CAR 7 - Larynx and Hyoid Apparatus

What is the larynx?

A cartilaginous tube which acts as a valve:

- Ventral to laryngopharynx

- Caudal to tongue

What is the larynx suspended by?

Hyoid apparatus

List the functions of the larynx.

- Breathing/respiration

- Protection/respiration

- Swallowing

- Straining

- Coughing

- Formation of voice (phonation)

What is the hyoid apparatus?

A set of bones linked by cartilaginous joints that act as a suspensory mechanism for the tongue and larynx:

- Dorsally attached to the temporal bone of the skull

- Ventrally attached to the larynx and base of tongue

Describe the structures of the hyoid apparatus in dogs and cats.

Tympanohoid

Stylohoid

Epihyoid

Ceratohyoid

Basihyoid

Thyrohyoid

Describe the structures of the hyoid apparatus in horses.

- Tympanohyoid

- Stylohoid

- Epihyoid

- Ceratohyoid

- Lungual process

- Basihyoid

- Thyrohyoid

- Thyroid cartilage

- Arytenoid cartilages

- Cricoid cartilage

How does the hyoid apparatus differ in bovines?

- Shorter lingual process

- Equal size epihyoid and stylohoid

Describe the soft tissue components of the larynx.

- Hyaline and elastic cartilage

- Collagenous and elastic ligaments

- Striated muscle

- Mucous membranes

- Vessels

- Nerves

Describe the cavities of the larynx.

- Entrance to larynx (orange)

- Vestibule (red)

- Glottis (green)

- Infraglottic cavity (purple)

Describe the mucosa of the larynx.

- Stratified squamous epithelium at entrance and on folds

- Pseudostratified ciliated epithelium elsewhere

- Lamina propria

Describe the cartilages of the larynx.

Hyaline cartilages:

- Thyroid

- Cricoid

- Arytenoids

Elastic cartilage:

- Epiglottis

Describe the cartilage connections of the larynx.

- Connect between themselves

- Connect to the trachea and hyoid bones

- Cartilaginous joints, ligaments, and striated musculature

- Cricoarytenoid joint

- Cricothyroid joint

- Vestibular ligament in the vestibular fold

- Vocal ligament in the vocal fold

Anything 'crico-' in the larynx is connected to what?

Tracheal ligament

Anything 'dorsal crico-' is connected to what?

Arytenoid muscles

Describe the palpable landmarks of the larynx.

- Thyroid cartilage

- Cricoid cartilage

- First tracheal cartilage

Describe the muscles of the larynx.

Intrinsic muscles between laryngeal cartilages are involved in respiration and phonation:

Dorsal cricoartenoid (2) wides the glottis

Cricothyroideus (1) narrows the glotts

Lateral cricoartyenoid (3) narrows and closes the glottis

Extrinsic muscles connect the larynx to hyoid bones, pharynx, and sternum and are involved in swallowing:

Why is the dorsal cricoarytenoid muscle clinically relevant?

- Only muscle that widens the glottis

- Supplied by recurrent laryngeal nerve

- Relevant for left laryngeal hemiplagia

- Left nerve becomes disease

- Inspiratory noise

- Poor performance

- Muscle wastage

Describe the innervation of the larynx.

Cranial laryngeal nerve

- From vagus (X)

- Cricothyroideus innervation

Recurrent (caudal) laryngeal nerve

- From accessory (XI)

- Innervation of all laryngeal muscles except cricothyroideus

Describe the route of the recurrent laryngeal nerves.

- Travel with descending vagus

- Left arches around the aorta

- Right around the right subclavian artery

- Both run lateral along the trachea to larynx

Describe how the airways are protected during swallowing.

- Larynx drawn rostrally and dorsally

- Soft palate pushed upwards to close nasopharynx

- Epiglottis tilts backwards, partially covering laryngeal entrance

- Arytenoid cartilages pull the vocal folds together

- Main seal is closure of the glottis

- Inhibition of respiration

- Food passes from oropharynx, to common pharynx, then into laryngopharynx and oesophagus

Describe the functions of the glottis.

- Closes during swallowing

- Sudden opening permits coughing

Describe the larynx structure in birds.

- Cricoid and arytenoid cartilages

- No vocal folds

- Glottis can be closed

- Syrinx at the tracheal bifurcation creates sound