S10) Functional Anatomy and Disorders of the Larynx Flashcards
What is the larynx?
The larynx is a ‘tube’ created by series of ligaments/membranes, cartilages and muscles
Describe the anatomical location of the larynx
The larynx lies below the hyoid bone:
- Begins at laryngeal inlet (aditus)
- Continues as the trachea (lower border of cricoid cartilage)
Describe the respective routes of inspired air and food into the body
- Inspired air: nasal cavity → nasopharynx → oropharynx → larynx → trachea
- Food: oral cavity → oropharynx → laryngopharynx → oesophagus
What is the main function of the larynx?
The main function of larynx is to provide a protective sphincter for the lower respiratory tract
Besides acting as a sphincter, state some other functions of the larynx
- Allows movement of air into/out of the lungs (ventilation)
- Allows us to cough
- Production of sound (phonation)
Identify and describe the three zones in the larynx
- Supraglottis (/vestibule): above the false vocal cords
- Glottis: between false and true vocal cords
- Subglottis: between true vocal cords and first tracheal ring
Identify the three single cartilages forming the framework of the larynx
- Thyroid
- Cricoid
- Epiglottis
Identify the three paired cartilages forming the framework of the larynx
- Arytenoid cartilages
- Corniculate cartilage
- Cuneiform cartilage
Numerous membranes/ligaments connect to the cartilages to help shape the larynx.
Identify them
- Thyrohyoid membrane (superior attachment of larynx)
- Cricothyroid membrane (inferior attachment of larynx)
- Cricotracheal membrane
- Quandrangular membrane
Label the following structures in the diagram below:
Describe the attachments of the epiglottis
- The epiglottis is attached anteriorly to the body of the hyoid and posteriorly to the back of the thyroid cartilage
- The sides are attached to the arytenoid cartilages by epiglottic folds which run backwards
What are the aryepiglottic folds and where are they found?
- The aryepiglottic folds are triangular folds of mucous membrane enclosing ligamentous and muscular fibres
- They are located at the entrance of the larynx, extending from the lateral borders of the epiglottis to the arytenoid cartilages, forming the aditus of the larynx
Describe the structure of the thyroid cartilage
The thyroid cartilage is shield-like, composed of two lateral plates meeting in the midline as prominent V – the laryngeal prominence (aka Adam’s apple)
Describe the structure of the cricoid cartilage
The cricoid cartilage is a signet-shaped ring and the only complete ring of cartilage throughout the respiratory tract
Describe the formation of the vestibular and vocal ligaments respectively
- Vestibular ligament is formed from the free lower border of quadrangular membrane (false vocal cords)
- Vocal ligament is formed from the upper free border of cricothyroid ligament-thickened edge (true vocal cords)
What is the rima glottidis?
The rima glottidis is the opening between the true vocal cords and the arytenoid cartilages in the larynx
Describe the anatomical relationship of the larynx and laryngopharynx
The larynx lies anterior to the laryngopharynx
Mucosal folds internally divide larynx into three regions.
Identify them and their respective contents
What is the ventricle and what does it do?
- The ventricle is a small recess found between the vestibular and vocal folds, which leads superolaterally into the saccule (sinus)
- It contains mucous glands that keep vocal folds moist
The larynx is lined with a mucous membrane.
What type of epithelium is found?
Pseudostratified ciliated columnar epithelium
What kind of epithelium lines the true vocal cords?
Stratified squamous epithelium
In the following laryngoscopic view of the larynx, label the structures below:
- Root of tongue
- Epiglottis
In the following laryngoscopic view of the larynx, label the structures below:
- Aryepiglottic folds
- Vestibular fold
- Vocal fold
In the following laryngoscopic view of the larynx, label the structures below:
- Rima glottidis
- Arytenoid cartilages
- Piriform fossae
What is intubation?
Intubation is the process of inserting and securing an endotracheal tube into a patient’s trachea to allow for ventilation and oxygenation
How is a nasoendoscopy performed?
Nasoendoscopy: insert flexible endoscope via nasal cavity and pharynx to then visualise larynx
What are the two main functions of the laryngeal muscles?
- Alter size and shape of the inlet
- Move position ± alter tension in vocal folds (cords)
Identify 3 overall functions of the laryngeal muscles
- Close larynx during swallowing
- Open larynx during inspiration and expiration
- Control movements of vocal cords in phonation and cough reflex
What are the cricothyroid and posterior cricoarytenoid muscles?
- Posterior cricoarytenoid muscle is the only intrinsic muscle of the larynx which abducts the true vocal cords
- Cricothyroid muscle is the only intrinsic muscle of the larynx found on the outside of the larynx
Intrinsic muscles play key role in the movement of vocal cords.
Describe their innervation
- Intrinsic muscles innervated via recurrent laryngeal nerve of vagus (CN X)
- Cricothyroid muscle innervated via superior laryngeal nerve of vagus (CN X)
Describe the vocal cord movements during breathing and phonation
- Vocal cords abduct during breathing to widen the glottis
- True vocal cords adduct during phonation and force expired air through adducted vocal cords to vibrate a column of air
Describe the vocal cord movement during a cough
During a cough (explosion of compressed air), the vocal cords are powerfully adducted to build intrathoracic pressure, then suddenly abducted
Illustrate how the pitch of vocal sound can be altered by tension and length of true vocal cords
- High-pitched sounds → vocal cords are taut
- Low-pitched sounds → vocal cords are relaxed
What does the cricothyroid muscle do?
The cricothyroid muscle tilts the thyroid cartilage forward on the cricoid cartilage to increase the length and tension in the vocal cords
What happens when the external branch of superior laryngeal nerve is damaged?
Injury to the nerve leads to hoarseness of voice especially when attempting high pitched sounds (paralysed cricothyroid muscle)
What changes happen to the larynx and supporting structures to protect the airwards from food/fluid during swallowing?
- Aryepiglottic muscle contract to narrow laryngeal inlet & pull down epiglottis
- Larynx is elevated (upward & forward) by pharyngeal suprahyoid muscles
- Vocal cords (glottis) close
The superior laryngeal nerve is a branch of the vagus nerve (CN X).
Describe the actions of its internal and external branches
- Internal branch: sensory innervation above vocal cords (supraglottic region)
- External branch: motor innervation to cricothyroid muscle
Describe the anatomical course of the recurrent laryngeal nerve
⇒ Arises distally, looping under the SCA (right) / the aortic arch (left)
⇒ Ascends in tracheo-oesophageal groove
Describe the motor and sensory functions of the recurrent laryngeal nerve
- Motor innervation: intrinsic muscles of larynx (except cricothyroid)
- Sensory innervation: below vocal cords (infraglottic region)
Describe the anatomical relations of the recurrent laryngeal nerves
- Inferior thyroid arteries (both)
- Aortic arch (left RLN)
- Apex of lung (right RLN)
When might the recurrent laryngeal nerve be injured?
Potentially injured during disease or surgery involving larynx, oesophagus or thyroid:
- Pancoast tumour (apex of lung)
- Thyroid surgery
- Aortic arch aneurysm
What happens when a vocal cord is paralysed?
Paralysed vocal cord assumes a paramedian position (between fully abducted and fully adducted)
Unilateral RLN lesions lead to unilateral vocal cord palsies.
What is the physiological effect of this?
- Unilateral palsy may lead to hoarseness of voice (± ineffective cough)
- Often contralateral side compensates (crosses midline to meet vocal cord on affected side)
Bilateral RLN lesions lead to bilateral vocal cord palsies.
What is the physiological effect of this?
- Both vocal cords paralysed and in paramedian position
- Presents with a narrow glottis (significant airway obstruction – emergency surgical airway needed)
Identify 6 clinical conditions which could affect the larynx
- Laryngitis
- Laryngeal nodules
- Laryngeal cancer
- Croup
- Epiglottitis
- Laryngeal oedema e.g. allergic reaction
Certain conditions causing swelling of the larynx can threaten the airway.
How will the patient present?
- Stridor
- Raised RR
- Distress
- Hypoxia
- ± Cyanosis
What is a cricothyroidotomy?
A cricothyroidotomy is an emergency procedure wherein an incision is made through the skin and cricothyroid membrane to establish a patent airway during certain life-threatening situations
What is croup?
- Croup is a common childhood illness caused by the inflammation of the upper respiratory tract (larynx & trachea, ± bronchi) as a result of a viral infection
- It presents with a harsh barking cough, hoarse voice and inspiratory stridor
What is epiglottitis?
- Acute epiglottitis is a condition in which there is inflammation of the epiglottis (± soft tissues surrounding the epiglottis)
- It is potentially life-threatening if complete obstruction of the airway occurs
Identify the following structures in the diagram below:
Identify the structures 1-3 in the diagram below:
Identify the structures 4-6 in the diagram below:
Identify the structures 7-11 in the diagram below:
Identify the structures 1-4 in the diagram below:
Identify the structures 5-7 in the diagram below:
Identify the structures 1-5 in the diagram below:
Identify the structures 6-10 in the diagram below:
Identify the structures 11-15 in the diagram below:
Identify the 9 structures/regions an endotracheal tube passes through/close to in order to reach the trachea
⇒ Oral cavity
⇒ Posterior 1/3 of tongue
⇒ Oropharyngeal isthmus
⇒ Supraglottis
⇒ Epiglottis & aryepiglottic folds
⇒ False vocal cords
⇒ True vocal cords
⇒ Infraglottis
⇒ Trachea
Identify the afferent and efferent limbs of the gag reflex
- Afferent limb (sensory): glossopharyngeal nerve (CN IX)
- Efferent limb (motor): vagus nerve (CN X)
What is the cervical plexus?
The cervical plexus is a network of nerve fibres that provides innervation to some of the structures in the neck and trunk
Where is the cervical plexus located?
It is located in the posterior triangle of the neck, halfway up the sternocleidomastoid muscle, and within the prevertebral layer of cervical fascia
Describe the formation of the cervical plexus
The plexus is formed by the anterior rami of cervical spinal nerves C1-C4
What is the ansa cervicalis and what does it do?
The ansa cervicalis is a loop of nerves, formed by nerve roots C1-C3, which off four motor branches to the infrahyoid muscles:
- Superior belly of omohyoid
- Inferior belly of omohyoid
- Sternohyoid
- Sternothyroid
Describe the anatomical location of the ansa cervicalis
The ansa cervicalis lies deep to the sternocleidomastoid and superficial to the internal jugular vein in the carotid sheath
Which nerve roots contribute to the phrenic nerve and which structure does it innervate?
- Nerve roots: C3, C4, C5
- Function: motor innervation to diaphragm
Which areas of the scalp, head and neck receive sensory innervation from the cervical plexus?
The cutaneous branches of the cervical plexus supply the skin of the neck, upper thorax, scalp and ear
What relationship does the posterior border of the sternocleidomastoid muscle have with the sensory branches of the cervical plexus?
- These sensory branches all enter the skin at the middle of the posterior border of the sternocleidomastoid
- This area is known as the nerve point of the neck (Erb’s point)
How might Erb’s point be used clinically?
At Erb’s point, a cervical plexus block is used to provide regional anaesthesia, usually for surgery in the neck region e.g. thyroidectomy, cervical lymph node excision
Describe the anatomical location of the thyroid gland
The thyroid gland is a midline structure located in the anterior triangle of the neck, encircled by pre-tracheal fascia, and spanning between the C5-T1 vertebrae
Describe the anatomical relations of the thyroid gland
- Superior: thyroid cartilage
- Anterior: sternohyoid & sternothyroid muscles
- Posterior: cricoid cartilage & trachea
- Lateral: carotid sheath
How do we test the function of the thyroid gland?
Thyroid function tests – TSH, T4, (sometimes T3)
Label the following parts on the thyroid:
- Lateral lobes
- Isthmus
- Upper pole
- Lower pole
Goitre is a condition wherein the thyroid gland is enlarged.
What are its associated causes?
- Associated with a an overactive thyroid gland (hyperthyroid)
- Associated with an underactive thyroid gland (hypothyroid)
Where are the parathyroid glands in relation to the thyroid gland and how many are there?
State the function of the parathyroid gland
They are responsible for the production of parathyroid hormone, which acts to control calcium levels in the body
What is a ‘pyramidal lobe’?
- The pyramidal lobe of thyroid is a remnant of the thyroglossal duct which arises from the isthmus upwards along the midline (anterior to thyroid cartilage)
- It is a normal variant, seen as a third thyroid lobe and is present in 10-30% of the population
Why does the thyroid gland move up during swallowing?
The thyroid gland is invested in the pretracheal fascia which holds the gland onto the larynx and the trachea, so the thyroid follows the movements of the larynx during swallowing
Which collection of muscles lie anterior to the thyroid gland?
Infrahyoid muscles
Describe the general arterial supply of the thyroid gland
- Arterial supply via superior and inferior thyroid arteries
- Superior thyroid artery arises from external carotid artery whereas the inferior thyroid artery arises from the thyrocervical trunk (branch of the subclavian artery)
What is the thyroid ima artery and where might it be found?
- The thyroid ima artery is an uncommon variant of the blood supply to the inferior aspect of the thyroid gland, often associated with absent inferior thyroid arteries
- It comes from the brachiocephalic trunk of the arch of aorta, supplying the anterior surface and isthmus
Where might the thyroid ima artery cause difficulties for surgical access to the airway?
In surgical procedures, e.g. percutaneous tracheostomy, there is a risk of injury to the thyroid ima artery which could cause severe bleeding
Describe the venous drainage of the thyroid gland
- Venous drainage via superior, middle and inferior thyroid veins, which form a venous plexus
- The superior and middle veins drain into the internal jugular veins, whereas the inferior drains into the brachiocephalic vein
Which nerves lie in close proximity to the superior and inferior thyroid artery?
- Superior thyroid artery: external branch of the superior laryngeal nerve
- Inferior thyroid artery (branch): recurrent laryngeal nerves
