Difference between revisions of "Larynx - Anatomy & Physiology"
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===Cuneiform Process=== | ===Cuneiform Process=== | ||
| − | + | The cuneiform process is [[Bones and Cartilage - Anatomy & Physiology#Elastic Cartilage|elastic cartilage]]. It supports '''mucosal folds''' from the [[Epiglottis|epiglottis]] to the '''arytenoid cartilages'''. It is not present in all species and can be free or fused with the '''epiglottic cartilages'''. | |
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==The Vocal and Vestibular Folds== | ==The Vocal and Vestibular Folds== | ||
Revision as of 20:53, 22 December 2010
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Introduction
The larynx is situated below where the pharynx divides into the trachea and the oesophagus. It is contained partly within the rami of the mandible and extends caudally into the neck. Vocal folds and vestibular folds are present in the larynx and due to this, it is more commonly known as the voice box.
The cartilageous larynx can be manually palpated in the living animal and is commonly implicated in respiratory conditions such as roaring.
Structure
The pharynx is located rostrally to the larynx, whilst the trachea is located caudally. The larynx is suspended from the hyoid apparatus. The larynx is bilaterally symmetrical and 'tube-shaped', it can be described as a musculocartilagenous organ.
The larynx moves position when the animal swallows due to its attachments to the tongue and the basihyoid bone of the hyoid apparatus by the thyrohyoid membrane.
Synovial joints
Synovial joints can be found between the thyrohyoid bone and the dorsorostral aspect of the thyroid cartilage. Synovial joints include the dorsal joint of thyroid cartilage; between the lateral aspect of the cricoid cartilage and the dorsocaudal aspect of the thyroid cartilage and between the cricoid and arytenoid cartilage. This allows abduction and adduction of the arytenoid cartilages. Movement of the cricoid-arytenoid joint controls the size of the glottic opening, the lumen and the larynx.
Ligaments
Membranes and elastic ligaments attach the laryngeal cartilages, allowing attatchment of the Epiglottis to the thyroid and cricoid cartilage. The first tracheal ring has attatchment with the cricoid cartilage by the cricotracheal ligament.
Extrinsic musculature
Extrinsic musculature connects the larynx to the sternum, tongue, pharynx and hyoid apparatus.
Intrinsic musculature
Intrinsic musculature connects the laryngeal cartilages (see here).
Vestibule
The vestibule extends from the entrance of the larynx to the arytenoid cartilages and vocal folds. The vestibular folds run parallel, but rostral to, the vocal folds.
Glottic cleft
The glottic cleft (rima glottidis) is surrounded by the arytenoid cartilages dorsally and vocal folds ventrolaterally. It varies in size and is diamond shaped. The glottic cleft disappears when the glottis is closed. Vocal folds run caudodorsally. The infraglottic cavity extends from the caudal section of the arytenoid cartilages into the lumen of the trachea. It is fixed in size.
Epiglottis
The Epiglottis is the rostral margin of the larynx.
The Cartilage of the Larynx
Thyroid Cartilage
The thyroid cartilage is hyaline cartilage and forms most of the floor of the larynx. The fusion of the two lateral plates varies in different species. The rostral part forms the 'Adam's apple'. The thyriod cartilage articulates with the thyrohyoid bone and the cricoid cartilage. It becomes brittle as the animal ages.
Cricoid Cartilage
The cricoid cartilage is also hyaline cartilage. It is 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 egde. The cricoid cartilage articulates with the thyroid cartilage. It also becomes brittle as the animal ages.
Arytenoid Cartilage
The arytenoid cartilage is also hyaline cartilage. It is 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. (elastic cartilage)
Epiglottic Cartilage
The epiglottic cartilage is elastic cartilage. It is flexible and the most rostral type of cartilage. The thinner stalk-like part is attached to the root of the tongue, body of the thyroid cartilage and the basihyoid bone. The larger blade-like part lies behind the soft palate and points dorso-rostrally. During deglutition, the large blade part of the epiglottic cartilage partially covers the entrance to the trachea.
Interarytenoid Cartilage
- Nodule of hyaline cartilage
- Between arytenoid cartilages dorsally
Cuneiform Process
The cuneiform process is elastic cartilage. It supports mucosal folds from the epiglottis to the arytenoid cartilages. It is not present in all species and can be free or fused with the epiglottic cartilages.
The Vocal and Vestibular Folds
Vocal Folds
- Made of (slightly stiffer) elastic ligaments
- Pass between the arytenoid cartilages and the laryngeal floor
- Run caudodorsally
- Ligament medially
- Vocalis muscle laterally
- Fat surrounds vocalis muscle
- Form part of the glottis
- Secrete mucous
- Vocalisation
Vestibular folds
- Made of (slightly stiffer) elastic ligaments
- Vestibular ligaments rostral to vocal ligament
- Rostral part of laryngeal floor to arytenoid cartilages
- Run caudodorsally, rostral to vocal folds
- Ligament medially
- Vocalis muscle laterally
- Fat surrounds vocalis muscle
- Do not form the glottis
Intrinsic Musculature
Cricothryroid muscle
- Innervated by the cranial laryngeal nerve a branch of the vagus nerve (CN X)
- Moves cricoid and arytenoid cartilages caudally
- Tenses vocal folds
Dorsal cricoarytenoid muscle
- Innervated by the caudal laryngeal nerve a branch of the vagus nerve (CN X)
- Dorsal surface of cricoid cartilage to arytenoid cartilage
- Abducts vocal process and therefore vocal fold
- Widens glottis
Lateral cricoarytenoid muscle
- Innervated by the caudal laryngeal nerve a branch of the vagus nerve (CN X)
- Adducts vocal processes
- Narrows the glottis
Thyroarytenoid muscle
- Innervated by the caudal laryngeal nerve a branch of the vagus nerve (CN X)
- Laryngeal floor to the thyroid cartilage and arytenoid cartilage
- Alters the tension of the vocal and vestibular folds
- Forms part of the sphincter muscular arrangement
Transverse arytenoid muscle
- Innervated by the caudal laryngeal nerve a branch of the vagus nerve (CN X)
- Completes the muscular sphincter arrangment
- Spans the arytenoid cartilages
Laryngeal Pharynx
- Largest part of the pharynx
- Wide rostrally
- Narrows caudally
- Joins oesophagus at mucosal folds (clearest in the canine, but in other species it is harder to see the demarcation)
- Lumen closed at rest by the roof and walls falling towards the floor
- The floor of the laryngeal pharynx contains the opening into the larynx- epiglottis, arytenoid cartilages and the aryepiglottic folds
Function
- 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
- Relfex stimulation of the mucosa promotes the coughing reflex
- Communication
- Passage of air to the lungs
- Increases intra-abdominal pressure
- Vocalisation
- The glottis can widen by adduction of the vocal folds when breathing is vigorous
Vasculature
- Laryngeal branch of superior thyroid artery
- Supplies rostral larynx
- Branch from carotid artery
- Laryngeal branch of inferior thyroid artery
- Supplies caudal larynx
- Branch from subclavian artery from thyrocervical trunk
- Laryngeal branch of cricothyroid artery
- Branch from superior thyroid artery
Innervation
- Branches of the vagus nerve (CN X)
- Cranial larygeal nerve
- Internal branch innervates mucosa
- External branch innervates cricothyroid muscle and constrictors of pharynx
- Caudal (recurrent) laryngeal nerve
- Innervates intrinsic muscles of larynx (except cricothyroid muscle)
- Cranial larygeal nerve
Lymphatics
- Lymphoid tissue present
Species Differences
The variation between the species is significant and is dealt with here
Histology
- Mucous glands present
- In the ventricles, there is a high density of mucous glands
- Stratified squamous epithelium rostrally around laryngeal entrance
- Ciliated pseudostratified columnar epithelium elsewhere
Test yourself with the Facial Muscles & Larynx/Pharynx Flashcards
Links
Cartilage - Anatomy & Physiology
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