SGW - larynx Flashcards
what is the gag reflex?
involuntary contraction of the muscles forming the pharynx (inner longitudinal + outer circular) in response to stimulation of the posterior pharyngeal wall
what does stimulation of the posterior pharyngeal wall in gag reflex result in?
causes elevation of the soft palate and contraction of the pharyngeal muscles, preventing foreign bodies form entering the throat - helps prevent choking
why does the presence or absence of gag reflex not determine whether a patient has a safe swallow?
different people have a different sensitivity to the reflex (some diminished, some even vomiting)
formal swallow assessment should be undertaken if worried
what is the afferent limb of the gag reflex?
glossopharyngeal nerve (CN IX)
what else can induce the gag reflex aside from stimulation to posterior pharyngeal wall?
touching soft palate
what is the sensory innervation of the soft palate?
maxillary of trigeminal (CN V2)
supplies sensory to soft and hard palate as well as general sensation to anterior 2/3rd tongue
what is the efferent limb of the reflex?
vagus nerve (CN X) - motor
what does the motor nerve innervate to cause the gag reflex?
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)
what can result in hoarseness of voice?
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)
what does the recurrent laryngeal nerve supply?
(from vagus)
L + R supplies ALL INTRINSIC muscles of the LARYNX
EXCEPT cricothyroid muscles (external superior laryngeal nerve)
which vocal cord is more often damaged / paralysed? why?
left, as it has a longer course from the brainstem to the larynx
where does the recurrent laryngeal nerves travel before reaching the larynx?
loops under arch of aorta (L), or subclavian artery (R) before ascending up between trachea and oesophagus (trache-oesophageal groove) to reach the larynx
what are other concerning causes of voice hoarseness?
pathology in structures closely related to the recurrent laryngeal nerve (on each side) may compress / infiltrate the nerve e.g.:
- tumours of thyroid, oesophagus, lung (or operations of these structures) - think pre-tracheal fascia
- enlarged lymph nodes within trachea-oesophageal groove
what are pathologies near the left side of the recurrent laryngeal nerve that are of particular concern?
bronchial carcinoma
aortic arch aneurysm
pathology to which other structure may also cause hoarseness?
larynx e.g. cancer of vocal cords
why may patients with stroke / other neurological conditions e.g. MS present with hoarseness of voice?
may have involvement of the vagus nerve at the level of the brainstem - can develop difficulties in phonation and / or difficulties with swallowing
which nerve supplies motor and sensory to the larynx?
superior laryngeal nerve and recurrent (inferior) laryngeal nerves of vagus (CN X)
(structural derivatives of Ph A 4 + 6)
what does the internal laryngeal nerve innervate?
internal branch of superior laryngeal nerve
innervates laryngeal mucosa ABOVE vocal cords (supraglottic)
what does the recurrent (inferior) laryngeal nerve innervate? (sensory)
mucosa BELOW vocal cords (infraglottic)
what does the recurrent (inferior) laryngeal nerve innervate? (motor)
ALL intrinsic muscles of larynx EXCEPT cricothyroid (external superior laryngeal nerve)
summary of laryngeal innervation
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)
function of cricothyroid?
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
symptoms a patient would present with if external branch of superior laryngeal nerve was damaged?
causes weakness / paralysis of cricothyroid - problems with phonation, particularly at higher pitches
can also cause mild hoarseness and fatiguability to the voice
what does the external laryngeal nerve run in close proximity to?
it is the external branch of the superior laryngeal nerve
supplies cricothyroid muscle
external + internal branches run in close proximity to superior thyroid artery
arterial supply to thyroid?
superior + inferior thyroid arteries
supply of recurrent (inferior) laryngeal nerves?
motor: intrinsic muscles BUT cricothyroid
sensory: subglottic
what do the intrinsic muscles of the larynx control?
entry into the airway (trachea)
vocal cord movement during phonation, coughing, swallowing and breathing
what would unilateral recurrent laryngeal nerve damage result in?
voice change e.g. hoarseness and a weaker cough
why may a patient with unilateral recurrent laryngeal nerve damage present with a weaker cough?
to cough, the vocal cords have to be firmly ADducted, before SNAPPING OPEN to allow expulsion of air from behind
what may happen with time in patients with unilateral recurrent laryngeal nerve damage?
the vocal cord on the opposite side may compensate (by shifting closer towards midline), resulting in v little effect on phonation
why is there not usually significant problems with breathing in unilateral recurrent laryngeal nerve damage?
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
what happens with bilateral recurrent laryngeal nerve damage?
BOTH vocal cords paralysed
speech will be significantly affected (aphonia)
why does aphonia occur with bilateral recurrent laryngeal nerve damage?
vocal cords cannot move
what will the resting position of the vocal cords as a result of bilateral recurrent laryngeal nerve damage lead to? how will patients present?
obstruct movement of air in and out of the trachea
patients present with stridor (high pitched, usually inspiratory) and with significant difficulties with breathing
