Larynx & Hyoid Apparatus Flashcards
List the structures of the hyoid apparatus
- Basihyoid - Unpaired bone.
- Stylohyoid - Articulates with base of skull at the petrus temporal. A paired bone.
- Epihyoid - A paired bone.
- Keratohyoid - A paired bone.
- Thyrohyoid - Articulates with the thyroid cartilage of the larynx. A paired bone.
Describe the function of the hyoid apparatus
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
Outline the species difference of the hyoid apparatus and larynx in dogs
Stylohyoid bones are not palpable.
Outline the species difference of the hyoid apparatus and larynx in equidae
Epihyoid is small, the lingual process is present and they have a well developed stylohyoid muscle.
Outline the species difference of the hyoid apparatus and larynx in bovidae
Lingual process is present (shorter than in horse)
Epihyoid & stylohyoid are equal size
Apparatus are similar to horse
Outline the species difference of the hyoid apparatus and larynx in pigs
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
Outline the location of the larynx
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
Describe the function of the larynx
Connection of nasopharynx and trachea
Role in breathing/respiration
Protection of the lower airways
Role in swallowing
Phonation (birds use their syrinx)
Briefly describe the histology of the larynx
Stratified squamous mucosa (Epithelium + Lamina Propria) at the entrance (epiglottis) and on the vocal folds.
Other areas are made of pseudostratified ciliated mucosa
Describe the palpable landmarks of the larynx
Thyroid Cartilage cranio-ventral in the middle
Cricoid cartilage caudoventral
First cartilage of trachea
What structures is the larynx formed of?
Collagenous & elastic ligaments
Striated Musculature
Mucous Membrane
Vessels
Nerves
Explain the suspension of the larynx and articulation with the hyoid apparatus
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.
How is the hyoid apparatus connected between itself, the trachea and hyoid bones
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
Outline the different ways of accessing the larynx
Entrance to the larynx Þ Vestibule (medianus recess (horse, pig))
Glottis (lateral ventricle (dog, horse, pig), glottic cleft)
Infraglottic cavity
Describe Hobdays Operations
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
Explain the function of the larynx and its effects of conduction of air to the lungs and deglutition
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
Explain the innervation the larynx muscles and their effects of conduction of air to the lungs and deglutition
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).
Describe the intrinsic musculature of the larynx during widening of the glottis
Cricoarytenoids dorsalis (2)
The only muscle that widens the glottis
Supplied by recurrent laryngeal nn.
Outline the clinical relevance of the Cricoarytenoids dorsalis (2)
Left laryngeal hemiplegia when left nerve is damaged
Leading to inspiratory noise & poor performance
Can feel the wasted muscle & fails the slap test
Describe the intrinsic musculature of the larynx during narrowing of the glottis
Cricothyroid (1)
Arytenoideus transversus (6)
Cricoarytenoideus lateralis (3)
Closes the glottis
Thyroarytenoideus:
Ventricularis (5)
Vocalis (4)
What is the clinical relevance of Laryngoscopy?
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
Outline the structure of a birds larynx and hyoid apparatus
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
