The function and Structure of the Larynx

what is the function of the larynx?

• guard the entrance of the trachea to prevent coarse material from entering

• control passage of air in and out of trachea

• act of swallowing

what is the structure of the larynx?

a musculo-cartilagenous organ

what are the components of the larynx?

1. laryngeal cartilage

2. laryngeal muscles

3. ligaments, membranes, and folds

4. glottic cleft

what is the location of the larynx in reference to the tongue?

caudal

what is the location of the larynx in reference to the trachea?

cranial

where can you palpate and access the larynx?

from the ventral neck (throat region)

what structure is the arrow pointing to on the left?

larynx

what structure is the arrow pointing to on the right?

thyroid gland

what structure is A?

soft palate

what structure is B?

larynx

what structure is C?

guttural pouch

what structure is D?

laryngopharynx

what is the only paired cartilage in the larynx?

arytenoid cartilage

what is the only cartilage of the larynx that is completely closed and creates a ring structure?

cricoid cartilage

in the dog at the ventral aspect, what happens with the thyroid cartilage?

it is completely fused lamina from left and right side

what is the shape of the thyroid cartilage?

“U” shaped

in the horse at the ventral aspect of the thyroid cartilage what is happening?

there is a gap between laminae

which cartilage of the larynx is related to the caudal edge of the soft palette?

epiglottic cartilage

which cartilage of the larynx has a rostral and caudal horn?

thyroid cartilage

describe the epiglottic cartilage in the horse

• more curved

• always over the caudal edge of soft palette (other than swallowing)

• cuneiform processes

describe the thyroid cartilage of the horse

• longer

• prominent rostral and caudal horns

• deep notch exists on caudal and ventral aspect

• laminae are fused only cranially

describe the arytenoid cartilage of the horse

cuneiform process not present

list the laryngeal cartilages in the horse

• epiglottic cartilage

• thyroid cartilage

• arytenoid cartilage

• cricoid cartilage

which nerve provides nerve supply to most of the intrinsic muscles including cricoarytenoideus dorsalis muscle?

caudal laryngeal nerve

what is structure 1?

recurrent/caudal laryngeal nerve

what is structure 2?

cranial thyroid artery

what is structure 3?

cranial laryngeal artery and nerve

what does the cranial laryngeal nerve innervate?

cricothryoideous muscle

what does the glossopharyngeal nerve innervate?

related to extrinsic muscles of the larynx via pharyngeal plexus

hypoid apparatus

set of bones that connect the larynx to the skull

what is the function of the hypoid apparatus?

1. support larynx

2. function like a spring to bring larynx back into place

3. support tongue

is the thyrohyoid bone paired or unpaired?

paired

where is the thyrohyroid bone located?

attached to rostral horn of thyroid cartilage

is the basihypoid bone paired or unpaired?

unpaired

where is the basihypoid bone located?

transversley oriented at the baseof the tongue, between the thyrohyoid bones.

what does the basihyoid bone have in the horse?

lingual process

is the ceratohyoid bone paired or unpaired?

paired

is the epihyoid bone paired or unpaired?

paired

the epihyoid bone in horses is

rudimentary

which bone of the hyoid apparatus makes contact with the skull?

stylohyoid bone

is the stylohyoid bone paired or unpaired?

paired

explain the stylohyoid bone in horses

very large and runs transverse in guttural pouch to divide pouch into lateral and medial component

explain the hyoid bone in case of ruminants

hyoid bone going to have an extension more rostrally where tongue is attached to basihyoid bone

what is 1?

tympanohyoid cartilage

what is 2?

stylohyoid bone

what is 3?

epihyoid

what is 4?

epiglottis

what is 5?

thyrohyoid

what is 6?

ceratohyoid

what is 7?

basihyoid

what is 8?

thyroid cartilage

what is 9?

cuneiform process of arytenoid cartilage

what is 10?

sesamoid cartilage

what is 11?

interarytenoid cartilage

what is 12?

cricoid cartilage

which direction is the larynx pulled during contraction?

backwards

list the extrinsic muscles of the larynx

• sternothyroideus muscle

• thyrohyoideus muscle

• hyoepiglotticus muscle

• cricopharyngeus muscle

• thyropharyndeus muscle

thyrohyoid articulation

thyrohyoid bone will attache to thyrohypoid cartilage

cricothyroid articulation

caudal horn of thyroid cartilage will attache with little lateral aspect of cricoid cartilage

cricoarytenoid articulation

caudal end of arytenoid cartilage will connect to cranial edge of cricoid cartilage

what is the function of the sternothyroideus muscle?

move larynx backward with cranial nerve 11

what is the function of the thyrohyoideus muscle?

move larynx forward (hypoglossal nerve (12))

what is the function of the hyoepiglotticus muscle?

move larynx forward (hypoglossal nerve (12))

what is the function of the cricopharyngeus muscle?

• connect larynx and laryngopharynx

• constricts laryngopharynx (vagus nerve + CN 12)

what is the function of the thyropharyngeus muscle?

• constricts laryngopharynx and assists in swallowing (vagus nerve + CN 12)

• connect larynx and laryngopharynx

what is the only muscle that ABDUCTS arytenoid cartilage and opens glottic cleft?

cricoarytenoid dorsalis

cricoarytenoideus lateralis

an adductor of the vocal processes and thus NARROWS the glottis

thyro-arytenoideus

associated with the vocal and vestibular folds

what clinical condition involves paralysis of the laryngeal muscles on the left/right side only?

laryngeal hemiplegia

what are clinical signs of aryepiglottic fold collapse?

exercise intolerance and noise with exercise

what leads to aryepiglottic fold collapse in horses?

• negative pressure in upper airways lead to collapse

• tissue between the epiglottis and larynx pulled into the airway

laryngeal hemiplegia

degeneration of laryngeal branch of vagus nerve leads to neurogenic atrophy of cricoarytenoideus dorsalis muscle

what side is more common in horses for laryngeal hemiplagia?

left

what is the longest nerve in the body?

laryngeal branch of the vagus nerve

dorsal displacement. of the soft palette is seen in which species?

horses

what occurs physiologically in dorsal displacement of the soft palette?

soft palette lies over the epiglottic cartilage blocking the laryngeal inlet and airways

what are the effects of dorsal displacement of the soft palette?

respiratory distress and performance issues

what is the arrangement of the soft palette in the dog?

caudal margin of the soft palette just makes contact with the epiglottic cartilage

what is the arrangement of the soft palette in the horse?

soft palette always lies beneath the epiglottic cartilage

what can horses not do, due to the arrangement of their soft palette?

• emesis (vomit)

• mouth breath (they are obligate nasal breathers)

what is it called if paralysis of the laryngeal muscle only occurs on one side?

laryngeal hemiplegia

what is it called if paralysis of the laryngeal muscle occurs on both side?

laryngeal paraplegia

what forms the glottic cleft?

media, side-by-side arrangement of arytenoid cartilages

what closes the glottic cleft?

adduction of the arytenoid cartilages

what is the glottic cleft important for?

• closing the entrance to the trachea

• normal smooth inspiration and expiration of breath

what opens the glottic cleft?

abduction of the arytenoid cartilage

what is the ONLY muscle that opens the glottic cleft?

cricoarytenoideus dorsalis

what are the components of the larygneal cavity?

• vestibule

• glottis

• infraglottic space

what is the function of the laryngeal cavity?

receives sensory innervation from cranial and caudal (recurrent) laryngeal nerves

laryngeal ventricles

lateral extension/blind sacs of the lumen

what is not present in the cat in the laryngeal cavity?

left laryngeal ventricle

what is the green shaded area?

vestibule of laryngeal cavity

what is the purple shaded area?

glottis of laryngeal cavity

what is the pink line referring to?

vestibular fold of laryngeal cavity

what is the blue line referring to?

vocal fold

what is the red shaded area referring to?

infraglottic space

which opening can be closed by backward closing of the epiglottic cartilage?

aditus laryngis

what is the only laryngeal intrinsic muscle that is innervated by the cranial laryngeal nerve?

cricothyroid muscle