L23: Functional anatomy of the larynx

Question 1

What sits directly behind the larynx?

Answer 1

Laringopharynx

Question 2

Where is the shared pathway for air and food?

Answer 2

Oropharynx, but air and food need to be directed down different tubes

Question 3

What are the functions of the larynx?

Answer 3

• airway protection (prevents food/fluid entering airways)
• ventilation
• important role in the cough reflex
• role in production of sound (phonation)

Question 4

What is the larynx?

Answer 4

‘Tube’ created by ligaments, membranes, cartilages, and muscles

• suspended from and lies below the hyoid bone
• begins at laryngeal inlet (an opening into larynx from laryngopharynx) and ends at lower border of the cricoid cartilage (C6): where the trachea begins

Question 5

What is the piriform fossa?

Answer 5

Space posterolaterally either side of the laryngeal inlet
-epiglottis directs food/fluid over and round through the piriform fossa, away from laryngeal inlet
(here can be a site where foods can get stuck/ pharyngeal cancers can grow to a resonable size before patient notes difficulties swallowing)

Question 6

What is the framework of the larynx?

Answer 6

Cartilaginous structures:
-thyroid cartilage on top
Inferior horn of the thyroid cartilage articulates with the cricoid cartilage below it (synovial joint)
The cricoid is thicker posteriorly
-arytenoid cartilages sit on top of the cricoid cartilage too (paired)
-epiglottis is attached to inner surface of the thyroid cartilage at the front

Membranes (connective tissue sheet)

• thyrohyoid membrane: attaches thyroid cartilage to the hyoid bone (suspends larynx)
• cricothyroid membrane: anteriorly connects the thyroid and cricoid cartilage (extends behind the anterior part of the thyroid cartilage)
• cricotracheal membrane: connecting cricoid cartilage to first tracheal ring

Question 7

What cartilages/membranes are palpable in the larynx?

Answer 7

-laryngeal prominence: thyroid cartialge (Adam’s apple)
Soft part after this is the cricothyroid membrane
-cricoid cartilage under this is palpable

Question 8

Where is the thyroid gland found?

Answer 8

Beneath the level of the cricoid cartilage, with the isthmus running across upper few tracheal rings

Question 9

What is a cricoidthyroidotomy?

Answer 9

Provides emergency acess to airway, below the level of the vocal cords (when there is an obstruction above this)
-hole cut in cricothyroid membrane in which a tube is then entered to oxygenate the patient

Question 10

What is the structure of the laryngeal inlet?

Answer 10

• epiglottis

- fold running down laterally from the edges of the epiglottis called: aryepiglottic folds

Question 11

What are the aryepiglottic folds formed from?

Answer 11

Quadrangular membrane (quadralateral in shape)
-runs from lateral edges of the epiglottis to the arytenoid cartilages
-free inferior border from middle of inner surface of the thyroid cartilage towards the arytenoid cartilage posteriorly
(free inferior boundary gives rise to the false vocal cord)

Question 12

What gives rise to the true vocal cord?

Answer 12

Free superior margin of the cricothyroid membrane

Question 13

What are the key regions of the larynx internally?

Answer 13

Supraglottis (also called the vestibule): from laryngeal inlet to the false vocal cord
Glottis: from true vocal cords to 1cm below them (narrowest part of the larynx)
Infraglottis: below the glottis until it turns into the trachea

Question 14

What is the larynx lined with?

Answer 14

Mucous membrane: pseudostratified ciliated columnae epithelium containing goblet cells
-there is a lateral and upwards outpouching of the mucous membrane between the false and true vocal cords: saccule of the larynx
(true vocal cords are lined with a different type of epithelium: stratified squamous epithelium)

Question 15

What is the function of the saccule of the larynx?

Answer 15

Contains mucous glands which keep true vocal cords moist

Question 16

What is the space between the true vocal cords?

Answer 16

Rima glottidis

Question 17

What is the vallecula?

Answer 17

Recess between posterior part of epiglottis and the root of the tongue
-where they place the tip of the laryngoscope during intubation

Question 18

What is a flexible nasoendoscopy?

Answer 18

Insertion of a flexible endoscope via nasal cavity and pharynx to then visualise the larynx

Question 19

What are the main actions of the intrinsic muscles of the larynx?

Answer 19

To:

• alter the size/shape of the laryngeal inlet
• alter the tension/position of vocal cords

Question 20

What happens to the larynx upon swallowing?

Answer 20

• close laryngeal inlet and vocal cords

- protection of the respiratory tract

Question 21

What happens to the larynx upon inspiration/expiration?

Answer 21

• open vocal cords ands laryngeal inlet

- allowing movement of air

Question 22

What happens to the larynx upon phonation/cough reflex?

Answer 22

Phonation: cords are partially closed, as there needs to be a small gap to allow air to pass through and be vibrated
Cough reflex: cords very adducted close together, and then rapidly abducted position where they snap open

Question 23

What muscles mainly move the true vocal cords?

Answer 23

Muscles around the arytenoid cartilages move the vocal cords outwards and inwards causing a narrowing of the rima glottidis
e.g. posterior cricoarytenoid (runs from back of cricoid cartilage and inserts onto the arytenoid cartilage)

-some muscles run along the length of the true vocal cords (vocalis muscle)

Question 24

What is the only muscle that will act to abduct (open) the vocal cords?

Answer 24

Posterior cricoarytenoid

Question 25

What determines the position of the true vocal cords?

Answer 25

Vocalis muscle: insert onto the inner surface of the thyroid cartilage, but posteriorly they are attached to the arytenoid cartilages which can rotate on top of the cricoid cartilage
=rotation of the arytenoid cartilages alter the shape of the rima glottidis

Question 26

What is the nerve supply to the muscles of the larynx?

Answer 26

Recurrent laryngeal nerve of the vagus (CN X)

• right and left
• cricothyroid muscle is innervated by the external branch of the superior laryngeal nerve

Question 27

What are the steps of the cough reflex?

Answer 27

-inspire and fill lungs with air
-vocal cords adduct
-expiratory muscle contract to increase pressure
-intrathoracic pressure increases
-cords suddenly become abducted
=explosive outflow of air

Question 28

What happens if the movement of one vocal cord is impaired?

Answer 28

-phonation and cough will be impaired

Question 29

What is pitch of sound determined by?

Answer 29

Tension
High pitched sound: vocal cords taut
Low pitched sound: vocal cords less taut
=caused by bilateral contraction of cricothyroid muscle which increased tension in vocal cords (found outside the larynx)

Question 30

What can cause hoarseness of voice particularly when attempting high pitched sounds?

Answer 30

Injury to the external branch of the laryngeal nerve (CN X)

• this nerve is close to the superior thyroid artery
• can be injured in surgery

Question 31

What happens to the larynx when we swallow?

Answer 31

Elevates and moves anteriorly, so it lifts off the pharynx which sits behind it (thyrohyoid membrane suspends larynx from hyoid bone)
-suprahyoid muscles elevate and displace the hyoid bone and therefore the larynx

-posterior part of the tongue pushes food bolus up towards the soft palate, the posterior displacement of the tongue flattens the epiglottis. This combined with the aryepiglottic muscles contracting and adduction of vocal cords, narrows the laryngeal inlet and brings epiglottis from a verticle to more horizontal position

Question 32

What are the 2 key branches of the vagus nerve to do with the larynx?

Answer 32

Superior laryngeal nerve: gives internal and external branch

• internal: pierces thyrohyoid membrane and supplies sensory innnervation to supraglottic region and sensory to true vocal cords
• external: motor innervation to cricothyroid muscle

Recurrent laryngeal nerve (runs upwards in tracheoesophageal groove)

• sensory innervation to subglottis
• motor innervation to intrinsic muscles

Question 33

What is the journey of the recurrent laryngeal nerve?

Answer 33

-arises distally from the vagus
-passes anteriorly to then loop under right SCA, and on the left the arch of the aorta
-it then ascends in the tracheoesophageal groove
(close relationships to thyroid glad and inferior thyroid arteries)

Question 34

How do you get injury to the recurrent laryngeal nerve?

Answer 34

• during thyroid surgery as it is in a close relation to inferior thyroid arteries
• aortic arch aneurysm (left RLN)
• cancer involving apex of the lung (right RLN)
• disease/surgery involving larynx/oesophagus/thyroid

=RNL lesions> unilateral vocal cord palsies (hoarse voice, ineffective cough)
-often contralateral side compensates (crosses midline to meet vocal cord on affected side)

Question 35

What do paralysed vocal cords look like?

Answer 35

They assume a paramedian position (b/w fully adducted and fully abducted)

Question 36

What happens when there is a bilateral lesion to RLN?

Answer 36

-both vocal cords paralysed and in paramedian position
-narrow rima glottidis
=significant airway obstruction requiring emergency surgical airway

Question 37

What is the gag reflex?

Answer 37

Use a tongue depressor and touch the oropharynx
-sensory is glossopharyngeal nerve (afferent)
Brainstem
-motor is vagus nerve (efferent- comes back via left and right side to give symmetrical response)