10. Muscles and innervation of the larynx

Question 1

what are the 2 main actions of laryngeal muscles

Answer 1

1. alter size/shape of laryngeal inlet

2. move position and alter tension of vocal cords

Question 2

what determines the position of the vocal cords and thus size of rima glottidis

Answer 2

position of arytenoids on cricoid cartilage (vocal ligaments are attached posteriorly to arytenoids)

Question 3

which muscle acts to abduct vocal cords

Answer 3

posterior cricoarytenoid (cricoid cartilage to arytenoid cartilage)

Question 4

describe the position of the vocal cords during respiration

Answer 4

vocal cords abducted to open rima glottidis

Question 5

describe the position o the vocal cords during the cough reflex

Answer 5

1. vocal cords powerfully adducted…
2. increased intrathoracic pressure…
3. cords suddenly abducted…
4. expel air and any material

Question 6

describe the changes in the larynx during swallowing

Answer 6

1. vocal cords adduct - close glottis
2. aryepiglottic muscle contraction - narrows laryngeal inlet and pulls on epiglottis so that it covers laryngeal inlet
3. assisted by elevation of larynx - suprahyoid and pharyngeal muscles pull larynx up and forwards

Question 7

describe the position of the vocal cords during phonation

Answer 7

adducted - expired air is forced through closely adducted vocal cords to vibrate column of air

Question 8

which muscle is important in phonation - how does it act

Answer 8

cricothyroid: only intrinsic laryngeal muscle to lie externally - bilateral contraction tilts thyroid cartilage on cricoid cartilage… increases stretch and tension in vocal cords… changes pitch of sound

Question 9

describe the stretch of vocal cords in producing high and low pitched sounds

Answer 9

• high-pitch: taut vocal cords

- low-pitch: relaxed vocal cords

Question 10

describe the innervation of the larynx

Answer 10

Branches of vagus n:

1. recurrent laryngeal n.
   - motor to all intrinsic laryngeal muscles (exc. cricothyroid)
   - sensory to infraglottis
2. superior laryngeal n.
   - external br: motor to cricothyroid
   - internal br: sensory to supraglottis

Question 11

during which surgery are the laryngeal nerves particularly at risk of damage

Answer 11

Thyroid surgery, due to close association between:

• superior thyroid artery and superior laryngeal n
• inferior thyroid artery and recurrent laryngeal n

Question 12

what are the effects of recurrent and superior laryngeal nerve palsies

Answer 12

• SLN palsy: weakness in phonation (esp. higher pitch) due to loss of tightening effect of cricothyroid on vocal cords
• RLN palsy: paralysis of vocal cords (complete/incomplete, unilateral/bilateral)

Question 13

what position do paralysed vocal cords adopt

Answer 13

paramedian position: between adducted and abducted

Question 14

what is the effect of unilateral and bilateral vocal cord paralysis

Answer 14

Unilateral:

• some hoarseness and weaker cough
• airflow is minimally affected
• contralateral side can often compensate in time (crosses midline to meet vocal cord on affected side)

Bilateral:

• extremely narrow rima glottidis causing impaired speech and breathing
• stridor, hypoxia and cyanosis
• signficant airway obstruction may need emergency tracheostomy