Which of the following statement(s) is/are true concerning the process of swallowing and esophageal transit of food?

a.Injury to the recurrent laryngeal nerves can cause motility problems of the cervical esophagus and resulting aspiration

c.Relaxation of the LES is mediated via inhibitory neurons

The cricopharyngeus muscle is a continuation of the inferior constrictor of the pharynx and receives its innervation via both the right and left recurrent laryngeal nerves. Although much attention is given to vocal cord dysfunction that accompanies recurrent laryngeal nerve damage, it is clear that cricopharyngeal sphincter dysfunction and motility problems of the cervical esophagus can occur with injury to these nerves. Serious aspiration following recurrent nerve injury is caused not only by the cricopharyngeal dysfunction, but also by additional morbidity incurred because of the inability to close the glottis during swallowing and loss of the protection afforded by effective coughing. Clinically, peristaltic defects of the esophageal body fall into one of to broad categories. One category is characterized by a defect in organization of peristaltic waves, and is primarily a neural phenomenon. The other notable defect is reduction of the power (amplitude) of peristalsis and is usually due to muscle damage secondary to severe reflux or replacement with fibrous tissue as happens in scleroderma and other connective tissue diseases or with severe reflux. The LES provides a pressure barrier between the esophagus and stomach. The sphincter normally remains actively closed to prevent reflux of gastric contents into the esophagus. Relaxation of the LES is mediated by inhibitory neurons. It occurs either to allow entry of food, or to allow exit of air during belching. The ability of the LES to remain closed in the face of a pressure gradient tending to promote reflux of gastric contents from the positive pressure environment of the stomach into the negative pressure environment of the chest depends on several features. The most significant is the resting pressure. However, of equal importance is the ability of the LES to respond to variations in intra-abdominal pressure associated with daily activities. Such elevations would normally be transmitted to the sphincter, causing it to collapse and remain closed, provided sufficient length of the sphincter remains exposed to the abdominal pressure and the compressive effect of the crura. The abdominal length is often reduced in hiatal herniation, because of attenuation of the pharyngoesophageal membrane. The overall length of the LES is also an important determinant of competence, much as the total resistance of a series of resisters in a circuit is the sum of the individual resistances. A mechanically-defective sphincter, however, is not always associated with increased esophageal acid exposure because it may be compensated by the clearance function of the esophageal body. The role of the esophageal body in limiting acid reflux is related to its ability to clear the esophagus of acid. This clearance has two components: volume clearance which requires peristalsis, and chemical clearance which requires saliva.