagus nerves: pharyngoesophageal (PE), superior laryngeal (SLN), and recurrent laryngeal (RLN) glossopharyngeal (GPN) and cervical sympathetics. The high compliance of the CP allows it to be opened by distraction of other muscles (e.g., geniohyoideus) or increased intraluminal pressure. ![]() A passive tone in the CP is present and increases through all degrees of stretch. The optimum length of the CP for development of active tension is about 1.7 times resting length therefore, in some respects the CP acts more like cardiac than striated muscle. In humans and rats, but not other animals, the CP has no median raphe. The fibers may attach to the connective tissue framework, forming a muscular net. The CP is a striated muscle composed of variable-sized small (25-35 microm) muscle fibers that are primarily type I (slow twitch), highly oxidative, and contain abundant (40%) endomysial elastic connective tissue. All 3 muscles may at times function to maintain tone in the UES, but only the CP contracts and relaxes in all physiologic states consistent with the UES. The entire sequence of events is studied using high resolution solid state manometry.The upper esophageal sphincter (UES) is composed of the cricopharyngeus (CP), thyropharyngeus (TP inferior pharyngeal constrictor in humans), and cranial cervical esophagus. Routine high resolution solid state manometry is a standard routine technique is currently performed in awake patients sitting upright voluntarily requested to swallow small boluses of liquid. Thus patients can't protect their airway by maintaining competence and appropriate relaxation of the upper esophageal sphincter. During the early period of emergence from anesthesia, the aspiration risk is highest due to the sluggish return of the resting pressure in the upper esophagus and the lack of normal coordination with involuntary swallowing. The above is the normal sequence in humans, a process which maintains absolute separation of the airway and digestive passageways despite being in intimate proximity. Peristalsis then begins in the body of the esophagus leading contents to the stomach. The swallowing sequence in normal awake persons begins with 1) the contraction of the upper and middle pharyngeal constrictors, 2) the posterior movement of the tongue and 3) the prompt relaxation of the contracted upper esophageal sphincter. ![]() In normal awake individuals the upper esophageal sphincter (also known as the cricopharyngeus or the inferior pharyngeal constrictor) is contracted and relaxes precisely timed with voluntary or involuntary swallowing. Patients cannot reliably maintain competence of the upper esophageal sphincter, thus aspiration of the contents from the mouth or regurgitated material from the stomach can be aspirated into the lungs leading to serious complications. The emergence from routine general deep anesthesia with an endotracheal tube is a potentially dangerous time for patients.
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