Session 12: Larynx Flashcards
Describe the Larynx
The Larynx connects the inferior Oropharynx to the Trachea. It also contains the voice box. The Larynx extends from the Laryngeal Inlet, through which it communicates with the Laryngopharynx to the level of the inferior border of the cricoid cartilage. Here the laryngeal cavity is continuous with the Trachea.
- The laryngopharynx extends from the superior border of the epiglottis to the oesophagus at the level of the inferior border of the cricoid cartilage. It lies behind the laryngeal inlet. On each side of the inlet, the cavity of the laryngopharynx has a small depression called the piriform fossa.
The Larynx’s most vital function is to guard the air passages, especially during swallowing when it serves as the sphincter/valve of the lower respiratory tract, thus maintaining the airway. It is also important in the cough reflex.
- Respiration (open valve)
- Phonation (partially closes valve)
- Protecting trachea/bronchial tree (during swallowing) - stopping aspiration
- Cough Reflex
What is meant by the Laryngeal skeleton? What cartilages is it made up of?
The larynx is located between the hyoid bone above and the trachea below (vertebral level C4 and C6). It is slung from the hyoid bone by the thyrohyoid membrane and the thyrohyoid muscle.
Made up of the Hyoid Bone and 9 Cartilages:
3 Unpaired Cartilages
- Epiglottis
- Thyroid Cartilage
- Cricoid Cartilage
1 important set of Paired Cartilages
- Arytenoid Cartilage(s)
2 other sets of Paired Cartilages
- Corniculate Cartilage(s)
- Cuneiform Cartilage(s)
Describe the Epiglottis
- Leaf shaped elastic fibrocartilage
- Attached by ligaments anteriorly to the back of the hyoid bone and posteriorly to the thyroid cartilage (thyroepiglottic ligament)
- The vallecula is the depression between tongue base and epiglottis and is where food goes in the early stages of swallowing.
- The sides of the epiglottis are connected to the arytenoids by aryepiglottic folds that run backwards to from the margins of the entrance, of aditus, of the larynx.
Describe the Thyroid Cartilage
- Laryngeal Prominence (‘Adam’s Apple’) – made up 2 lateral plates (lamina) meeting in the midline.
- Shield-like
- Upper surface used to Mark C4 Level
- Bifurcation of common carotid artery
- Level of carotid body
- 2 horns
- Superior Thyroid Horns => Ligament => Hyoid Bone
- Inferior Thyroid Horn => Synovial Joint with Cricoid
Describe the Cricoid Cartilage and the Significance of the Cricotracheal Membrane
- Signet Ring Shaped
- Only complete ring of cartilage throughout the respiratory tract
- Most inferior cartilage
- 2 Articular facets on each side
- Lateral surface for the medial surface of Inferior horn of thyroid cartilage
- Superolateral surface for Arytenoid Cartilage
- Surface marking for C6 Level
- Inferiorly, the cricoid is attached to the trachea by the cricotracheal membrane.
- The arytenoids sit one on each side of the posterior signet
The cricotracheal membrane connects all the cartilages and its upper edge is slightly thickened to form the vocal ligament; anteriorly the membrane is thickened as the cricothyroid ligament that is easily felt and is used in emergency cricothyroid puncture for laryngeal obstruction.
Describe the Arytenoid Cartilages
- Pyramid shaped
- Crucial in vocal cord movement
- Concave base articulating with cricoid (sit on top)
- Anterior – Vocal process
- Lateral – Muscular process
- They are very mobile and involved in vocal cord movement – attached to the vocal cords.
What is at C1, C2, C3, C4/5 and C6?
What is the Cricovocal Membrane/Ligament?
- A.k.a. Conus Elasticus / Lateral Cricothyroid ligament
- Consists mainly of elastic fibres
- Lower border attached to cricoid cartilage
- Upper, Free Border = Vocal Ligament
- Attached to the deep surface of the angle of the thyroid cartilage
- Vocal process of arytenoid cartilage
Describe the Internal Larynx Divisions
The internal cavity of the larynx is divided into three spaces:
Passing forwards from the arytenoids to the back of the thyroid cartilage (just below the epiglottic attachment) are two folds of the mucosa lining the interior of the larynx. The upper is the vestibular fold, forming on each side, the false vocal cord. The lower fold, the true vocal cord (or fold) contains the vocal ligament. The space between the vocal records is the rima glottides. The mucosal folds demarcate the larynx into 3 zones.
-
Supraglottic space (vestibule)
- Laryngeal Inlet (inferior surface of epiglottis) =>
- Vestibular folds (false vocal cords)
-
Glottis
- Vocal Cords and Rima Glottis (space between true and false vocal cords) – including 1cm inferior to vocal cords
-
Subglottic Space
- Below true vocal cords =>
- Lower border of Cricoid Cartilage (first tracheal ring)
Describe the muscles of the larynx including their nerve supply in particular the Cricothyroid
The muscles of the larynx function to open the glottis in inspiration, close the vestibule during swallowing and alter the tone of the true vocal cords in phonation.
Extrinsic Muscles, which move the entire larynx
- Infrahyoid muscles
- Depress larynx and hyoid bone
- Suprahyoid muscles
- Elevate larynx
Intrinsic Muscles, which act on the:
- Vocal folds
- Open and close glottis
- Aryepiglottic folds
- Help to close the laryngeal inlet
The Recurrent Laryngeal Nerve supplies the intrinsic muscles. The exception is the Cricothyroid Muscle, which is supplied by the External Laryngeal Nerve.
The Cricothyroid muscle is the only external muscle of the larynx and functions in tensing the vocal cord (the only muscle to do so) by its slight tilting action on the cricoid cartilage.
The remaining muscles constitute an encircling sheet and have a sphincter action. One of these muscles, the posterior cricoarytenoid on each side) rotate the arytenoids outwards, thus separating the vocal cords.
Describe the layers of the vocal cords. What does the lack of a submucosa mean?
- Stratified Squamous Epithelium (superficial)
- Reinke’s space (oedematous, watery)
- Vocal Ligament
- Vocalis Muscle
The mucosa is firmly adherent to the vocal ligament, with no intervening submucosa. This lack of a submucosa means that:
- Vocal cords look pearly white avascular on laryngoscopy
- No oedema during infections (no fluid fluid can collect underneath the vocal cords)
- Delayed spread of carcinoma of vocal cords
Describe the movements of the vocal cords
Intrinsic Muscles of the Larynx move the vocal cords
- Abduction – Posterior Cricoarytenoid
- ONLY muscle which opens the true vocal cords
- Adduction – Lateral Cricoarytenoid
Cricothyroid
- Only intrinsic muscle on the outside
- Increases vocal cord tension
- Only intrinsic muscle not supplied by Recurrent Laryngeal Nerve
- Supplied by External Laryngeal Nerve
Describe the Sensory and Motor innvervation of the Larynx
The Larynx is innervated by Branches of the Vagus Nerve (CN X).
Superior Laryngeal Nerve
- Deep to carotid arteries
- Internal Laryngeal Nerve – pierces the thyrohyoid membrane, Sensory supply to Larynx above true vocal cord
- External Laryngeal Nerve – deep to superior thyroid artery, Motor to Cricothyroid Muscle
Recurrent Laryngeal Nerve
- Sensory supply to the area below the true vocal cord
- Motor to all intrinsic laryngeal muscles (except Cricothyroid)
Describe the course of the recurrent laryngeal nerve on both sides
The recurrent laryngeal nerve arises from the Vagus Nerve (CN X).
Right Recurrent Laryngeal Nerve
- Descends to T2
- Curves around (under) the Subclavian Artery
Left Recurrent Laryngeal Nerve
- Descends to T4
- Curves around the Arch of the Aorta
The nerves then course back up the neck to the larynx, lying between the trachea and oesophagus in the trachea-oesophageal grove before piercing the thyrohyoid membrane.
The nerves (superior and recurrent laryngeal) are accompanied by arterial branches from the superior and inferior thyroid arteries. The knowledge of this relationship is of considerable practical importance in thyroidectomy.
Describe how Recurrent Laryngeal Nerve palsy can lead to hoarseness of voice presentation
Pathology in the neck and chest can cause Recurrent Laryngeal Nerve palsy, leading to intrinsic laryngeal muscle weakness. This presents as hoarseness of voice. Hoarseness for longer than three weeks is a red flag symptom and needs evaluation to exclude malignancy.
Some causes of Hoarseness of Voice:
- Idiopathic
- Laryngeal cancer
- Thyroid disease (benign or malignant)
- Trauma including iatrogenic e.g. thyroidectomy
- Cervical lymphadenopathy
- Oesophageal cancer
- Aortic aneurysm
- Neuropathic (diabetes)
- Infection
- Laryngitis – Viral, Streptococcal
- Overuse of the voice
- GORD – Gastro Oesophageal Reflux
- Benign nodules on vocal cords (Singers)
- Apical Lung Tumour
- Recurrent Laryngeal Nerve Palsy (Both sides)
- Bronchial Carcinoma
- Left Recurrent Laryngeal Nerve Palsy (right doesn’t go low enough)
Describe the vasculature supply to the larynx
The Larynx is supplied by the Superior and Inferior Laryngeal Arteries, which are branches of the Superior and Inferior Thyroid Arteries respectively.
- External Carotid Artery => Superior Thyroid Artery => Superior Laryngeal Artery
- Subclavian Artery => Inferior Thyroid Artery => Inferior Laryngeal Artery
Venous Drainage of the Larynx
The larynx is drained by the Superior and Inferior Laryngeal Veins, which accompany the corresponding arteries.
- The Superior Laryngeal Vein joins the Superior Thyroid Vein before draining into the Internal Jugular Vein.
- The Inferior Laryngeal Vein joins the Inferior Thyroid Vein, which empties into the Left Brachiocephalic Vein.
NB: Superior Laryngeal Nerve and Recurrent Laryngeal Nerve are in very close proximity to the arterial supply
