16. Functional Anatomy of the Larynx Flashcards
What are 4 functions of the larynx?
- Airway protection: preventing food/fluid
etc entering airways - Ventilation (movement of air into/out of lungs)
- Important role in cough reflex: rapidly expel anything inadvertently entering airway
- Role in production of sound (phonation)
What is the larynx suspended from and by what?
Suspended from the hyoid bone, by the thyrohyoid membrane which attaches it to the thyroid cartilage
Where does the larynx start and end?
Begins at laryngeal inlet and ends at lower border of cricoid cartilage (C6)
What lies to posterior to the the larynx?
Laryngopharynx
What cartilages make up the larynx?
Epiglottis, thyroid, arytenoid and cricoid
cartilages
What joints are present between the cartilages of the larynx?
Synovial joints between:
- (inferior horn of) Thyroid and cricoid: cricothyroid
- arytenoids and cricoid: cricoarytenoid
What membranes contributes to the larynx?
- thyrohyoid membrane
- cricothyroid membrane (between 1st tracheal ring and cricoid)
- cricotracheal membrane
What are the attachments of the cricothyroid membrane?
Runs upwards from the cricoid cartilage, but deep to the thyroid cartilage giving a free upper margin that attaches anteriorly (to inner surface of thyroid cartilage) and posteriorly (to the arytenoid cartilages).
What forms the true vocal cords?
Thickening of the free upper margin of the Cricothyroid membrane, forming the vocal ligament
What forms the false vocal cords?
Free lower border of quadrangular membrane
What are the attachments of the quadrangular membrane?
runs from lateral edges of epiglottis to arytenoid cartilage
What emergency operation is done on the larynx?
Cricothyroidotomy
What is a cricothyrotomy?
Incision of the larynx through the cricothyroid membrane, accessing directly the infraglottis.
- temporary solution
On what occasion might a cricothyroidotomy be done?
On very rare occasions when a patient cannot be intubated or ventilated (e.g swelling to vocal cords)
access can be gained into airway via cricothyroid membrane
What are the attachments of the epiglottis?
- hyoid bone
- Anterior thyroid cartilage, inner surface (thyroglottic ligament)
- sides of the epiglottis are connected to the arytenoids by aryepiglottic folds
What connects the epiglottis to the arytenoids?
The aryepiglottic folds
What are the aryepiglottic folds?
Folds of mucous membranes formed at the superior margin of the quadrangular membrane.
What is the latyngeal inlet and what is formed by?
Opening (of the larynx)
- formed by epiglottis and the aryepiglottis fold
What is the term for adam’s apple?
laryngeal prominence
What is the only complete ring of cartilage in the respiratory tract?
Cricoid cartilage
Where do the arytendoids sit?
On top the the cricoid cartilage posteriorly, one on each side
What are the terms for true and false vocal cords/
True: vocal ligaments
Flase: vestiubular ligament
What forms the true and false vocal cords?
True: free upper border of the cricothyroid membrane
False: Free lower border of the quadrangular membrane
What is the difference in mobility of the false and true vocal cords?
False are fixed, true are mobile
What is the space between the true vocal cords called?
Rima glottidis
What are the different regions of the larynx?
- Supraglottis: up to and including false cords
- Glottis: between true vocal cords
- Infraglottis: between true vocal cords and first tracheal ring
What is between the vocal cords, what does this contain and what is the function?
Between vestibular and vocal folds is a small recess (ventricle) - Leads laterally and upwards into the saccule (or sinus); contains mucous glands that keep (true) vocal folds moist
Which part of the larynx is the narrowest?
glotttis
what is the supraglottis also called?
vestibule
What epithelial lines the larynx?
Pseudostratified ciliated columnar epithelium
- except the true vocal cords which are lines with Stratified squamous epithelium
Why are the vocal cords lined with stratified squamous epithelium?
to resist abrasive effect of air
What is the space between the epiglottis and the tongue called?
Valleculla
What is the clinical function of the valleculla?
it is where the tip of laryngoscope can be placed when intubating
What is intubation and what must be viewed during the process?
Vocal cords must be viewed for intubation: placement of an endotracheal tube into subglottic region (i.e. below vocal cords)
What is flexible nasoendoscopy?
Insert flexible endoscope via nasal cavity and pharynx to then visualise larynx
What are the 2 main actions of the intrinsic muscles of the larynx?
Alter the
- Size/shape of laryngeal inlet
- Tension/position of vocal cords
What happens to the vocal cords and laryngeal inlet during swallowing?
Close - to protect the respiratory tract
What happens to the vocal cords and latungeal inlet during inspiration and expiration?
- Open vocal cords (and laryngeal inlet)
- Allowing movement of air
What happens to the vocal cords in phonation?
partially closed vocal cords - slight gap to allow air to move through to vibrate
What happens to vocal cords during the cough reflex?
tightly closed (adducted) vocal cords rapidly snap open(abduct)
What helps close the laryngeal inlet when swallowing?
- Epiglottis moves down
- muscles in the aryepiglottic folds contract and constrict the laryngeal inlet
Of the many intrinsic muscles of the larynx, how many open the vocal cords?
1 - posterior crycoarytenoid (abducts the vocal cords)
- rotates the arytenoids outward
rest act to adduct the vocal cord
what structure are the muscles involved in opening and closing vocal cords associated with?
arytenoid cartilage
What are the attachments of the posterior crycoartyenoid cartilage?
runs from the cricoid cartilage to the arytenoid cartilage posteriorly
What are the attachments of the vocalis muscle?
anteriorly attached to inner surface of thyroid cartilage and posterior surface attached to arytenoid cartilage
- vocalis runs along the length of the true vocal cords
What determines the size of rima glottidis and how does this relate to function of laryngeal muscles?
Arytenoids position on cricoid determines position of true vocal cords and therefore size of aperture (rima glottidis/glottis)
- muscles act to change the position of the arytenoids
What are the intrinsic muscles of the larynx supplied by?
Recurrent laryngeal nerve of vagus (CN X)
- Except cricothyroid muscle (external branch of superior laryngeal nerve) - intrinsic muscle found outside cartilages
What is the position of the vocal cords in inspiration and expiration?
VC aBduct
What is the position of the vocal cords in phonation?
- VC closely aDduct
- slight gap to allow small air through
- Expired air forced through closely adducted vocal cords
How are sound waves created in phonation?
Due to vibration of the vocal cords
How do we cough?
- inspire and fill lungs with air
- vocal cords then aDducted
- expiratory muscles contract
- intrathoracic pressure builds
- then cords suddenly aBducted
- explosive outflow of air!
Where do the vocal cords need to meet for phonation and cough and what is indicated if they dont?
- Both vocal cords have to meet in midline (aDduct) to allow for phonation and cough
- If movement of one vocal cord impaired (e.g. injury to nerve supplying muscles involved in its movement) phonation and cough will be impaired
What determines the pitch of sound?
Determined by Vocal Cord Tension
- high pitch, VC are taut
- low pitch, less taut
Which muscles is responsible for determining how taut the vocal cords are?
• Bilateral contraction cricothyroid muscle ↑ tension in vocal cords
What is different about cricothyroid muscle compared to other intrinsic muscles of the larynx?
- Found on outside of larynx
- Innervated by external branch of superior laryngeal nerve (branch of CN X)
What is the action of the cricothyroid muscle?
Tilts Thyroid Cartilage forward on Cricoid Increasing Tension in Vocal Cords Important for Reaching Higher Pitch
What does injury to the superior laryngeal nerve lead to?
Loss of innervation to the cricothyroid muscle
- hoarseness of voice especially when attempting higher pitched sounds
surgery of what structure can lead to injury of the external branch of superior laryngeal nerve?
This nerve (closely related to superior thyroid artery) Can be injured in thyroid surgery
Describe the cricothyroid membrane and when it can be punctured?
Part of the cricothyroid membrane can be palpated anteriorly and, in acute laryngeal obstruction (e.g. due to laryngospasm, tongue swelling) can be punctured enabling a patient to breathe. Puncturing through the cricothyroid membrane allows rapid access into the infraglottic area of the larynx
describe the thyroid cartilage
The thyroid cartilage is shield-like, and made up of two lateral plates meeting in the midline as a prominent ‘V’ (‘Adam’s apple’) called the laryngeal prominence
Describe the cricoid cartilage
cricoid cartilage is signet-ring shaped and the only complete ring of cartilage throughout the respiratory tract. Inferiorly, it is attached to the trachea by the
cricotracheal membrane. The arytenoids sit on top of the cricoid cartilage posteriorly, one on each side.
Describe the use of laryngoscope in intubation
If a patient requires intubation (e.g. prior to surgery), an anaesthetist will view the larynx using a laryngoscope. The process of intubation requires a tube (endotracheal [ET] tube) to be passed through the patient’s oral cavity, oropharynx and then into the larynx and through the vocal cords, so that it sits in the upper part of the trachea.
The ET tube has a small balloon (cuff) at the end
that is inflated to ensure the tube remains securely in place. The ET tube has a lumen, which allows for mechanical ventilation and oxygenation of the patient’s lungs
What are the actions of the intrinsic muscles of larynx?
Act to move the arytenoid cartilage at the cricoarytenoid joint thus allowing opening and closing of the rima glottidis by abducting and adducting the true vocal cords - except circothyroid
What is the function of the suprahydoids and longitudinal pharyngeal muscles during swallowing?
Act to elevate and anteriorly displace the larynx
• Helps ensure patency of pharynx so food/fluid can be directed into it - longitudinal pharyngeal muscles elevate and expand pharynx to open it
What provides sensory innervation to the 3 different regions of the larynx?
Recurrent laryngeal: Subglottic region
Internal superior laryngeal: Supraglottic and glottic regions
What are the two divisions of the vagus nerve that innervate the larynx?
Superior Laryngeal
Recurrent Laryngeal
What are the 2 division of the superior laryngeal nerve?
- Internal (sensory to glottis and supraglottis)
- external (motor to cricothyroid)
Where does the internal superior laryngeal nerve enter the larynx?
Pierces through the thyrohyoid membrane
What artery is the external branch of the superior laryngeal nerve close to and what is the implication of this?
Superior thyroid artery
- may be damaged in surgery involving this artery
What does the recurrent laryngeal nerve innervate?
- Sensory to infraglottic (sensory of vocal cords and below vocal cords )
- Motor to all intrinsic muscles of larynx (except cricothyroid)
What is the course of the recurrent laryngeal nerves?
• Recurrent laryngeal nerve arises distally from vagus
• Passes anteriorly to then loops under right SCA and on left, the arch or aorta
• Ascends in tracheo-oxxxesophageal groove
• Close anatomical relationship with thyroid
gland and inferior thyroid arteries supplying the gland
What might cause damage/compression of the RLN?
Recurrent laryngeal nerves is close relation of inferior thyroid artery - Potentially injured during thyroid surgery
Other anatomical relations of RLN during its journey (on left and right side)
- Aortic arch aneurysm (left RLN)
- Cancer involving apex of lung (right RLN)
- Disease or surgery involving larynx, oesophagus or thyroid
What are the symptoms of
What are the symptoms of unilateral RLN lesions and why?
• RLN supplies intrinsic muscles of larynx responsible for vocal cord movements
• Unilateral RLN lesions lead to unilateral vocal cord palsies
– hoarse voice, ineffective cough
What position do paralysed vocal cords assume?
paramedian position
- Between fully abducted and fully adducted
Why might symptoms of a unilateral RLN palsy get better?
Often contralateral side compensates in time (crosses midline to meet vocal cord on affected side)
Why is bilateral RLN palsy more dangerous?
– Both vocal cords paralysed and in paramedian postion
– Narrow glottis
– Significant airway obstruction…emergency surgical airway
summarise how intrinsic muscles help direct food away from larynx during swallowing
number of the intrinsic muscles attach to the epiglottis, and their contraction pulls down on the sides of the epiglottis so that it covers over the laryngeal inlet. The action of these muscles and the contraction of the suprahyoid muscles and longitudinal pharyngeal muscles (which pull the larynx upwards, helping tilt the epiglottis further) ensure that the laryngeal inlet is safely covered by the epiglottis and that food /fluids are directed away from the laryngeal opening as we swallow, into the piriform fossae.
