Larynx & Hyoid Apparatus

Question 1

List the structures of the hyoid apparatus

Answer 1

1. Basihyoid - Unpaired bone.
2. Stylohyoid - Articulates with base of skull at the petrus temporal. A paired bone.
3. Epihyoid - A paired bone.
4. Keratohyoid - A paired bone.
5. Thyrohyoid - Articulates with the thyroid cartilage of the larynx. A paired bone.

Question 2

Describe the function of the hyoid apparatus

Answer 2

Larynx is suspended by the hyoid bones which articulate with the base of the skull (temporal bones)

Linked together by either synovial or cartilaginous joints

It provides the mechanism to move the larynx back and forth in the aid of swallowing
Human dont have one as gravity moves the larynx down for us

Question 3

Outline the species difference of the hyoid apparatus and larynx in dogs

Answer 3

Stylohyoid bones are not palpable.

Question 4

Outline the species difference of the hyoid apparatus and larynx in equidae

Answer 4

Epihyoid is small, the lingual process is present and they have a well developed stylohyoid muscle.

Question 5

Outline the species difference of the hyoid apparatus and larynx in bovidae

Answer 5

Lingual process is present (shorter than in horse)
Epihyoid & stylohyoid are equal size

Apparatus are similar to horse

Question 6

Outline the species difference of the hyoid apparatus and larynx in pigs

Answer 6

Usual pattern - Lingual process is present.

Short Epihyoid

Arytenoids appear to be double up on each side due to presence pf corniculate cartilages unique to the pig

Question 7

Outline the location of the larynx

Answer 7

Ventral to laryngopharynx (start of oesophagus)

Caudal to tongue

Suspended by hyoid apparatus

Caudal to jaw (easy to palpate)

Horse, ruminant & birds it is between the rami of the mandible

Carnivores, pigs, humans it is located in the neck

Question 8

Describe the function of the larynx

Answer 8

Connection of nasopharynx and trachea

Role in breathing/respiration

Protection of the lower airways

Role in swallowing

Phonation (birds use their syrinx)

Question 9

Briefly describe the histology of the larynx

Answer 9

Stratified squamous mucosa (Epithelium + Lamina Propria) at the entrance (epiglottis) and on the vocal folds.

Other areas are made of pseudostratified ciliated mucosa

Question 10

Describe the palpable landmarks of the larynx

Answer 10

Thyroid Cartilage cranio-ventral in the middle

Cricoid cartilage caudoventral

First cartilage of trachea

Question 11

What structures is the larynx formed of?

Answer 11

Collagenous & elastic ligaments

Striated Musculature

Mucous Membrane

Vessels

Nerves

Question 12

Explain the suspension of the larynx and articulation with the hyoid apparatus

Answer 12

Thyroid Cartilage
Hyaline cartilage and forms most of the floor of the larynx.
Fusion of the two lateral plates varies in different species.
Rostral part forms the ‘Adam’s apple’.
Articulates with the thyrohyoid bone and the cricoid cartilage. It becomes brittle as the animal ages.

Cricoid Cartilage
Hyaline cartilage.
Signet ring shaped and is wider on the dorsal surface than the ventral surface.
There is a crest on the midline of the dorsal surface and facets for arytenoid cartilages on the rostral edge.
Articulates with the thyroid cartilage. It also becomes brittle as the animal ages.

Arytenoid Cartilage
Hyaline cartilage (also contains elastic cartilage)
Paired and articulates with the rostral part of the cricoid cartilage.
A vocal process is present on the caudal surface where the vocal folds attach; a muscular process extends laterally and a corniculate process extends dorsomedially.

Question 13

How is the hyoid apparatus connected between itself, the trachea and hyoid bones

Answer 13

Connected by:
Joints - cartilaginous or synovial
Cricoarytenoid joint (synovial)
Cricothyroid joint (synovial)

            Collagenous & elastic ligaments
                  Rostral is the vestibular ligament (vestibular fold (3))
                  Caudal is the vocal ligament (vocal fold (4))

           Striated musculature
                  	Extrinsic connects the larynx to hyoid bones, pharynx and sternum
	         Involved in swallowing

Question 14

Outline the different ways of accessing the larynx

Answer 14

Entrance to the larynx Þ Vestibule (medianus recess (horse, pig))

Glottis (lateral ventricle (dog, horse, pig), glottic cleft)

Infraglottic cavity

Question 15

Describe Hobdays Operations

Answer 15

Provides access to the ventral aspect of the larynx on a horse

The laryngeal ventricles and vocal cord are removed surgically to encourage scarring. The scar tissue acts to stabilise the area and prevents the vibrations in the larynx

This is to stop whistling in horses

Question 16

Explain the function of the larynx and its effects of conduction of air to the lungs and deglutition

Answer 16

The larynx protects the trachea in swallowing, preventing aspiration of foreign material. During swallowing, the larynx is moved rostrally causing the epiglottis to partially cover the laryngeal entrance. Solid foods are carried over the laryngeal entrance by the muscles of the pharynx. Fluids are deflected by the epiglottis. Closure of the glottis also prevents food passing down the larynx. The reflex stimulation of the mucosa promotes the coughing reflex.

The larynx also allows the passage of air to the lungs and increases the intra-abdominal pressure. The glottis can widen by adduction of the vocal folds when breathing is vigorous. In addition to this, the larynx is used for vocalisation

Question 17

Explain the innervation the larynx muscles and their effects of conduction of air to the lungs and deglutition

Answer 17

The larynx is innervated by a branch of XI which travels with the descent of the vagus nerve (CN X).

Cranial laryngeal nerve has two branches which arise from CN X.
The internal branch innervates the mucosa and the external branch innervates the
cricothyroid muscle and constricts the pharynx.

Caudal (recurrent) laryngeal nerve (XI) innervates the intrinsic muscles of the larynx (except the cricothyroid muscle).

Question 18

Describe the intrinsic musculature of the larynx during widening of the glottis

Answer 18

Cricoarytenoids dorsalis (2)
The only muscle that widens the glottis
Supplied by recurrent laryngeal nn.

Question 19

Outline the clinical relevance of the Cricoarytenoids dorsalis (2)

Answer 19

Left laryngeal hemiplegia when left nerve is damaged

Leading to inspiratory noise & poor performance

Can feel the wasted muscle & fails the slap test

Question 20

Describe the intrinsic musculature of the larynx during narrowing of the glottis

Answer 20

Cricothyroid (1)

Arytenoideus transversus (6)

Cricoarytenoideus lateralis (3)
Closes the glottis

Thyroarytenoideus:
Ventricularis (5)
Vocalis (4)

Question 21

What is the clinical relevance of Laryngoscopy?

Answer 21

View any abnormalities of the larynx

Example:
Horse making a continuous roaring or whistling sound during inspiration at exercise. Endoscopy present abnormalities of left vocal fold and left arytenoid.

Diagnosis: Left laryngeal hemiplegia

Question 22

Outline the structure of a birds larynx and hyoid apparatus

Answer 22

Consists of cricoid and arytenoid cartilages

No vocal folds => no creation of sound

Glottis can be closed to prevent food particles to enter larynx / trachea