L18: applied anatomy of the larynx Flashcards
Describe the management for epistaxis
Simple first aid measures – stops most nose bleeds
If fails – attempt simple cautery/topical vasoconstrictors
If fails – anterior packing (nasal tampons)
If fails – posterior packing +/- surgical intervention (eg. SPA ligation)
List the functions of larynx
1) Airway protection – preventing food/fluid etc entering airways
2) Ventilation – for movement of air into/out of lungs
3) Key role in cough reflex – rapidly expel anything inadvertently entering airway
4) Role in phonation of sound
Describe the anatomy of the larynx
‘Tube’ created by ligaments, membranes, cartilages & muscles
Suspended from and lies below the hyoid bone
Part of the upper respiratory tract
Begins at the laryngeal inlet & ends at lower border of cricoid cartilage (C6)
Continues as the trachea
List the cartilages which help form the structural framework of the larynx
Epiglottis
Thyroid cartilage
Cricoid cartilage
Arytenoid cartilage
Describe the structural framework of the larynx (membranes and ligaments)
Thyroid cartilage is attached superiorly to the hyoid bone by the thyrohyoid cartilage
Cricothyroid membrane runs upwards from the cricoid cartilage -> thyroid cartilage (deep to this, giving a free upper margin)
Free upper margin attaches anteriorly to the inner surface of thyroid cartilage & posteriorly to arytenoid cartilages
Upper margin is thickened = vocal ligament -> gives shape and structure to the true vocal cord
Describe cricothyroidotomy
In acute laryngeal obstruction, cricothyroid membrane is punctured
Allows rapid access into the infraglottic area of the larynx
Provides a temporary solution until a more definitive airway can be established
Rare, but may be required in situations of ‘can’t intubate, can’t ventilate’
Describe the attachments of the epiglottis
Attachment to the hyoid & back of the thyroid cartilage
Sides of the epiglottis are connected to the arytenoids by aryepiglottic folds -> quadrangular membrane joins the sides of the epiglottis to the arytenoids, giving shape to these folds
This forms the margins of the entrance, or aditus, of the larynx
Describe the anatomy of the thyroid & cricoid cartilage
Thyroid cartilage – made up of two lateral plates meeting in the midline as a prominent ‘V’ = laryngeal prominence
Cricoid cartilage is the only complete ring of cartilage throughout the respiratory tract
Inferiorly, attached to the trachea by the cricotracheal membrane; arytenoids sit on top of the cricoid cartilages posteriorly, one on each side
Describe what creates the false and true vocal cord
False – free lower border of quadrangular membrane = vestibular ligament
True – free upper border of cricothyroid membrane = vocal ligament
-space in the middle between the true vocal cords is the rima glottidis
Describe the three divisions the larynx is divided into internally
1) Supraglottis – epiglottis up to & including the false cords
2) Glottis – below false cords, includes the true cords until ~1cm below
3) Infraglottis – below true VCs to inferior boundary of cricoid
Which epithelium lines the larynx?
Pseudostratified ciliated columnar epithelium
EXCEPT: the true vocal cords are lined with stratified squamous
Describe intubation (laryngoscopic view)
Anaesthetist will view the larynx using a laryngoscope
Process of intubation requires an ET tube, passed through the patient’s oral cavity, oropharynx, larynx, vocal cords – sits in the upper part of the trachea
ET tube has a small balloon at the end that is inflated -> tube remains in place (has a lumen which allows for mechanical ventilation and oxygenation of the patient’s lungs)
Describe the two main actions of the intrinsic laryngeal muscles
1) Alter size and shape of laryngeal inlet
- muscles within aryepiglottic folds can contract, narrow laryngeal inlet & flatten position of epiglottis
- protect larynx during swallowing
2) Alter tension in and position of true vocal cords
- muscles within larynx alter position of arytenoid cartilages (vary position of cords)
- protects larynx during swallowing and enables phonation
What nerve are the intrinsic laryngeal muscles supplied by?
Recurrent laryngeal nerve of vagus
Right half = right recurrent laryngeal nerve
Left half = left recurrent laryngeal nerve
EXCEPT: cricothyroid muscle – external branch of superior laryngeal nerve of vagus
Describe the function of the arytenoids and intrinsic laryngeal muscles
Majority of muscles act to narrow rima glottidis by adducting VCs together
Only posterior cricoarytenoid can abduct VCs (widens rima glottidis)
Arytenoids move relative to one another, alters position of true VCs & therefore size of aperture
List the true vocal cord movements
Breathing – VCs abducted
Swallowing – VCs adducted
Phonation – VCs closely adducted, VC vibration creates sound waves
Cough – VCs strongly adducted
Describe how different pitched sounds are produced
High-pitched sounds = vocal cords taut
Low-pitched sounds = vocal cords less taut
Contraction of both cricothyroid muscles = increases tension in vocal cords
-muscle located outside of larynx
Describe the action of cricothyroid muscle
Tilts thyroid cartilage forward on cricoid increasing tension in vocal cords – important for reaching higher pitch
Innervated by external branch of superior laryngeal nerve (branch of vagus)
Nerve is closely related to superior thyroid artery – risk of injury in thyroid surgery
Causes hoarseness of voice when attempting higher pitched sounds
Describe the larynx during swallowing
1) Tongue pushes epiglottis & aryepiglottic muscles contract -> narrows laryngeal inlet
2) Food/fluid directed over curved upper surface of epiglottis into piriform fossae of laryngopharynx (can be a site for foreign bodies to get stuck in)
3) Hyoid bone elevated & moved anteriorly by suprahyoid muscles (larynx moves up and forward)
4) Adduction of true vocal cords – closure of rima glottidis
List the sensory and motor nerves supplying the larynx
Internal branch of superior laryngeal nerve – sensory: supraglottis & glottis (true VCs)
External branch of superior laryngeal nerve – motor: cricothyroid muscle
Recurrent laryngeal nerve – motor: intrinsic muscles & sensory: infraglottis
Describe the route of the right and left recurrent laryngeal nerves
On right, passes anteriorly to and then loops under the right subclavian artery & on left, the arch of the aorta
Ascends in tracheo-oesophageal groove (behind lobes of thyroid gland)
Close anatomical relationship with thyroid gland & inferior thyroid arteries
Risk of damage to nerve in thyroid surgery = paralysis of muscles moving a true vocal cord
How can the recurrent laryngeal nerve be injured?
Disease or surgery involving larynx, oesophagus or thyroid
Aortic arch aneurysm (left RLN)
Cancer involving apex of lung (right RLN)
RLN supplies intrinsic muscles of larynx responsible for vocal cord movements
Describe a unilateral recurrent laryngeal nerve injury
Affected VC assumes a resting ‘paramedian’ position = between fully abducted and fully adducted
No significant impairment to airflow during breathing
Cannot adduct to meet VC opposite side – weak, ineffective cough & impaired phonation (hoarseness of voice)
Describe a bilateral recurrent laryngeal nerve injury
Both VCs assume a resting ‘paramedian’ position
Significant airway obstruction – emergency surgical airway (neither VC can abduct during breathing to widen rima glottidis)
