10.1 Functional Anatomy Of The Larynx Flashcards
Where is the larynx located?
Between the hyoid bone (laryngeal inlet) and lower border of the cricoid cartilage
(vertebral level C4-C6)
What are the functions of the larynx?
Ventilation
Airway protection
Cough reflex
Production of sound (phonation)
How does the larynx protect the airway?
Prevents ingested food and liquid entering the lungs
What is the function of a cough?
important protective mechanism to expel rapidly any substances that have inadvertently found their way into the airways
What structures are involved with phonation?
Larynx Pharynx Oral cavity Lips Teeth Tongue
What are the subdivisions of the larynx?
Supraglottis
Glottis
Subglottis
What cartilages form the structural framework of the larynx?
Epiglottis
Thyroid cartilage
Arytenoid cartilage
Cricoid cartilage
What is the thyrohyoid membrane?
Membrane that attaches the thyroid cartilage (superior larynx) to the hyoid bone
Where does the cricothyroid membrane run?
Upwards from the cricoid cartilage, deep to the thyroid cartilage.
Attaches anteriorly to the inner surface of the thyroid cartilage
Attaches posteriorly to the arytenoid cartilages
What forms the vocal ligament?
The thickened upper margin of the cricothyroid membrane
What is the function of the vocal ligament?
To give shape and structure to the true vocal cord
What is laryngospasm?
Sudden spasm of the vocal cords
What is a cricothyroidotomy?
Puncturing the cricothyroid membrane anteriorly to allow rapid emergency access into the infraglottic area of the larynx, below the vocal chords . Provides a temporary solution in acute laryngeal obstruction, at or above the vocal chords.
What more definitive treatment can be given over a cricothyroidotomy?
A tracheotomy
What does the epiglottis attach to?
Hyoid
Back of the thyroid cartilage (thyroglottic ligament)
What is the epiglottis made out of?
Elastic cartilage
How does the the epiglottis attach to the arytenoid?
The aryepiglottic folds created by the upper border of the quadrangular membrane
What forms the aditus of the larynx?
The epiglottis and aryepiglottic folds
What is the laryngeal prominence?
The midline of the thyroid cartilage where the two lateral plates meet.
Describe the shape of the cricoid cartilage?
Signet ring shaped, only complete ring of cartilage throughout the respiratory tract
What is the function of the cricotracheal membrane?
To attach the cricoid cartilage to the trachea
Where are the arytenoids?
Sit on top of the cricoid cartilage, one on each side.
What structure sits behind the larynx?
The laryngopharynx
Where is the laryngeal inlet?
Opening from the laryngopharynx into the larynx. Found posteriorly and inferiorly to the posterior part of the tongue
What is the piriform fossa?
A recess on the posterolateral aspect of either side of the larynx
What is the function of the piriformis fossa?
Allows food/fluids to travel down into the oesophagus after being redirected away from the laryngeal inlet by the epiglottis.
What pathology can be involved with the piriformis fossa?
Sit for ingested food / foreign bodies to become lodged - choking
Pharyngeal cancers - can grow in recess to reasonable size before influencing swallowing
Describe the structure of the thyroid cartilage
Consists of 2 lateral lamina that fuse anteriorly to form a v shape. Extend superiorly to form superior horn and inferiorly to form the inferior horn in the midline
What are the synovial joint of the larynx?
Cricothyroid
Cricoarytenoid
How is the larynx suspended?
By the thyrohyoid membrane attaching to the hyoid bone
Where does the thyroid gland lie?
Below the cricoid cartilage.
Isthmus runs across the upper tracheal rings
What forms the false vocal cord?
The inferior border of the quadrangular membrane
What structure gives rise to the true vocal cord?
The superior free border of the cricothyroid membrane
Where is the supraglottis?
Laryngeal vestibule - From the upper border of the epiglottis / laryngeal inlet, down to include the false vocal cord/ inferior border of the quadrangular membrane
Where is the glottis?
From just below the false vocal cords to 1cm below the true vocal cords
Narrowest section of the larynx but includes the vocal cords
Where is the infralarynx/ subglottis?
From 1 cm below the true vocal cords to the inferior margin of the cricoid cartilage
What lines the larynx?
Mucous membrane
What is the saccule of the larynx?
A small lateral and upwards outpouching of mucous membrane between the false and true vocal cords. One on either side.
What is the function of the saccule of the larynx?
Contains mucous glands to keep the true vocal cords moist as the true vocal cords are not lined with mucus membrane
What type of epithelium lines the larynx?
Pseudostratified ciliated columnar epithelium with goblet cells
What epithelium lines the true vocal cords?
Stratified squamous epithelium
Why do the vocal cords have a different type of epithelium to the rest of the larynx?
Have stratified squamous epithelium - true vocal cords are very mobile and are subject to abrasion of air.
How is the larynx viewed clinically?
With a laryngoscope
Flexible nasoendoscopy
What is the rima glottidis?
The space between the 2 true vocal cords, varies in width during phonation.
What anatomical landmark can be used to orientate a laryngoscopic view of the larynx?
The point of the rima glottidis points anteriorly.
Why would be need to visualise the larynx laryngoscopically?
Intubation
To visualise the anatomy of larynx and pharynx if suspecting pathology
What is intubation?
placement of an endotracheal tube into subglottic region (i.e. below vocal cords)
What is the vallecula?
A small recess between the epiglottis and the posterior root of the tongue. Where the tip of laryngoscope can be placed when intubating
What is a flexible nasoendoscopy?
A flexible endoscope that is inserted via nasal cavity and pharynx to then visualise the larynx. Can be used on a conscious patient
What are the 2 main functions of intrinsic muscles of the larynx?
To change the size/shape of the laryngeal inlet
Tension/position of the vocal cords
How do the intrinsic muscles of the larynx function during swallowing?
Close the laryngeal inlet and vocal cords
Protect respiratory tract from ingested food/fluid
How do the intrinsic muscles of the larynx function during inspiration and expiration?
Open vocal cords and laryngeal inlet
Allow movement of air
How do the intrinsic muscles of the larynx act during phonation?
Partially adducted vocal cords
How do intrinsic muscles act during the cough reflex?
Closely adducted, closing the trachea whilst be build up intrathoracic pressure.
Snapped open during the cough to allow air to be rapidly expelled
How does the laryngeal inlet shut?
Epiglottis tips down
- passively as the tongue pushes back onto it a we swallow
- muscles in the aryepiglottic folds contract
Only one intrinsic muscle of the larynx acts to widen the rima glottidis/ adduct the vocal cords. Which is it?
Posterior cricoarytenoid
How do we alter the size of the rima glottidis?
By rotating the arytenoid cartilages on the cricoid
What innervates most of the instrinsic muscles of the larynx?
Recurrent laryngeal nerve of vagus (CN X)
1 on each side (right and left)
Which instrinsic muscle of the larynx is not innervated by the recurrent laryngeal nerve of vagus?
The cricothyroid muscle
What innervates the cricothyroid muscle?
External branch of the superior laryngeal nerve (CN X)
During phonation what happens to the vocal cords?
VC closely adducted.
Expired air is forced through closely adducted vocal cords
VC vibration creates sound waves
How do the vocal cords move in the cough reflex?
– inspire and fill lungs with air – vocal cords then aDducted – expiratory muscles contract – intrathoracic pressure builds – then cords suddenly aBducted – explosive outflow of air!
If the movement of one vocal cord is impaired, what will be effected?
Inability to met the other vocal cord in the midline
- impaired phonation
- impaired cough
How does tension of the vocal cords affect the pitch of phonation?
High pitched sounds = vocal cords are taut
Low pitched sounds = vocal cords less taut
How do we change the pitch of our voice?
By changing the tension of the vocal cords.
Varied by contraction of the cricothyroid muscle, contraction increases tension.
Where is the cricothyroid cartilage located?
On the outside of the larynx
Runs from the anterior of the cricoid cartilage onto the outer surface of the thyroid cartilage
What is the action of the cricothyroid muscle?
Tilts thyroid cartilage forwards on the cricoid cartilage. Increases tension in vocal cords allowing for higher pitch
What innervates the cricothyroid muscle?
External branch of the superior laryngeal nerve (CN X)
What structure is the external branch of the superior laryngeal nerve closely associated to?
Superior thyroid artery.
When might innervation to the cricothyroid muscle be reduced?
During thyroid surgery.
Superior thyroid artery lies very close to the external branch of the superior laryngeal nerve. Injury results in hoarseness of voice, especially when attempting higher pitched sounds
What part of the airway is shared by our respiratory and digestive system?
Oropharynx
Describe the movement of the larynx during swallowing.
Hyoid bone elevated and moved anteriorly by suprahyoid muscles
Larynx moves up and forward
Tongue pushes epiglottis posteriorly and aryepiglottic muscles contract
– Narrowing laryngeal inlet
– Bringing epiglottis from a vertical to a
more horizontal position
Closure (adduction) of vocal cords (closes glottis)
What is the role of the suprahyoids and longitudinal pharyngeal muscles during swallowing?
Suprahyoids = contract the anteriorly and superiorly displace hyoid and bone
Longitudinal pharyngeal muscles = contract to anteriorly displace larynx
Describe the sensory innervation of the larynx
Vagus nerve (CN X)
- Internal Superior laryngeal nerve - sensory supraglottis
- recurrent laryngeal nerve - sensory to the subglottis and glottis
Describe the motor innervation of the larynx
Vagus nerve (CN X)
- external superior laryngeal to the cricothyroid muscle
- recurrent laryngeal to the intrinsic muscles of the larynx
Describe the path of the superior laryngeal branch
CN X exits cranium via jugular foramen. Passes into the carotid sheath, travelling inferiorly.
Superior laryngeal branch arises in the neck.
Internal branch pierces through the thyrohyoid membrane to enter larynx.
External branch does not enter the larynx and innervates the cricothyroid muscle.
Describe the path of the recurrent laryngeal nerve to the larynx
Recurrent laryngeal nerves arise inferiorly and ascend to innervate intrinsic muscles of the larynx
right = arises in neck, hooks underneath right subclavian artery to ascend to larynx in a groove between the oesophagus and the trachea (trachealoesophagus groove)
Left = arises in the thorax. Hooks under the arch of the aorta. Ascends to larynx in the trachealoesophagus groove.
What structures have a close anatomical relationship with the recurrent laryngeal nerves?
Thyroid gland
Inferior thyroid arteries
When are the recurrent laryngeal nerves vulnerable to injury?
In thyroid surgery (close to inferior thyroid arteries)
Aortic arch aneurysm ( left RLN)
Cancer involving apex of the lung (right RLN)
Disease or surgery involving the larynx, oesophagus or thyroid
Describe the symptoms of unilateral recurrent laryngeal nerve lesion?
Unilateral vocal cord palsies
- hoarse voice, ineffective cough
Contralateral side compensates over time (crosses midline to meet vocal cord on affected side)
What is the position of a paralysed vocal cord?
Paramedian position - partially abducted/ adducted
How does a bilayer recurrent laryngeal nerve lesion present?
Both vocal cords paralysed and in paramedian position
Narrow glottis
Significant airway obstruction
How are bilateral recurrent laryngeal nerve palsies treated?
Emergency surgical airway - access below vocal cords.
