11.03.11+-+Larynx

Larynx


 * 1. Define the components of the respiratory layer of the cervical viscera.**

There are 9 cartilages, three paired: thyroid, cricoid, and epiglottic; and three unpaired: arytenoid, corniculate, and cuneiform. There are two sets of extrinsic muscles, the infra and supra hyoid muscles, along with sylopharyngeus. There are 7 intrinsic muscles, all innervated by the inferior laryngeal nerve except for the cricothyroid muscle. The 6 are the vocalis, thyro-arytenoid, posterior crico-arytenoid, lateral crico-arytenoid, transverse arytenoid, and oblique arytenoid.


 * 2. Describe the function and location of the larynx.**

The larynx has two major functions, the first is protection of the respiratory tract (especially during swallowing) and the second is phonation. The larynx connects the oropharynx to the trachea. It begins where the esophagus splits off of the oropharynx.


 * 3. Describe the cartilaginous structures that makeup the larynx and the relationship to the hyoid bone.**

Inferior to the hyoid the thyrohyoid ligament connects to the thyroid cartilage. Inferior to the thyroid cartilage, the median cricothyroid ligament connects the thyroid cartilage to the cricoid cartilage on the anterior median line. The lateral cricothyroid ligament extends superiorly and medially from the lateral edges of the cricoid cartilage toward the center of the larynx and form the vocal ligament. The cricoid cartilage is the only complete cartilaginous ring around the breathing tube. On the posterior side of the cricoid cartilage the arythenoid cartilages extend superiorly. The corniculate and cuneiform cartilages are further more minor extensions. Superior to the aretenoid cartilage the aryepiglottic membrane attaches to the inferior surface of the epiglottic cartilage.


 * 4. Describe the interior of the larynx and the underlying structures that create visual landmarks (e.g. vocal and vestibular folds)**

The interior of the larynx is covered by mucous membrane. The vestibular fold is superior to the vocal fold. Inbetween the folds is the laryngeal ventricle. The space within the larynx superior to the vestibular fold is the laryngeal vestibule. The middle part of the laryngeal cavity is the space at the intersection of the vestibular folds and the vocal folds. And the space within the larynx below the vocal cords is called infraglottic cavity.


 * 5. Describe the extrinsic and intrinsic muscles of the larynx and their action on the various bony, cartilaginous structures and ligaments.**

The extrinsic muscles can be divided into supra hyoid and infra hyoid. The supra hyoid muscles are digastric, mylohyoid, geniohyoid, and stylohyiod. The infra hyoid muscles are sternohyoid, omohyoid, thyrohyoid, and sternothyroid. The supra hyoid muscles move the hyoid in the direction to which they attach (generally superiorly). They contract during swallowing to elevate the hyoid and close the larynx with the epiglottis. There is one other extrinsic muscle called the stylopharyngeal muscle.

The intrinsic muscles move pieces of the larynx with respect to each other. They are mostly active during phonation and swallowing. During swallowing all of the muscles flex to act as a sphincter that protects the trachea from whatever substance is being swallowed. The cricothyroid is attached between the cricoid and thyroid cartilages. It depresses the thyroid cartilage and stretches the vocal cords. The thyro-aretenoid runs within the larynx just laterally to vocalis. When it contracts the vocal cords relaxed. The posterior crico-arytenoid abducts the vocal cords by laterally rotating the arytenoid cartilages. The lateral crico-arytenoid adducts the vocal cords by medially rotating the arytenoid cartilages. The transverse and oblique arytenoids work together to also adduct the vocal cords. The vocalis is active during phonation.


 * 6. Describe the nervous innervation of the larynx and consequences of damage or block of specific nerves.**

The inferior pharyngeal nerve (the terminal branch of the recurrent pharyngeal nerve) innervates all of the intrinsic muscles except for the cricothyroid muscle, which is innervated by the external branch of the superior pharyngeal nerve. The supra hyoid muscles are innervated by all different nerves. The nerve to mylohyoid, a branch from V3, innervates mylohyoid and the anterior belly of digastric. Muscular branches from the facial nerve innervate both the stylohyoid and the posterior belly of digastric. Geniohyoid is innervated by cervical nerves that hitchhike on hypoglossal nerve. The infra hyoid muscles are innervated by muscular branches of cervical plexus via ansa cervicalis (except for thyrohyoid branch which hitchhikes on hypoglossal nerve.

Inability to speak/swallow.


 * 7. Contrast the role of larynx in deglutition in the adult and newborn.**

In adults the larynx is fully shut during deglutition by the epiglottis and flexure of the intrinsic muscles of the larynx.

In newborns the laryngopharynx is sealed from the nasopharynx by the epiglottis during deglutition. Somehow swallowing and breathing occur simultaneously.


 * 8. Describe the blood supply and lymphatic drainage of the larynx.**

The larynx is subserved by the superior and inferior thyroid arteries via the superior and inferior laryngeal arteries. The cricothyroid muscles gets its own artery, a branch from the superior thyroid artery. Lymph nodes superior to the vocal cords drain to the superior deep cervical lymph nodes. Inferior to the vocal folds drain to the inferior deep cervical lymph nodes.


 * 9. Describe the structures seen when viewing the larynx prior to intubation or endoscopy.**

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 * 10. Describe the safest approach to tracheostomy based on your knowledge of the structures.**

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