Difference between revisions of "Larynx - Anatomy & Physiology"

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<big><center>[[Anatomy & Physiology|'''BACK TO ANATOMY & PHYSIOLOGY''']]</center></big>
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<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>
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 +
 
 
==Introduction==
 
==Introduction==
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[[Image:Larynx Anatomy.jpg|thumb|right|250px|Anatomy of the Larynx - Copyright University of Nottingham]]
 
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[[Image: Annotated horse larynx.JPG|thumb|right|250px|Annotated horse larynx- Copyright RVC]]
 
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[[Image:Epiglottic cartilage.jpg|thumb|right|250px|Epiglottic Cartilage - Copyright RVC]]
 
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[[Image:Thyroid cartilage.jpg|thumb|right|250px|Thyroid Cartilage - Copyright nabrown RVC]]
 
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[[Image:Cricoid cartilage.jpg|thumb|right|250px|Cricoid Cartilage - Copyright nabrown RVC]]
 
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[[Image:Arytenoid cartilages.jpg|thumb|right|250px|Arytenoid Cartilages - Copyright nabrown RVC]]
 
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[[Image:Pharynx Anatomy.jpg|thumb|right|250px|Pharynx Labelled - Copyright C.Clarkson and T.F.Fletcher University of Minnesota]]
 
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[[Image:Epiglottis histology.jpg|right|thumb|250px|Epiglottis Histology - Copyright RVC]]
 
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[[Image:Epiglottis histology 2.jpg|right|thumb|250px|Epiglottis Histology - Copyright RVC]]
 
  
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The larynx is situated below where the [[Pharynx - Anatomy & Physiology|pharynx]] divides into the trachea and the [[Oesophagus - Anatomy & Physiology|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 larynx is situated below where the [[Pharynx - Anatomy & Physiology|pharynx]] divides into the trachea and the [[Oesophagus - Anatomy & Physiology|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.
  
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The cartilagenous larynx can be manually palpated in the living animal and is commonly implicated in respiratory conditions such as [[Laryngeal Paralysis|roaring]].
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The cartilageous larynx can be manually palpated in the living animal and is commonly implicated in respiratory conditions such as [[Diseases of the conducting airways#Laryngeal paralysis|roaring]].
  
 
==Structure==
 
==Structure==
  
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The [[Pharynx - Anatomy & Physiology|pharynx]] is located rostrally to the larynx, whilst the trachea is located caudally. The larynx is suspended from the [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]. It is bilaterally symmetrical and 'tube-shaped' and can be described as a '''musculocartilagenous organ'''.
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*[[Pharynx - Anatomy & Physiology|Pharynx]] rostrally
 +
 
 +
*Trachea caudally
  
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The larynx moves position when the animal [[Deglutition|swallows]] due to its attachments to the [[Tongue - Anatomy & Physiology|tongue]] and the '''basihyoid bone''' of the [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]] by the '''thyrohyoid membrane'''.
+
*Suspended from the [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]
  
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===Synovial joints===
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*Moves position when the animal [[Deglutition|swallows]] due to its attachments to the [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] and the [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]
  
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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.
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*Synovial joints  
 +
**Between the thyrohyoid bone and the dorsorostral aspect of the thyroid cartilage
 +
**Dorsal joint of throid cartilage
 +
**Lateral aspect of cricoid cartilage and dorsocaudal aspect of throid cartilage
  
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===Ligaments===
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*Movement of the cricoid-arytenoid joint controls the size of the glottic opening, lumen and larynx
  
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Membranes and elastic ligaments attach the laryngeal cartilages, allowing attachment of the epiglottis to the '''thyroid''' and '''cricoid cartilage'''. The first tracheal ring has attachment with the '''cricoid cartilage''' by the '''cricotracheal ligament'''.
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*Membranes and elastic ligaments attach the laryngeal cartilages
 +
**[[Epiglottis]] to throid and cricoid cartilage
 +
**First tracheal ring with cricoid cartilage
  
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===Extrinsic musculature===
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*Vocal folds and vestibular folds
 +
**Made of (slightly stiffer) elastic ligaments
 +
**Pass between the arytenoid cartilages and the laryngeal floor
  
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Extrinsic musculature connects the larynx to the sternum, [[Tongue - Anatomy & Physiology|tongue]], [[Pharynx - Anatomy & Physiology|pharynx]] and [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]].
+
*Extrinsic musculature connects the larynx to the sternum, [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]], [[Pharynx - Anatomy & Physiology|pharynx]] and [[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]
  
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===Intrinsic musculature===
+
*Intrinsic musculature connects the laryngeal cartilages (see [[Larynx - Anatomy & Physiology#Intrinsic Musculature|here]])
 +
**All skeletal muscles
  
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Intrinsic musculature connects the laryngeal cartilages (see below).
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*The vestibule extends from the entrance of the larynx to the arytenoid cartilages and vocal folds
 +
**Vestibular folds run parallel, but rostral to, the vocal folds
  
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===Vestibule===
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*The glottic cleft (rima glottidis) is surrounded by the arytenoid cartilages dorsally and vocal folds ventrolaterally
 +
**Varies in size
 +
**Diamond shaped
 +
**Glottic cleft disappears when the glottis is closed
 +
**Vocal folds run caudodorsally
  
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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'''.
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*The infraglottic cavity extends from the caudal section of the arytenoid cartilages into the lumen of the trachea
 +
**Fixed size
  
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===Glottic cleft===
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*[[Epiglottis]] is the rostral margin of the larynx
  
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The '''glottic cleft''' (rima glottidis) is surrounded by the '''arytenoid cartilages''' dorsally and '''vocal cords''' 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.
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===Thyroid Cartilage===
  
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===Epiglottis===
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*[[Bones and Cartilage - Anatomy & Physiology#Hyaline Cartilage|Hyaline cartilage]]
 +
 +
*Forms most of the floor of the larynx
  
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The epiglottis is the rostral margin of the larynx. It is a flap of [[Cartilage - Anatomy & Physiology#Elastic Cartilage|elastic cartilage]] covered by mucous membrane. It forms the rostral boundary of the larynx and prevents food particles from entering the trachea. The epiglottis can return to its normal size and shape after distortion due to the vast amount of elastic fibres present within.
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*Fusion of the two lateral plates varies in different species
  
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Avian species do not have epiglottis.
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*Rostral part forms the 'Adam's apple'
  
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==The Cartilage of the Larynx==
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*Articulates with the thyrohyoid bone
  
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===Thyroid Cartilage===
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*Articulates with the cricoid cartilage
  
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The thyroid cartilage is a [[Cartilage - Anatomy & Physiology#Hyaline Cartilage|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 thyroid cartilage articulates with the '''thyrohyoid bone''' and the '''cricoid cartilage'''. It becomes brittle as the animal ages.
+
*Becomes brittle as the animal ages
  
 
===Cricoid Cartilage===
 
===Cricoid Cartilage===
  
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The cricoid cartilage is also a [[Cartilage - Anatomy & Physiology#Hyaline Cartilage|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 edge. The cricoid cartilage articulates with the '''thyroid cartilage'''. It also becomes brittle as the animal ages.
+
*[[Bones and Cartilage - Anatomy & Physiology#Hyaline Cartilage|Hyaline cartilage]]
 +
 
 +
*Signet ring shape
 +
**Wider on dorsal surface
 +
**Narrower on ventral surface
 +
 
 +
*Crest on midline of dorsal surface
 +
 
 +
*Facets for arytenoid cartilages on rostral egde
 +
 
 +
*Articulates with the thyroid cartilage
 +
 
 +
*Becomes brittle as the animal ages
  
 
===Arytenoid Cartilage===
 
===Arytenoid Cartilage===
  
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The arytenoid cartilage is also a [[Cartilage - Anatomy & Physiology#Hyaline Cartilage|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.
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*[[Bones and Cartilage - Anatomy & Physiology#Hyaline Cartilage|Hyaline cartilage]]
 +
 
 +
*Paired
 +
 
 +
*Articulates with the rostral part of the cricoid cartilage
 +
 
 +
*Vocal process present on caudal surface where the vocal folds attach
 +
**Muscular process extending laterally
 +
**Corniculate process extending dorsomedially (elastic cartilage)
  
 
===Epiglottic Cartilage===
 
===Epiglottic Cartilage===
  
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The epiglottic cartilage is an [[Cartilage - Anatomy & Physiology#Elastic Cartilage|elastic cartilage]], which is the most flexible and most rostral type of cartilage. The thinner stalk-like part, is attached to the root of the [[Tongue - Anatomy & Physiology|tongue]], the 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|deglutition]], the large blade part of the '''epiglottic cartilage''' partially covers the entrance to the trachea.
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*[[Bones and Cartilage - Anatomy & Physiology#Elastic Cartilage|Elastic cartilage]]
 +
 
 +
*Flexible
 +
 
 +
*Most rostral
 +
 
 +
*Thinner stalk-like part is attached to the root of the [[Oral Cavity - Tongue - Anatomy & Physiology|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|deglutition]] the large blade part of the epiglottic cartilage partially covers the entrance to the trachea
  
 
===Interarytenoid Cartilage===
 
===Interarytenoid Cartilage===
  
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The interarytenoid cartilage is a nodule of [[Cartilage - Anatomy & Physiology#Hyaline Cartilage|hyaline cartilage]]. It is located between the '''arytenoid cartilages''' dorsally.
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*Nodule of [[Bones and Cartilage - Anatomy & Physiology#Hyaline Cartilage|hyaline cartilage]]
 +
 
 +
*Between arytenoid cartilages dorsally
  
 
===Cuneiform Process===
 
===Cuneiform Process===
  
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The cuneiform process is formed by [[Cartilage - Anatomy & Physiology#Elastic Cartilage|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'''.
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*[[Bones and Cartilage - Anatomy & Physiology#Elastic Cartilage|Elastic cartilage]]
 +
 
 +
*Supports mucosal folds from [[Epiglottis|epiglottis]] to arytenoid cartilages
 +
 
 +
*Not present in all species
  
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==The Vocal and Vestibular Folds==
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*Free or fused with the epiglottic cartilages and arytenoid cartilages depending on species
  
 
===Vocal Folds===
 
===Vocal Folds===
−
+
 
−
The vocal folds are made of (slightly stiffer) elastic ligaments and pass between the '''arytenoid cartilages''' and the '''laryngeal floor'''. They run caudodorsally, with the ligament positioned medially and the '''vocalis muscle''' laterally. Fat surrounds the vocalis muscle. The vocal folds form part of the glottis and secrete mucous. They are used for vocalisation.
+
*Rostral part of laryngeal floor to arytenoid cartilages
 +
 
 +
*Run caudodorsally
 +
 
 +
*Ligament medially
 +
 
 +
*Vocalis muscle laterally
 +
 
 +
*Fat surrounds vocalis muscle
 +
 
 +
*Form part of the glottis
 +
 
 +
*Secrete mucous
 +
 
 +
*Vocalisation
  
 
===Vestibular folds===
 
===Vestibular folds===
−
+
 
−
The vestibular folds are made of (slightly stiffer) elastic ligaments. The '''vestibular ligaments''' are rostral to the '''vocal ligament'''. The vestibular folds run caudodorsally, rostral to the vocal folds with the ligament positioned medially and the '''vocalis muscle''' laterally.
+
*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==
 
==Intrinsic Musculature==
  
−
===Cricothyroid muscle===
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===Cricothryroid muscle===
−
The cricothyroid muscle is innervated by the '''cranial laryngeal nerve''', a branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]). It moves the '''cricoid''' and '''arytenoid''' cartilages caudally to tense the vocal folds.
+
*Innervated by the cranial laryngeal nerve a branch of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
 +
*Moves cricoid and arytenoid cartilages caudally
 +
*Tenses vocal folds
  
 
===Dorsal cricoarytenoid muscle===
 
===Dorsal cricoarytenoid muscle===
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The dorsal cricoarytenoid muscle is innervated by the '''caudal laryngeal nerve''', a branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]). It runs from the dorsal surface of the '''cricoid cartilage''' to the '''arytenoid cartilage'''. It abducts the vocal process and therefore the vocal fold to widen the glottis.
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*Innervated by the caudal laryngeal nerve a branch of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
 +
*Dorsal surface of cricoid cartilage to arytenoid cartilage
 +
*Abducts vocal process and therefore vocal fold
 +
*Widens glottis
  
 
===Lateral cricoarytenoid muscle===
 
===Lateral cricoarytenoid muscle===
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The lateral cricoarytenoid muscle is innervated by the '''caudal laryngeal nerve''', a branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]). It adducts the vocal processes and narrows the glottis.
+
*Innervated by the caudal laryngeal nerve a branch of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
 +
*Adducts vocal processes
 +
*Narrows the glottis
  
 
===Thyroarytenoid muscle===
 
===Thyroarytenoid muscle===
−
The thyroarytenoid muscle is innervated by the '''caudal laryngeal nerve''', a branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]). It runs from the laryngeal floor to the '''thyroid cartilage''' and '''arytenoid cartilage''' and alters the tension of the vocal and vestibular folds. It forms part of the '''sphincter muscular arrangement'''.
+
*Innervated by the caudal laryngeal nerve a branch of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|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===
 
===Transverse arytenoid muscle===
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The transverse arytenoid muscle is innervated by the '''caudal laryngeal nerve''', a branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]). It completes the '''muscular sphincter arrangment''' and spans the '''arytenoid cartilages'''.
+
*Innervated by the caudal laryngeal nerve a branch of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
 +
*Completes the muscular sphincter arrangment
 +
*Spans the arytenoid cartilages
  
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==Laryngeal Pharynx==
 
  
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The laryngeal pharynx is the largest part of the [[Pharynx - Anatomy & Physiology|pharynx]]. It is wide rostrally and narrows caudally. The laryngeal pharynx joins the [[Oesophagus - Anatomy & Physiology|oesophagus]] at the mucosal folds (clearest in the canine, in other species it is harder to see the demarcation). The lumen is 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==
  
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==Function==
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*[[Deglutition|Swallowing]]
  
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The larynx protects the trachea in [[Deglutition|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 - Anatomy & Physiology|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.
+
*Communication
  
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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.
+
*Passage of air to the lungs
  
 
==Vasculature==
 
==Vasculature==
  
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'''Laryngeal branch of the superior thyroid artery''' supplies the rostral larynx and is a branch of the '''carotid artery'''.
+
*Laryngeal branch of superior thyroid artery
 +
**Supplies rostral larynx
 +
**Branch from carotid artery
  
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'''Laryngeal branch of inferior thyroid artery''' supplies the caudal larynx and is branching from the '''subclavian artery''' from the '''thyrocervical trunk'''.
+
*Laryngeal branch of inferior thyroid artery
 +
**Supplies caudal larynx
 +
**Branch from subclavian artery from thyrocervical trunk
  
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'''Laryngeal branch of cricothyroid artery''' branches from the '''superior thyroid artery'''.
+
*Laryngeal branch of cricothyroid artery
 +
**Branch from superior thyroid artery
  
 
==Innervation==
 
==Innervation==
  
−
The larynx is innervated by branches of the '''vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]).
+
*Branches of the vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
 +
**Cranial larygeal nerve
 +
**Caudal (recurrent) laryngeal nerve
  
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'''Cranial laryngeal nerve''' has two branches. The internal branch innervates the mucosa and the external branch innervates the '''cricothyroid muscle''' and constricts the [[Pharynx - Anatomy & Physiology|pharynx]].
+
==Lymphatics==
  
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'''Caudal (recurrent) laryngeal nerve''' innervates the intrinsic muscles of the larynx (except the cricothyroid muscle).
+
*Lymphoid tissue present
  
−
==Lymphatics==
+
==Histology==
  
−
Lymphoid tissue is present.
+
*Mucous glands present  
  
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==[[Species Differences in Laryngeal Structure|Species Differences]]==
+
*In the ventricles, there is a high density of mucous glands
  
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The variation of the larynx between species is significant. More information can be found by clicking [[Species Differences in Laryngeal Structure|here]].
+
*Stratified squamous epithelium rostrally around laryngeal entrance
  
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==Histology==
+
*Ciliated pseudostratified columnar epithelium elsewhere
  
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Mucous glands are present in the larynx with a particularly high density in the ventricles. '''Stratified squamous epithelium''' is located rostrally around the laryngeal entrance, whilst '''ciliated pseudostratified columnar epithelium''' is elsewhere.
+
==Species Differences==
  
−
The epiglottis is covered by mucous membrane and contains irregular elastic fibres. They form a dense network of branching fibres around the chondrocytes and less dense branching fibres towards the perichondrium.
+
===Equine===
 +
*Fusion of the two plates of the thyroid cartilage is least extensive forming a rostral pointing notch which is a good site for surgical entry into the larynx
  
−
See [[Cartilage - Anatomy & Physiology#Elastic Cartilage|elastic cartilage histology]] for more information.
+
*Thyroarytenoid muscle is divided into 2 parts- rostral and caudal vocalis which are situated within the vocal folds and vestibular folds
  
−
See [[Cartilage - Anatomy & Physiology#Hyaline Cartilage|hyaline cartilage histology]] for more information.
+
===Canine===
 +
*Thyroarytenoid muscle is divided into 2 parts- rostral and caudal vocalis which are situated within the vocal folds and vestibular folds
  
 
==Links==
 
==Links==
  
−
[[:Category:Larynx - Pathology|Pathology of the Larynx]]
+
[[Larynx|Pathology of the Larynx]]
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[[Cartilage - Anatomy & Physiology|Cartilage - Anatomy & Physiology]]
 
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[[Aspiration Pneumonia|Aspiration Pneumonia]]
 
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{{Template:Learning
 
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|flashcards = [[Facial_Muscles_-_Musculoskeletal_-_Flashcards|Facial Muscles]]<br>[[Pharynx_-_Musculoskeletal_-_Flashcards#The_Laryngeal_Pharynx_Flashcards|Larynx and Pharynx]]<br>[[Larynx_-_Musculoskeletal_-_Flashcards|Larynx]]
 
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|powerpoints = [[Bone and Cartilage Histology resource|Interactive tutorial on bone and cartilage histology, including the Larynx]]
 
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|videos = [http://stream2.rvc.ac.uk/Anatomy/canine/head_neck/Pot0258.mp4 Lateral section through the head of a dog]
 
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|dragster = [[Canine Larynx Dissection Anatomy Resource]]<br>[[Canine Larynx Radiographical Anatomy Resource]]
 
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|OVAM = [http://www.onlineveterinaryanatomy.net/sites/default/files/original_media/document/asset_9291_Dog%20and%20horse%20larynges%20PDF.pdf Comparative Larynges 1]<br>[http://www.onlineveterinaryanatomy.net/sites/default/files/original_media/document/asset_9289_Comparative%20larynges%20PDF.pdf Comparative Larynges 2]<br>[http://www.onlineveterinaryanatomy.net/content/dog-larynx-dorsal-view Canine Larynx - Dorsal View]
 
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}}
 
  
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{{review}}
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[[Bones and Cartilage - Anatomy & Physiology|Cartilage - Anatomy & Physiology]]
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==Webinars==
 
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<rss max="10" highlight="none">https://www.thewebinarvet.com/respiratory/webinars/feed</rss>
 
  
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[[Category:Respiratory System - Anatomy & Physiology]][[Category:Musculoskeletal System - Anatomy & Physiology]]
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<big><center>[[Anatomy & Physiology|'''BACK TO ANATOMY & PHYSIOLOGY''']]</center></big>
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[[Category:A&P Done]]
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<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>

Revision as of 09:09, 29 July 2008

BACK TO ANATOMY & PHYSIOLOGY
BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY


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

  • Trachea caudally
  • Synovial joints
    • Between the thyrohyoid bone and the dorsorostral aspect of the thyroid cartilage
    • Dorsal joint of throid cartilage
    • Lateral aspect of cricoid cartilage and dorsocaudal aspect of throid cartilage
  • Movement of the cricoid-arytenoid joint controls the size of the glottic opening, lumen and larynx
  • Membranes and elastic ligaments attach the laryngeal cartilages
    • Epiglottis to throid and cricoid cartilage
    • First tracheal ring with cricoid cartilage
  • Vocal folds and vestibular folds
    • Made of (slightly stiffer) elastic ligaments
    • Pass between the arytenoid cartilages and the laryngeal floor
  • Intrinsic musculature connects the laryngeal cartilages (see here)
    • All skeletal muscles
  • The vestibule extends from the entrance of the larynx to the arytenoid cartilages and vocal folds
    • Vestibular folds run parallel, but rostral to, the vocal folds
  • The glottic cleft (rima glottidis) is surrounded by the arytenoid cartilages dorsally and vocal folds ventrolaterally
    • Varies in size
    • Diamond shaped
    • 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
    • Fixed size

Thyroid Cartilage

  • 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
  • Articulates with the cricoid cartilage
  • Becomes brittle as the animal ages

Cricoid Cartilage

  • Signet ring shape
    • Wider on dorsal surface
    • Narrower on ventral surface
  • Crest on midline of dorsal surface
  • Facets for arytenoid cartilages on rostral egde
  • Articulates with the thyroid cartilage
  • Becomes brittle as the animal ages

Arytenoid Cartilage

  • Paired
  • Articulates with the rostral part of the cricoid cartilage
  • Vocal process present on caudal surface where the vocal folds attach
    • Muscular process extending laterally
    • Corniculate process extending dorsomedially (elastic cartilage)

Epiglottic Cartilage

  • Flexible
  • Most rostral
  • 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

  • Between arytenoid cartilages dorsally

Cuneiform Process

  • Supports mucosal folds from epiglottis to arytenoid cartilages
  • Not present in all species
  • Free or fused with the epiglottic cartilages and arytenoid cartilages depending on species

Vocal Folds

  • Rostral part of laryngeal floor to arytenoid cartilages
  • Run caudodorsally
  • Ligament medially
  • Vocalis muscle laterally
  • Fat surrounds vocalis muscle
  • Form part of the glottis
  • Secrete mucous
  • Vocalisation

Vestibular folds

  • 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


Function

  • Communication
  • Passage of air to the lungs

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
    • Caudal (recurrent) laryngeal nerve

Lymphatics

  • Lymphoid tissue present

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

Species Differences

Equine

  • Fusion of the two plates of the thyroid cartilage is least extensive forming a rostral pointing notch which is a good site for surgical entry into the larynx
  • Thyroarytenoid muscle is divided into 2 parts- rostral and caudal vocalis which are situated within the vocal folds and vestibular folds

Canine

  • Thyroarytenoid muscle is divided into 2 parts- rostral and caudal vocalis which are situated within the vocal folds and vestibular folds

Links

Pathology of the Larynx

Cartilage - Anatomy & Physiology

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