![]() PreTest Self-Assessment and Review Fifth Edition This recommendation is of particular importance in connection with new or infrequently used drugs. For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this work is accurate and that changes have not been made in the recommended dose or in the contraindications for administration. Readers are encouraged to confirm the information contained herein with other sources. However, in view of the possibility of human error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the results obtained from use of the information contained in this work. The authors and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication. As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required. Notice Medicine is an ever-changing science. A focal weakness or deficiency in this area of the pharyngeal wall is termed a Killian dehiscence and can produce a pulsion-pseudodiverticulum, known as a pharyngeal diverticulum or pouch (Zenker diverticulum).Clinical Vignettes for the USMLE Step 2 CK TM The area of the pharyngeal wall at the junction between the thyropharyngeus and the cricopharyngeus is a potentially weak area. The middle and superior constrictors are enclosed by the thyropharyngeus fibers that wrap around to the midline raphe.The recurrent laryngeal nerve and inferior laryngeal vessels pass upwards deep to the lower border of the cricopharyngeus.It is always closed except for momentary relaxation during swallowing. Its closure prevents air from being sucked into the upper esophagus when intrathoracic pressure falls, allowing air to be sucked only into the permanently open trachea. It is physiologically in a tonic state, constricting the distal end of the pharynx (in coordination with the superior pharyngeal constrictor and the middle pharyngeal constrictor muscles). The cricopharyngeus has an important sphincteric function. It acts as a sphincter at the lower end of the pharynx and is always closed except for momentary relaxation during swallowing. Its muscle fibers are continuous with the circular muscular coat of the esophagus. ![]() Its fibers run continuously from one side of the cricoid arch to the other side around the pharynx without inserting into a midline raphe posteriorly. The cricopharyngeus muscle is rounder and thicker than the other constrictor muscles. The lower fibers are horizontal and lie edge to edge with those of the cricopharyngeus component. Its fibers curve around posteriorly and insert into the midline raphe. The thyropharyngeus muscle arises from the (a) thyroid cartilage at the oblique line and (b) the tendinous arch that spans the cricothyroid muscle. ![]()
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