Functional Anatomy Of The Larynx

Question 1

Functions of the larynx?

Answer 1

Airway protection - prevents food/ fluid etc entering airways

Ventilation - movement of air into/ out of lungs

Role in cough reflex - rapidly expel anything inadvertently entering airway

Role in production of sound - phonation

Question 2

Where is the larynx?

Answer 2

Suspended from and lies below hyoid bone attached to thyrohyoid membrane/ infra-hyoids

Part of respiratory system (transmits air into/ out of lower rep. Tract)

Beings at laryngeal inlet (C3) and ends at lower border of cricoid cartilage (C6)

Anterior to laryngopharynx

Continues as trachea

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Question 3

What is the larynx made up from?

Answer 3

Cartilages, membranes and ligaments:

• Epiglottis superior
• Attached by stalk to inner surface of thyroid cartilage (laryngeal prominences)
• Small triangular arytenoid cartilages
• Cricoid cartilage (signet shape, wider at back, complete ring)
• Synovial joints between cartilages including cricothyroid and cricoarytenoid
• thyrohyoid membrane
  (suspends thyroid cartilage)
• cricothyroid membrane/ ligament (squishy, gain access airways emergency)
• cricotracheal membrane

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Question 4

What is a cricothyroidotomy?

Answer 4

Provides emergency access to airway, beneath vocal cords. If on rare occasion patient can’t be intubated or ventilated (e.g. swelling to vocal cords/ severe anaphylactic shock)

Cut cricothyroid ligament and membrane -> Insert tube

Question 5

What forms the laryngeal inlet?

Answer 5

epiglottis connects to arytenoid cartilage

Aryepiglottic folds (2) from lateral surface of epiglottis to Arytenoid cartilage

Quadrangular membrane from folds to superior free border of cricothyroid membrane

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Question 6

What are the false and true vocal cords, where are they? What lies between them?

Answer 6

False - vestibular ligament (fixed) attached to free lower border of quadrangular membrane

True - vocal ligament (mobile) attached to free upper border of cricothyroid membrane (inferior to false) (between two folds is rima glottidis) usually lighter in colour

Between the two folds is a small recess (ventricle) leads laterally and upwards into saccule/ sinus contains mucous glands that keep true vocal folds moist

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Question 7

What are the supraglottis, glottis and infraglottis made of? What creates these three regions?

Answer 7

Supraglottis: epiglottis to laryngeal vestibule, includes false cords

Glottis: narrowest part, includes true cords

Infraglottis/ subglottis: below true vocal cords -> bottom of cricoid cartilage

Mucosal folds internally divide larynx into three regions including medial mucosal fold and inferior mucosal fold. Larynx lined with a mucous membrane

Question 8

What type of epithelium lines the larynx?

Answer 8

Pseudostratified ciliated columnar epithelium (+ goblet cells)

Bar true vocal cords which are lined with stratified squamous

Question 9

What is intubation?

Answer 9

vocal cords must be viewed

Placement of an endotracheal tube into subglottic region (beckons vocal cords)

Question 10

What is a flexible nasoendoscopy?

Answer 10

Insert flexible endoscope via nasal cavity and pharynx to then visualise larynx

Question 11

Functions of the many laryngeal muscles

Answer 11

Broadly two main actions to alter size/ shape of laryngeal inlet and tension/ position of vocal cords

1. Swallowing - close laryngeal inlet and vocal cords, protect resp tract
2. Inspiration and expiration - open vocal cords and laryngeal inlet allowing movement of air
3. Phonation and cough reflex - laryngeal inlet open, aDducted vocal cords (quickly snap open)

Question 12

Which one of all the intrinsic laryngeal muscles aBducts the vocal cords?

Answer 12

Posterior cricoarytenoid

Question 13

How do intrinsic muscles of the larynx work? What Nerve innervates them?

Answer 13

Move cartilages relative to one another to change vocal cord movement
- arytenoid position on cricoid determines position of true vocal cords and therefore side of aperture (Roma glottidis)

All muscles supplied by recurrent laryngeal N of vagus bar cricothyroid muscle (external branch of superior laryngeal N)

Question 14

What do vocal cords do during phonation?

Answer 14

VCs closely aDducted, expired air forced through -> vibration creates sound waves

Similar to coughing reflex

Opposite to inspiration and expiration when fully aBducted

Question 15

How do we cough?

Answer 15

Cough - explosion of compressed air

1. Inspire and fill lungs with air
2. Vocal cords aDducted
3. Expiratory muscles contract
4. Intrathoracic pressure builds
5. Cords suddenly aBduct
6. Explosive outflow of air

Question 16

How is pitch determined by vocal cords? What can happen if this is impaired?

Answer 16

Higher pitch - vocal cords more stretched - bilateral contraction cricothyroid muscle (CN X, external branch of superior laryngeal nerve) tilts thyroid forwards

Low pitch sounds - vocal cords less taut

N closely related to superior thyroid artery - thyroid op damages nerve -> hoarseness of voice on attempting higher pitched sounds

Question 17

How does the larynx protect the airway from food and fluid when swallowing?

Answer 17

Hyoid bone elevated and moved anteriorly by suprahyoid muscles - larynx moves up and forward - tongue pushes epiglottis posteriorly and aryepiglottic muscles contract - narrowed laryngeal inlet - closure of vocal cords

Question 18

What role do suprahyoids and longitudinal pharyngeal muscles have in swallowing?

Answer 18

Act to elevate and anteriorly displace larynx and ensure patency of pharynx so food/ fluid can be directed into it

Question 19

Explain the vagus Nerve innervation to the larynx

Answer 19

Vagus Nerve gives off two branches:
- recurrent laryngeal -> sensory to subglottic & motor to intrinsic muscles

AND

• superior laryngeal -> internal branch to sensory sulraglottic and glottic
  and external branch to motor cricothyroid

(Autonomic also delivered via CNX to mucosal glands within larynx)

Question 20

Describe the route of the recurrent laryngeal Nerve

Answer 20

Arises dietary from vagus -> passes anteriorly to then loops under right SCA and on left arch of aorta -> ascends in tracheo-oesophageal grove (close to thyroid gland and inferior thyroid arteries) -> innervated all intrinsic muscles of larynx (except cricothyroid) and provides sensory of and below VCs

Question 21

How might you get an injury to the recurrent laryngeal nerve?

Answer 21

• Close inferior thyroid artery so thyroid surgery
• aortic arch aneurysm (left)
• cancer involving apex of lung (right)
• disease or surgery larynx/ oesophagus/ thyroid

Unilateral lesion -> unilateral VC palsy -> hoarse voice and ineffective cough (often controlateral side compensates in time)

Bilateral lesion -> both Vcs paralysed and paramedian -> narrow glottis -> significant airway obstruction -> emergency surgical airway

Paralysed Vcs assume paramedian position (between aBduction and ADd)

Question 22

What conditions affect the larynx? What signs might there be?

Answer 22

Laryngitis (inflammation of VCs)

Laryngeal nodules

Laryngeal cancer

Croup (viral swelling around Vcs)

Epiglottitis

Laryngeal oedema e.g. allergic reaction

Certain conditions causing swelling of the larynx can threaten the airway - patient with a compromised upper airway will present with stridor/ raised RR/ distress/ hypoxia/ cyanosis