Anatomy of the Larynx

Question 1

Where is the larynx located?

Answer 1

between pharynx and trachea

Opposite C3-C6

Question 2

What are the structures that form the framework of the larynx?

Answer 2

epiglottis, thyroid cartilage, cricoid and arytenoids

Question 3

What connects the hyoid bone to the larynx?

Answer 3

Larynx slung from the hyoid bone by the thyrohyoid membrane and the thyrohyoid muscle

Question 4

Where is the thyroid cartilage located?

Where are the membranes asssociated with it?

What is its joint?

Answer 4

Superior border at C4

• Thyrohyoid membrane-
  
  • median thyrohyoid ligament- anteromedial thickening
  • Lateral thyrohyoid ligament- posterolateral thickening
• Thyrohyoid muscle

Cricothyroid joint- inferior horns articulate with cricoid cartilage

Question 5

What is the key characteristic that differentiates the cricoid cartilage from other cartilages in the larynx

What vertebral level is the cricoid cartilage at?

What structures is it attached to and how?

Answer 5

Signet ring shaped- only complete ring of cartilage

C4

Sup.- thyroid cartliage

Inf- first tracheal ring- cricotracheal membrane

Posterior signet- arytenoids

Question 6

What are the two cartilage nodules located at the inlet of pharynx?

Answer 6

cuneiform- within margins of aryepiglottic fold

Corniculate cartilage- lying at the apex of arytenoids

no functional importance

Question 7

Where is the epiglottis located and what are its attachments?

Answer 7

The epiglottis is a leaf shape lying behind root of tongue

Sup.ant.- hyoepglottic ligament- hyoid

Inf.- thyroepiplottic ligament ( immediately above the vocal cords)- thyroid cartilage

Lat.- aryepiglottic folds (runs backwards to form the entrance of larynx)- aryetenoids

Upper anterior surface projects above hyoid bone

its mucosa is reflected forwards to base of tongue

Question 8

How does the epiglottis attach to the base of tongue?

Answer 8

At base of tongue raised up to median glossoepiglottic folds and lateral pharngoepiglottic folds

Depression between the two- vallecula

Question 9

What is the significance of cricothyroid membrane and what are its attachements?

Answer 9

Connects thyroid, crocoid and arytenoid cartilages

• composed of elastic tissue
• Attachements
  
  • Sup.- posterior surface of thyroid cartilage
  • Inf.- vocal process of arytenoid
• between attachments- upper edge thickened- vocal ligament
• Anteriorly, membrane thickens as cricothyroid ligament

Question 10

Use of cricothyroid ligament in emergency

Answer 10

cricothroid ligament is subcutaneous, easily felt and used in emergency cricothyroid puncture for laryngeal obstruction

Question 11

Where are the vocal cords located and what are the two folds of mucosa?

Answer 11

Arytenoids to back of thyroid- below epiglottic attachements

• Upper
  
  • Vestibular fold
  • Small amount of fibrous tissue
  • false vocal cords
• Lower
  
  • True vocal cords
  • vocal ligament
  • muscosa firmly adherent to to vocal ligament. No intervening submucosa. Gives pearly white avascular appearance of vocal cords seen on laryngoscopy
• Space between vocal cords-rima glottidis

Question 12

What is the piriform fossa and what is its significance?

Answer 12

Piriform fossa- recess on either side of larynx, in which swallowed foreighn bodies tend to lodge

Question 13

What is the function of muscles of larynx

Answer 13

• open glottis in inspiration
• close vestibule and glottis in deglutition
• alter tone of true vocal cords in phonation

Question 14

What is the role of intrinsic muscles?

Answer 14

Close larynx during swallowing

Question 15

List the intrinsic muscles and their levels of attachment

Answer 15

1. Aryepiglottic and oblique arytenoids- close aryepiglottic folds (which define the laryngeal inlet)
2. Thyroepiglottic muscles close the walls of vestibule of larynx
3. Lateral cricoarytenoids, interarytenoids- close the vocal cords

Question 16

What is the only intrinsic muscle that does not have a sphincter mechanism?

Answer 16

Posterior cricoarytenoid- upon contraction, this rotates the arytenoids outwards and seperates the vocal cords

Question 17

What is the only extrinsic muscle of the larynx?

Answer 17

Cricothyroid muscle

• between cricoid and thyroid cartilage
• lowers the thyroid cartilage forwards, distance between the vocal process of arytenoids is increased, vocal cords stretched

Question 18

What are the 3 ways in which food is prevented from entering the larynx

Answer 18

1. Closure of sphincter mechanism of larynx
2. Tucking the larynx behind the overhanging mass of the tongue
3. Using the epiglottis to guide the bolus away from the laryngeal entrance

Question 19

How does “tucking the larynx behind the overhanging mass of the tongue” work?

Answer 19

Larynx elevated and pulled forwards by actions of the suprahyoid muscles, thyrohyoid and stylopharyngeus muscles

Question 20

Process of preventing food from entering larynx

Answer 20

1. As head of bolus reaches epiglottis, it is tipped backwards against pharyngeal wall and momentarily holds up the passage of food
2. Larynx then elevated and pulled forwards by muscles
3. Epiglottis stand erect, guiding bolos into streams along the piriform fossa and away from laryngeal orifice
4. Then epiglottis flaps backwards as cover over the laryngeal inlet, but this only occurs after the main bolus of food has passed beyond it

Question 21

Nervous supply to the larynx

Answer 21

Vagus

• Superior laryngeal nerve
  
  • External- passes into cricothyroid muscle and supplies this
  • Internal- pierces thyrohyoid membrane with superior laryngeal vessel- supply mucosa of larynx down to vocal cords
• Recurrent laryngeal nerve- intrinsic muscles and mucosa below vocal cords
  
  • Right- arises as vagus n. crosses in front of right subclavian a., then passes back into larynx
  • Left- winds below aorta and ascends up

Question 22

What happens when the superior laryngeal nerve is damaged?

Answer 22

Weakness in phonation due to loss of tightening effect of cricothyroid muscle on the cord

Question 23

What happends if the recurrent nerve is bruised or partially damaged?

Answer 23

Semon’s law: The abductors ( posterior cricoarytnoids) are affected more than the adductors ( the rest of intrinic sphinctors)

The affected cord adopts to midline adducted position

In bilateral complete paralyis, the cords come together, stridor (high pitched, wheezing sound) is intense and tracheostomy may be essential

Question 24

What happens in complete division of the recurrent laryngeal nerve?

Answer 24

Cords on the affected side take up neutral position between abduction and adduction. Usually the other cord is able to compensate and speech is not greatly affected

If both nerves are affected, voice is completely lost and breathing becomes difficult through the only partially opened glottis

Question 25

What epithelium is the trachea lined by?

Answer 25

pseudostratified epithelium lined with cilia

Question 26

The cough reflex

Answer 26

1. Cought initiated by chemicals(cytokines) or mechanical(foreign body/cancer)
2. Activate sensory nerve endings, conveyed through vagus nerve to NTS in medulla
3. From here synapse with efferent- phrenic, spinomotor, recurrent laryngeal nerve
4. Activate effector muscles- respiratorym laryngeal, bronchial smooth muscles

Question 27

3 phases of cough reflex

Answer 27

• Inspiratory phase- deep breath - increased pressure within the lung
• Compression phase- glottis closes and respiratory muscles contract- increase pressure even further in the lungs
• Expiratory phase- glottis opens and air pushed out due to high pressure in lungs

Question 28

What are the three zones of larynx

Answer 28

Supraglottic compartment

false cords

Glottic compartment

True cords

Subglottic compartment

first tracheal ring