56 - 60 Physiology SBAs for the Primary FRCA
Question 56
A 24 year old female professional singer notices difficulty hitting those high notes after thyroid surgery.
Which of the following most accurately describes the role of cricothyroid?
- Adducts the vocal cords
- Abducts the vocal cords
- Tenses the vocal cords
- Relaxes the vocal cords
- Elevates the larynx
Answer
- Tenses the vocal cords
Cricothyroid is supplied by the external branch of the superior laryngeal nerve and adjusts the tension of the cords by tilting the thyroid cartilage in relation to the cricoid.
- Adduction is done by lateral cricoarytenoid and interarytenoid
- Abduction is done by posterior cricoarytenoid
- Relaxation is done by vocalis and thyroarytenoid
Question 57
You have just intubated an elderly gentleman for an elective inguinal hernia repair, and your consultant starts asking you about the extrinsic muscles of the larynx
Which of the following is incorrect?
- Omohyoid elevates the larynx
- Extrinsic muscles are crucial during swallowing
- Suprahyoid muscles elevate the hyoid
- Geniohyoid elevates the larynx
- Infrahyoid muscles depress the hyoid
Answer
- Omohyoid elevates the larynx
The extrinsic muscles of the larynx move the whole apparatus up or down in the neck, rather than adjusting the cords, which is done by the intrinsic muscles.
The extrinsic muscles are crucial for swallowing and airway protection.
The two groups are:
- Suprahyoid - move the larynx up and forwards during swallowing
- Infrahyoid - move the larynx down and back after swallowing
Suprahyoid muscles
- Digastric
- Mylohyoid
- Geniohyoid
- Stylohyoid
Infrahyoid muscles
- Sternohyoid
- Sternothyroid
- Omohyoid
- Thyrohyoid
Innervation
Suprahyoids:
- Anterior belly of digastric and mylohyoid - V3 of trigeminal nerve
- Posterior belly of digastric and stylohyoid - Facial nerve
- Geniohyoid - hypoglossal nerve
Infrahyoids:
- Thyrohyoid - hypoglossal
- All the others - ansa cervicalis (C1-C3)
Question 58
You are the intensive care registrar reviewing a patient on the ward who has aspirated and now has a grumbling pneumonia.
The anaesthetic core trainee, who is sitting their exam next week, bets you £5 you can't name the nerve that supplies sensation to the mucosa immediately above the vocal cords.
Which nerve supplies this area?
- External branch of superior laryngeal nerve
- Internal branch of superior laryngeal nerve
- Recurrent laryngeal nerve
- Glossopharyngeal nerve
- Hypoglossal nerve
Answer
- Internal branch of superior laryngeal nerve
The internal branch of the superior laryngeal nerve supplies sensation of the mucosa from the epiglottis to the vocal cords.
The external branch provides motor supply to cricothyroid.
The recurrent laryngeal nerve supplies the mucosa below the cords.
The glossopharyngeal nerve supplies the mucosa of the pharynx but not the larynx.
The hypoglossal nerve is purely motor supply to the tongue.
Question 59
You're thrilled to be able to see the epiglottis on the screen of your videolaryngoscope, but rather less thrilled when the consultant asks you what type of cartilage it's made from.
Which of the following is correct?
- Elastic
- Fibrocartilage
- Calcified cartilage
- Hyaline cartilage
- Fibrous tissue
Answer
- Elastic
The epiglottis made of elastic cartilage, which helps maintain its flexibility.
- Fibrocartilage is found in intervertebral discs
- Hyaline cartilage is found in the thyroid, cricoid and bases of the arytenoids
- Calcified cartilage is a thin, middle layer in joints, found between the main articular (hyaline) cartilage and the underlying bone
- Fibrous tissue is found in tendons and ligaments, among other places, but is not relevant to the epiglottis
Question 60
You are called to see a patient in recovery as they have developed a hoarse voice after an elective thyroidectomy.
You are concerned about a nerve injury.
Which of the following is least likely to be affected?
- Vocalis
- Cricothyroid
- Thyroarytenoid
- Posterior Cricoarytenoid
- Thyroepiglotticus
Answer
- Cricothyroid
The nerve you're worried about is the recurrent laryngeal nerve, and the only intrinsic muscle listed that it doesn't supply is cricothyroid, which adjusts the tension of the cords.
- This is supplied by the external branch of the superior laryngeal nerve
We have asked this question twice because the examiners seem to love it.
The hoarseness is largely due to unilarteral weakness of posterior cricoarytenoid, which is the sole abductor of the cords.
Bilateral RLN palsy would cause stridor and obstruction requiring intubation.
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