Larynx

=**Objectives**=

The cartilagenous skeleton of the larynx consists of three paired and three unpaired cartilages:
 * 1. Describe the cartilagenous skeleton of the larynx.**

Unpaired cartilages:

Thyroid cartilage- This is the largest cartilage in the larynx. It consists of hyaline cartilage. It articulates with the epiglottis at the superior thyroid notch, and has superior and inferior horns. The inferior horns articulate with the cricoid cartilage at a synovial joint. It is an incomplete ring. Its two plates, or "laminae", meet at the midline to form the laryngeal prominence.

Cricoid cartilage- This hyaline cartilage articulates synovially with the inferior horn of the thyroid cartilage and is a complete ring. It is "signet ring shaped", with a wider 'quadralateral plate' posteriorly, and a narrow 'anterior arch' anteriorly. Has facet for articulation with the arytenoid cartilages postersuperiorly, and a facet for articulation with the inferior horn of the thyroid cartilages inferoanteriorly.

Epiglottic cartilage- Unlike the other two, this is fibroelastic cartilage. It is attached to the thyroid notch superiorly by a ligament, at the internal thyroid cartilage.

Paired Cartilages: Arytenoid cartilage- a paired pyramidal set of cartilages (boot shaped) with an anterior vocal process, and a lateral muscular process. Articulates inferiorly with the cricoid cartilage at its base and superiorly with the small corniculate cartilage at its apex.

Corniculate cartilages are a small extension of the apex of the arytenoid cartilages. Cuneiform cartilages are embedded in the membrane covering the larynx.

The outer membranes: Thyrohyoid membrane: Joins the hyoid bone to the thyroid cartilage, meaning that any muscle acting on the hyoid bone has the same action on the thyroid cartilage. Runs vertically, connecting the thyroid cartilage to the hyoid bone anteriorly and laterally. The medial anterior part is thickened, and named "medial thyrohyoid membrane".
 * 2. Explain the orientation of the membranes that act to support the cartilages of the larynx.**

Cricothyroid membrane: connects the cricoid cartilage and thyroid cartilage.

Cricotracheal membrane: connects the inferior margin of the cricoid to the first tracheal ring.

The inner membranes: Quadrangular membrane: connects the lateral inferior border of the epiglottis to the anterolateral border of each arytenoid cartilage. The free inferior margin of the membrane is known as the "vestibular ligament"(false vocal ligament).

Conus Elasticus- Drapes down from vocal ligaments to the superolateral aspect of the cricothyroid cartilage.


 * 3. Describe the internal anatomy of the larynx. Where are the vestibular folds? Where are the vocal folds?**

The internal portion of the larynx is divided into three chambers by the above listed inner membranes and two major ligaments covered with mucosa, to create folds. The two folds are(paired): Vestibular fold- oriented in the inferior margin of the quadrangular membrane. Vocal Fold- stretches from the vocal process of each arytenoid cartilage to the superomedial aspect of the thyroid cartilage.

The three chambers are: Vestibule: The space superior to the vestibular fold. Ventricle: The space between the vestibular and vocal folds. Infraglottic cavity: The space inferior to the vocal folds.

The rima glottis is defined as the space between the paired vocal folds.

All intrinsic laryngeal muscles are innervated by branches of the vagus. All are innervated by the recurrent branch, with the exception of the cricothyroid muscle, which is innervated by the external branch. Posterior cricoarytenoid: O: posterior aspect of cricoid I: Muscular process of arytenoid A: Abducts vocal fold, opening rima glottis (pivot action)
 * 4. Explain the location, innervation, and action of each of the intrinsic muscles of the larynx.**

Lateral cricarytenoid: O: lateral cricoid I: Muscular process of arytenoid A: Adduction of vocal fold, closing rima glottis (pivot)

Transverse and oblique arytenoids(double bellied): Origin and Insertion on arytenoid cartilage. A: Pulls the two arytenoids together, adducting them. (Gliding)

Thyroarytenoid: O: Thyroid cartilage I:Vocal Process A: pulls thyroid cartilage posteriorly, loosening the vocal folds

Cricothyroid: O: I:Vocal Process A: Tips thyroid cartilage forward, tensing vocal ligaments


 * 5. Review the blood supply and innervation to the mucous membranes that line the larynx.**

The larynx above the Vocal folds receives innervation from the internal and external laryngeal nerves which are branches of the superior laryngeal nerve. The internal laryngeal nerve supplies sensory innervation to the mucosa and visceral motor innervation to the glands of the mucosa. The external laryngeal nerve supplies motor innervation the cricothyroid and inferior constrictor muscles. Blood is supplied by the superior laryngeal artery a branch of the superior thyroid. The larynx below the vocal fold receives innervation from the inferior laryngeal nerve, the terminal end of the recurrent laryngeal nerves. It supplies the intrinsic laryngeal muscles, sensory to the mucosa, and motor innervation to the glands of the mucosa. The blood supply is from inferior laryngeal arteries a branch of inferior thyroid.


 * 6. Explain how the larynx works during phonation. What anatomical features of the larynx may affect the quality of your voice?**

The larynx uses the true vocal folds, which run between the vocal process of the arytenoid cartilages to the anterior surface of the thyroid cartilage, to produce sound during exhalation. The vocal cords are placed in close proximity by the process of adduction which narrows the rima glottidis producing sound as air passes. The tension on the vocal folds can be varied by moving the thyroid cartilage adjusting the pitch of sound produced. The tension on the cords, the size of the structures of the larynx, can vary the quality of the voice, i.e. deeper voice in men due to larger thicker larynx.