SGW - larynx

Question 1

what is the gag reflex?

Answer 1

involuntary contraction of the muscles forming the pharynx (inner longitudinal + outer circular) in response to stimulation of the posterior pharyngeal wall

Question 2

what does stimulation of the posterior pharyngeal wall in gag reflex result in?

Answer 2

causes elevation of the soft palate and contraction of the pharyngeal muscles, preventing foreign bodies form entering the throat - helps prevent choking

Question 3

why does the presence or absence of gag reflex not determine whether a patient has a safe swallow?

Answer 3

different people have a different sensitivity to the reflex (some diminished, some even vomiting)
formal swallow assessment should be undertaken if worried

Question 4

what is the afferent limb of the gag reflex?

Answer 4

glossopharyngeal nerve (CN IX)

Question 5

what else can induce the gag reflex aside from stimulation to posterior pharyngeal wall?

Answer 5

touching soft palate

Question 6

what is the sensory innervation of the soft palate?

Answer 6

maxillary of trigeminal (CN V2)

supplies sensory to soft and hard palate as well as general sensation to anterior 2/3rd tongue

Question 7

what is the efferent limb of the reflex?

Answer 7

vagus nerve (CN X) - motor

Question 8

what does the motor nerve innervate to cause the gag reflex?

Answer 8

majority of palate elevators (e.g. Levator veli palatini from Ph A 4 + 6)
constrictors of the pharynx

(elevate palate to move block off nasopharynx, constrict pharynx for pharyngeal peristalsis)

Question 9

what can result in hoarseness of voice?

Answer 9

from ligation of inferior thyroid artery leading to unilateral damage to L/R recurrent laryngeal nerve (inferior thyroid artery runs lateral to recurrent laryngeal nerve on route to larynx)

Question 10

what does the recurrent laryngeal nerve supply?

Answer 10

(from vagus)
L + R supplies ALL INTRINSIC muscles of the LARYNX
EXCEPT cricothyroid muscles (external superior laryngeal nerve)

Question 11

which vocal cord is more often damaged / paralysed? why?

Answer 11

left, as it has a longer course from the brainstem to the larynx

Question 12

where does the recurrent laryngeal nerves travel before reaching the larynx?

Answer 12

loops under arch of aorta (L), or subclavian artery (R) before ascending up between trachea and oesophagus (trache-oesophageal groove) to reach the larynx

Question 13

what are other concerning causes of voice hoarseness?

Answer 13

pathology in structures closely related to the recurrent laryngeal nerve (on each side) may compress / infiltrate the nerve e.g.:

1. tumours of thyroid, oesophagus, lung (or operations of these structures) - think pre-tracheal fascia
2. enlarged lymph nodes within trachea-oesophageal groove

Question 14

what are pathologies near the left side of the recurrent laryngeal nerve that are of particular concern?

Answer 14

bronchial carcinoma

aortic arch aneurysm

Question 15

pathology to which other structure may also cause hoarseness?

Answer 15

larynx e.g. cancer of vocal cords

Question 16

why may patients with stroke / other neurological conditions e.g. MS present with hoarseness of voice?

Answer 16

may have involvement of the vagus nerve at the level of the brainstem - can develop difficulties in phonation and / or difficulties with swallowing

Question 17

which nerve supplies motor and sensory to the larynx?

Answer 17

superior laryngeal nerve and recurrent (inferior) laryngeal nerves of vagus (CN X)
(structural derivatives of Ph A 4 + 6)

Question 18

what does the internal laryngeal nerve innervate?

Answer 18

internal branch of superior laryngeal nerve

innervates laryngeal mucosa ABOVE vocal cords (supraglottic)

Question 19

what does the recurrent (inferior) laryngeal nerve innervate? (sensory)

Answer 19

mucosa BELOW vocal cords (infraglottic)

Question 20

what does the recurrent (inferior) laryngeal nerve innervate? (motor)

Answer 20

ALL intrinsic muscles of larynx
EXCEPT cricothyroid (external superior laryngeal nerve)

Question 21

summary of laryngeal innervation

Answer 21

vagus (supplies ALL)
superior laryngeal nerve + recurrent (inferior) laryngeal nerve are branches of vagus
superior laryngeal nerve has external (motor - cricothyroid) and internal (sensory supraglottic - because SUPERIOR nerve)
recurrent laryngeal has BOTH sensory (subglottic mucosa) and motor (ALL intrinsic muscles of larynx but cricothyroid)

Question 22

function of cricothyroid?

Answer 22

tilt thyroid cartilage (superior) forward on cricoid cartilage (inferior) to increase tension in the vocal cords (and help to ADduct them) - allows vocal cords to create higher pitched sounds

Question 23

symptoms a patient would present with if external branch of superior laryngeal nerve was damaged?

Answer 23

causes weakness / paralysis of cricothyroid - problems with phonation, particularly at higher pitches
can also cause mild hoarseness and fatiguability to the voice

Question 24

what does the external laryngeal nerve run in close proximity to?

Answer 24

it is the external branch of the superior laryngeal nerve
supplies cricothyroid muscle
external + internal branches run in close proximity to superior thyroid artery

Question 25

arterial supply to thyroid?

Answer 25

superior + inferior thyroid arteries

Question 26

supply of recurrent (inferior) laryngeal nerves?

Answer 26

motor: intrinsic muscles BUT cricothyroid
sensory: subglottic

Question 27

what do the intrinsic muscles of the larynx control?

Answer 27

entry into the airway (trachea)

vocal cord movement during phonation, coughing, swallowing and breathing

Question 28

what would unilateral recurrent laryngeal nerve damage result in?

Answer 28

voice change e.g. hoarseness and a weaker cough

Question 29

why may a patient with unilateral recurrent laryngeal nerve damage present with a weaker cough?

Answer 29

to cough, the vocal cords have to be firmly ADducted, before SNAPPING OPEN to allow expulsion of air from behind

Question 30

what may happen with time in patients with unilateral recurrent laryngeal nerve damage?

Answer 30

the vocal cord on the opposite side may compensate (by shifting closer towards midline), resulting in v little effect on phonation

Question 31

why is there not usually significant problems with breathing in unilateral recurrent laryngeal nerve damage?

Answer 31

the other vocal cord can still move freely
not significant obstruction to airflow through the rima glottidis - significant problems with breathing doesn’t usually occur

Question 32

what happens with bilateral recurrent laryngeal nerve damage?

Answer 32

BOTH vocal cords paralysed

speech will be significantly affected (aphonia)

Question 33

why does aphonia occur with bilateral recurrent laryngeal nerve damage?

Answer 33

vocal cords cannot move

Question 34

what will the resting position of the vocal cords as a result of bilateral recurrent laryngeal nerve damage lead to? how will patients present?

Answer 34

obstruct movement of air in and out of the trachea

patients present with stridor (high pitched, usually inspiratory) and with significant difficulties with breathing