Larynx Flashcards
Larynx
The larynx (voice box) has two basic functions: to regulate the passage of materials through the airway (it acts like a valve), and for voice production. Superiorly it opens into the laryngopharynx; inferiorly it is continuous with the trachea
Laryngeal Skeleton
The skeleton of the larynx consists of nine cartilages (3 paired, 3 unpaired) joined by membranes and ligaments. The hyoid bone is not part of the larynx, but it serves a supportive function for some of the ligaments. The cartilages of the larynx are derived from the mesenchyme of the 4th and 6th pharyngeal arches.
Thyroid Cartilage
The thyroid cartilage is the large V-shaped cartilage that surrounds the anterior part of the larynx. It is suspended from the inferior border of the hyoid bone via the thyrohyoid membrane. Its two laminae meet in the anterior midline as the laryngeal prominence (Adam’s apple). It has superior horns and inferior horns.
Cricoid Cartilage
The cricoid cartilage is the only complete ring of cartilage that surrounds the airway. It is narrow anteriorly and wide posteriorly. The cricoid cartilage articulates with the inferior horns of the thyroid cartilage.
Epiglottis
The epiglottis is a leaf-shaped cartilage attached to the body of the hyoid bone and the internal surface of the thyroid cartilage. It forms the anterior border of the laryngeal inlet. During swallowing, the epiglottis moves inferiorly to cover the laryngeal inlet.
Arytenoid cartilage
The arytenoid cartilages are two small cartilages that resemble a pair of boots resting on the upper border of the cricoid cartilage. They have a:
• vocal process that projects anteriorly (for attachment of the vocal ligament) and
• muscular process that projects laterally (for attachment of muscles).
Movements of the Arytenoid
The arytenoids are highly mobile and can slide, rotate and tilt on the superior surface of the cricoid
Corniculate and Cuneiform cartilages
Two additional pairs of cartilages are found within the aryepiglottic folds – the corniculate and cuneiform cartilages. These have a supportive role; their position is indicated by the ‘round bulges’ in the aryepiglottic folds (corinculate is the more medial cartilage that rests on top of the arytenoid cartilage).
Thyrohyoid membrane
The thyrohyoid membrane is a wide membrane that connects the upper margin of the thyroid cartilage to the hyoid bone. On each side there is a small hole that transmits the superior laryngeal vessels and the internal laryngeal nerve.
Quadrangular membrane
The quadrangular membrane extends from the epiglottis to the arytenoid cartilage; it forms the aryepiglottic fold and the lateral wall of the entrance to the larynx. The lower free border of this membrane is the vestibular ligament (false vocal cord), which is found within the vestibular fold (fold = ligament + mucous membrane covering it).
Conus elasticus
The conus elasticus (aka cricothyroid ligament) connects the superior surface of the cricoid cartilage to the vocal process of the arytenoid cartilage and the internal midline of the thyroid cartilage. The superior, free edge is thickened and forms the true vocal ligament.
Median cricothyroid ligament
The mid-portion of the conus elasticus is called the median cricothyroid ligament. This ligament is incised during a cricothyrotomy.
Epiglottic ligaments
- Hyoepiglottic ligament anchors the epiglottis to the hyoid bone.
- Thyroepiglottic ligament anchors the epiglottis to the thyroid cartilage
Interior of the larynx
The interior of the larynx is covered by a mucous membrane derived from endoderm (the larynx is derived from the respiratory diverticulum). The epithelium is ciliated pseudostratified columnar
Laryngeal inlet
The laryngeal inlet (laryngeal aditus) is the opening into the larynx from the laryngopharynx. Its boundaries are the epiglottis anteriorly, the aryepiglottic folds laterally and the interarytenoid notch posteriorly.
Vestibular folds
The vestibular folds (i.e. false vocal cords) that consist of the vestibular ligaments surrounded by mucous membrane
Vocal folds
The vocal folds (i.e. true vocal cords) are likewise comprised of mucous membrane over the vocal ligaments, however there are also some muscle fibers within the folds called the vocalis muscles
Ventricles
The lateral recesses between the vestibular folds and vocal folds are called the ventricles. Each ventricle has an anterior projection called a saccule, which contains mucous glands that lubricate the vocal folds.
Vestibul
The vestibule is the area between the inlet and the vestibular folds
Glottis
The glottis (a.k.a. rima glottidis) is the space between the vocal cords.
Infraglottic cavity
The infraglottic cavity is the space inferior to the vocal cords and superior to the trachea.
Function of Laryngeal Muscles
Quiet Respiration
During quiet respiration the vocal cords are partially abducted (glottis open)
Function of Laryngeal Muscles
Forced Inspiration
Forced inspiration requires complete abduction of the vocal cords so that the glottis opens fully.
Function of Laryngeal Muscles
Phonation
During phonation the vocal folds are adducted; sound is produced when air from the lungs is forced up through the folds.
Function of Laryngeal Muscles
Effort Closure / Swallowing
Closure of the glottis occurs during “effort closure” (Valsalva maneuver) and during swallowing.
Function of Laryngeal Muscles
Swallowing
The laryngeal inlet narrows during swallowing to prevent food from entering the larynx.
Extrinsic muscles of the larynx
Extrinsic muscles of the larynx are muscles that move the larynx as a whole, rather than a specific part of the larynx. In general these muscles move the larynx by moving the hyoid bone (recall that the larynx is suspended from the hyoid bone).
They therefore include:
• Suprahyoid muscles
• Infrahyoid muscles
The position of the larynx in the neck also affects the pitch of the voice (by changing the size of the resonating chamber).
Suprahyoid muscles
Elevate Larynx
Muscles that elevate the hyoid and larynx are the suprahyoid muscles • geniohyoid • mylohyoid • digastrics • stylohyoid
Elevation of the larynx is important during swallowing.
Suprahyoid muscles
Depress Larynx
Muscles that depress the hyoid and larynx are the infrahyoid muscles: • sternohyoid • omohyoid • sternothyroid • thyrohyoid
Intrinsic muscles of the larynx
They Include: • Cricothyroid • Thyroarytenoid • Vocalis • Posterior cricoarytenoid • Lateral cricoarytenoid • Transverse arytenoid • Oblique arytenoid
Intrinsic muscles of the larynx are muscles that act on a specific part of the larynx. In general these muscles alter the length or tension of the vocal folds, or change the size or shape of the glottis.
Remember that the intrinsic muscles of the larynx are derived from the 4th-6th arches.
Cricothyroid
The cricothyroid extends between the cricoid and thyroid cartilages. It pulls the anterior part of the thyroid cartilage inferiorly, thus stretching the vocal folds and increasing the tension on them. Cricothyroid is innervated by the external branch of the superior laryngeal nerve (branch of vagus). Note that this is the only intrinsic muscle of the larynx that is not innervated by the recurrent laryngeal nerve.
Thyroarytenoid
The thyroarytenoid arises from the internal aspect of the thyroid cartilage and inserts on the lateral border of the arytenoid cartilage. This muscle is a sphincter of the vestibule and is innervated by the recurrent laryngeal nerve.
Vocalis
The vocalis extends between the arytenoid cartilage and the internal aspect of the thyroid cartilage; its medial portion attaches to the vocal ligament. The action of this muscles is to adjust the tension of the vocal fold. It is innervated by the recurrent laryngeal nerve.
Posterior cricoarytenoid
The posterior cricoarytenoid pulls the muscular process of the arytenoid toward the midline. Since the arytenoid rotate on the cricoid cartilage, this causes the vocal process of the arytenoid to move laterally, thus causing the vocal ligaments to move apart. Therefore, the posterior cricoarytenoid abducts the vocal fold. It is innervated by the recurrent laryngeal nerve.
Lateral cricoarytenoid
The lateral cricoarytenoid pulls the muscular process of the arytenoid cartilage laterally, causing the vocal process to move medially. Therefore, its action is to adduct the vocal fold. Lateral cricoarytenoid is innervated by the recurrent laryngeal nerve.
The Posterior cricoarytenoid and Lateral cricoarytenoid oppose each other since they pull on the arytenoid cartilage from opposite locations.
Transverse arytenoid
The transverse arytenoid extends between the two arytenoid cartilages. Its action is to move the arytenoid cartilages closer together, thus helping to close the posterior portion of the glottis. It is innervated by the recurrent laryngeal nerve.
Oblique arytenoid
The oblique arytenoid is similar to the transverse arytenoid as the muscle fibers also extend from one arytenoid to the other – the difference is the fibers are oriented in an oblique fashion rather than transverse. Some of the fibers of the oblique portion continue upward in the aryepiglottic fold and are called the aryepiglottic muscle. The oblique arytenoid and aryepiglottic muscles act as sphincters and reduce the size of the laryngeal inlet.
Blood supply to the larynx
The blood supply to the larynx is provided by the: • • superior laryngeal arteries,
• inferior laryngeal arteries
They are branches of the superior and inferior thyroid arteries respectively. The superior laryngeal artery travels through the hole in the thyrohyoid membrane with the internal laryngeal nerve. The inferior laryngeal artery ascends along the trachea with the recurrent laryngeal nerve, and enters the larynx at the inferior border of the inferior pharyngeal constrictor muscle.
Sensory innervation to the Interior of the Larynx
Sensory innervation to the interior of the larynx is provided by the:
• Internal branch of the superior laryngeal nerve: (area superior to the vocal folds)
• Recurrent laryngeal nerve: (the vocal folds and the area inferior to the vocal folds).
The mucosa of the vestibule is particularly sensitive to foreign objects; contact by such an object initiates a forceful cough reflex to expel the object.
Motor innervation of the Larynx
Almost all the muscles of the larynx are innervated by the recurrent laryngeal nerve. The exception is the cricothyroid muscle which is innervated by the external laryngeal nerve.
Left recurrent laryngeal nerve
It is important to remember the course of the left recurrent laryngeal nerve – the fact that it enters the thorax and loops around the aortic arch. If a patient presents with a “hoarse voice” , you have to consider pathology in the thorax.
