LARYNX POWERPOINT SERIES Prepared by Dr A Horowitz IT assistance from Mr. Paul Orchard and Mr. Kimbel Jeffers

Equine larynx: 5 cartilages. 1 Epiglottic, 2 Arytenoid, 1 Thyroid, 1 Cricoid. E A, A T C

Equine larynx, left lamina of thyroid cartilage removed, showing muscles. laryngeal ventricle

With these cartilages and muscles, the larynx does two things: 1. Regulates the passage of air… 2. Determines the pitch of the voice… How does it regulate the passage of air?

It regulates the passage of air by changing the size of the rima glottidis (also called “rima” or “glottic cleft”), even closing it completely. What is the rima glottidis? The rima is the diamond shaped space bounded by the vocal folds ventrally, the mucosa- covered arytenoid cartilages dorsally.

mucosa-covered arytenoid cartilages mucosa of the vocal folds rima glottidis Epig. From Budras Atlas

Diagram of the rima glottidis, (also called “glottic cleft” or “rima”) arytenoid cartilages laryngeal mucosa vocal lig. vocalis muscle

Vocal Fold = vocal lig. + vocalis muscle + muscosa covering them

Arytenoid cartilage doesn’t stretch. The elastic vocal ligament will. Abduction of the vocal process of the cartilage widens the rima..

Resting position of the rima…

Enlarged rima with each inspiration…

Rima changes in each respiratory cycle…

The rima nearly closed…(pic from Budras Atlas of Anatomy of the Horse)

Cricoid cartilage: like a signet ring, has a lamina and an arch lamina arch lamina arch articulate w/R and L arytenoid carts. articulate w/caudal cornu of thyroid cart.

The thyroid cartilage articulating with the cricoid… jt.

Right view with right lamina of thyroid cartilage, right half of epiglottic cart., and right vestibular ligament cut away. CA, A E vestib. ligg. vocal ligg. T vocal process

caudal cornu (thyroid cart) cricoarytenoideus dorsalis m. cricaryt jt musc proc arc crest vocal proc cornic proc med crest medial proc One muscle widens the rima glottidis: cricoarytenoideus dorsalis

Note that, in the preceding slide, as the muscular process of the arytenoid cartilage is drawn caudomedially by contraction of the cricoarytenoideus dorsalis muscle, the vocal process moves rostrolaterally. This widens the rima in inspiration. The muscles that close the rima, return it to the resting position with each expiration. These movements occur reflexly with each respiratory cycle.

vocal ligg. vocal proc. “body” of thyroid cart. Arrows: movement of musc. and vocal procc.

How the rima is closed… 2. thyroarytenoideus contracts 1. arytenoideus transversus contracts 3. vocal processes adducted

The arytenoideus transversus (dorsally) and the thyroarytenoideus (laterally and ventrally), contracting simultaneously, act as a sphincter, closing the rima. The cricoarytenoideus lateralis cooperates in this action.

How the rima is closed… 3. cricoaryt. lat. contracts thyroaryt. (vocalis part, cut)

How does the larynx regulate pitch of the voice? By changing the tension of the vocal fold: done by contraction of the cricothyroideus muscle, chiefly… cricothyroideus resting (lower pitch)

cricothyroideus m.

Cricothyroideus muscle contracting stretches the vocal folds (only vocal ligg. shown here)… vocal ligg.

An animal with laryngeal dysfunction would be expected to have difficulty a. breathing; b. regulating the pitch of its sound; c. utilizing the abdominal press (which, to be fully effective, requires that the rima glottidis be completely closed).

Main (not the only ones) clinical syndromes… -laryngeal hemiplegia; -dorsal displacement of the soft palate (DDSP); -epiglottic entrapment.

Laryngeal hemiplegia (paralysis of the right or left recurrent laryngeal nerve)…Which side is paralyzed?

Recurrent laryngeal nerve ends as the caudal laryngeal nerve; Supplies all laryngeal muscles except cricothyroideus & is sensory to caudal larynx; Cranial laryngeal nerve or pharyngeal branch of the vagus supplies the cricothyroideus; chief sensory nerve. What muscle must be paralyzed with inability to abduct the vocal fold?

Techniques for treating laryngeal hemiplegia: 1.Electrocautery excision of vocal fold; 2.Surg. removal of the laryngeal ventricle with repair by elastic connective tissue; 3.Fixing the arytenoid cartilage in an abducted position; a nonabsorbable suture is used; 4.Nerve transplant.

In a mature horse, in normal respiration, the larynx protrudes into the intrapharygeal ostium. soft palate Figure is from Sisson.

DDSP: From Budras Atlas of the Anatomy of the Horse soft palate Palato- pharyngeal arch

Epiglottic entrapment… aryepiglottic fold (aef) aef extending in front of epiglottis aef folding over the apex of the epiglottis aef

The abdominal press (a physiological mechanism to increase abdominal pressure)… 1.Animal takes a deep breath; diaphragm moves caudally, abdl muscles relax; 2.Rima glottidis is closed (what muscles?); 3.Abdl muscles contract (abdl pressure ); 4.Rima opens (what muscles?) and animal coughs; or rima closed, fetus expelled…

Normal larynx viewed with the endoscope from within the nasal pharynx…Can you I.D. the “rima”? Ans: roof of nasal pharynx Ans: soft palate vocal fold vestibular fold laryng. ventric. This is the roof of the nasal pharynx.

The laryngeal ventricle: a lateral evagination of the laryngeal mucosa; between the vocal fold caudally, the vestibular fold rostrally. A higher pitched sound as the mass of the vocal fold is less. laryngeal ventricle Figure is from Sisson.

Interior of the horse’s larynx… vestibulerimainfraglottic cavity laryngeal ventric. vestibular fold vocal fold

Cricothyroid ligament is an important access to the larynx.

Photo taken from 5 th semester diagnostic imaging presentation on equine throat… What’s this? this? Be a supervet!

SWALLOWING… WHAT HAPPENS?

RESTING PHARYNX

BOLUS DOES NOT CONTACT THE EPIGLOTTIS, WHICH IS PUSHED BENEATH THE ARCHING TONGUE.

In normal swallowing, the bolus does not contact the epiglottic mucosa. What happens if it does? The animal coughs reflexly. Contact of the bolus with tactile mucosal receptors initiates the cough reflex. What is responsible for your cough when you swallow and the food “goes down the wrong way”?