2. IX Glossopharyngeal Nerve
CASE HISTORY
Allen is a 43-year-old construction worker. While he was eating dinner, Allen developed
pain in the left side of his throat. The pain was short, brief, and stabbing in nature and only
occurred when he swallowed. Allen was eating fish at the time and assumed that a fish
bone was lodged in his throat. He went to the emergency department and was assessed
by an otolaryngologist, but nothing was found. It was assumed that a fish bone had
scratched Allen’s throat and that his symptoms would soon resolve.
A month later, Allen’s pain was still present; in fact, it had increased. The pain occurred
not only when he swallowed but also when he spoke and coughed. Again, while eating din-
ner, Allen experienced the same pain with swallowing. He got up from the table, but after
a few steps he collapsed unconscious to the floor.
Although Allen quickly regained consciousness, he was immediately taken to the
emergency department where he was put on a heart rate and blood pressure monitor to
evaluate the function of his cardiovascular system. While he was on the monitor, the emer-
gency room physician noticed an interesting correlation. Whenever Allen swallowed, he
had a paroxysm (a sudden recurrence or intensification of symptoms) of pain followed
invariably within 3 to 4 seconds by a decrease in heart rate (bradycardia) and a fall in blood
pressure (hypotension). Allen was examined by a neurologist who noticed no evidence of
reduced perception of pharyngeal pinprick or touch, or of pharyngeal motility. A diagnosis
of glossopharyngeal neuralgia was made. Allen was treated with carbamazepine. His
attacks of pain stopped and his cardiovascular function returned to normal.
ANATOMY OF THE GLOSSOPHARYNGEAL NERVE
The name of the glossopharyngeal nerve indicates its distribution (ie, to the glossus
[tongue] and to the pharynx). Cranial nerve IX emerges from the medulla of the
brain stem as the most rostral of a series of rootlets that emerge between the olive and
the inferior cerebellar peduncle. The nerve leaves the cranial fossa through the jugu-
lar foramen along with cranial nerves X and XI (Figure IX–1). Two ganglia are
situated on the nerve as it traverses the jugular foramen, the superior and inferior
(petrosal) glossopharyngeal ganglia. The superior ganglion is small, has no branches,
and is usually thought of as part of the inferior glossopharyngeal ganglion. The
ganglia are composed of nerve cell bodies of sensory components of the nerve
(Figure IX–2).
164
14. 176 Cranial Nerves
CASE HISTORY GUIDING QUESTIONS
1. What is glossopharyngeal neuralgia?
2. What is the cause of glossopharyngeal neuralgia?
3. What is allodynia?
4. Why did swallowing cause Allen pain?
5. Why did Allen collapse on the floor?
6. Why was carbamazepine used to treat Allen?
7. What is the gag reflex, and why don’t we gag every time a bolus of food passes
through the pharynx?
1. What is glossopharyngeal neuralgia?
Glossopharyngeal neuralgia* is characterized by severe, sharp, lancinating pain in
the region of the tonsil, radiating to the ear. It is similar to trigeminal neuralgia (see
Chapter V) in its timing and its ability to be triggered by various stimuli. For exam-
ple, pain may be initiated by yawning, swallowing, or contact with food in the ton-
silar region. In rare instances, the pain may be associated with syncope (a fall in heart
rate and blood pressure resulting in fainting).
2. What is the cause of glossopharyngeal neuralgia?
Typically, glossopharyngeal neuralgia is idiopathic; that is, no cause can be identi-
fied. Occasionally glossopharyngeal neuralgia is secondary to the compression of
cranial nerve IX by carotid aneurysms, oropharyngeal malignancies, peritonsillar
infections, or lesions at the base of the skull.
3. What is allodynia?
Allodynia is pain that results from a touch stimulus that normally would not cause
pain. The pain is usually burning or lancinating in quality.
4. Why did swallowing cause Allen pain?
Sensory nerve endings in the mucosa of Allen’s pharynx were stimulated by the pas-
sage of a bolus of food and by the movements of the underlying muscles involved
*Some authors use the term vagoglossopharyngeal neuralgia or glossopharyngeal and vagal
neuralgia, instead of glossopharyngeal neuralgia, implying that the pain can radiate into the
distribution of the vagus nerve as well as that of the glossopharyngeal nerve. However, the
original term, glossopharyngeal neuralgia, is recognized by most neurologists and is more
commonly used.
15. Glossopharyngeal Nerve 177
in swallowing, coughing, and speaking. These usually harmless stimuli set off a bar-
rage of pain impulses within the nervous system.
5. Why did Allen collapse on the floor?
Allen collapsed on the floor because his blood pressure dropped so low that he could
not maintain adequate blood flow to his brain. The mechanism for Allen’s fall in
blood pressure and heart rate is not well understood. One hypothesis is that when
the pain is most intense, general sensory impulses from the pharynx stimulate the
nucleus of the tractus solitarius, which, in turn, stimulates vagal nuclei. Impulses
from the parasympathetic component of the vagus nerve act to slow the heart rate
and decrease blood pressure.
Alternatively, the rapidly firing general sensory afferents may, through ephaptic
transmission,* give rise to action potentials in the visceral afferent axons from the
carotid sinus as they travel together in the main trunk of the glossopharyngeal nerve.
The carotid nerve would then falsley report increased blood pressure, causing a
reflexive decrease in heart rate and blood pressure via connections in the brain stem.
6. Why was carbamazepine used to treat Allen?
Carbamazepine is a sodium channel blocking drug that is used to treat a wide range
of conditions from seizures to neuropathic pain. Carbamazepine reduces the neu-
ron’s ability to fire trains of action potentials at high frequency and therefore short-
ens the duration of the paroxysm and frequently abolishes the attacks.
7. What is the gag reflex, and why don’t we gag every time a bolus of food
passes through the pharynx?
The gag is a protective reflex that prevents the entry of foreign objects into the ali-
mentary and respiratory passages. A touch stimulus to the back of the tongue or
pharyngeal walls elicits the gag (see Clinical Testing). Since the passage of a bolus
of food through the pharynx stimulates the tongue and pharyngeal walls, we have
to ask why swallowing does not elicit a gag reflex.
Although the exact mechanism is not well understood, it is generally accepted
that when a swallowing sequence is initiated, probably by signals from the cerebral
cortex to swallowing center(s) in the brain stem, simultaneous inhibitory signals are
sent to the gag center in the brain stem to turn off the gag reflex.
*Ephaptic transmission occurs when a rapidly firing nerve changes the ionic environment of
adjacent nerves sufficiently to give rise to action potentials in them. These “artificial synapses”
often result from a breakdown in myelin.
17. Glossopharyngeal Nerve 179
The sensitivity of the gag reflex can be affected by cortical events. It can be sup-
pressed almost completely or enhanced such that even brushing the teeth or the
sight of a dental impression tray can lead to gagging.
CLINICAL TESTING
Although cranial nerve IX comprises general sensory and motor, visceral sensory and
motor, and special sensory components, from a practical point of view only the gen-
eral sensory component is tested at the bedside. Clinically, cranial nerves IX and X
are assessed by testing the gag reflex. The gag reflex involves both cranial nerves—the
glossopharyngeal being the sensory afferent input and the vagus carrying the motor
efferents. When assessing the gag reflex, right and left sides of the pharynx should be
lightly touched with a tongue depressor (Figure IX–13). The sensory limb of the reflex
is considered to be intact if the pharyngeal wall can be seen to contract after each side
has been touched. (See also Cranial Nerves Examination on CD-ROM.)
Figure IX–13 Testing the gag reflex by lightly touching the wall of the pharynx.
ADDITIONAL RESOURCES
Brodal A. Neurological anatomy in relation to clinical medicine. 3rd ed. New York:
Oxford University Press; 1981. p.460–4, 467.
Ceylan S, Karakus A, Duru S, et al. Glossopharyngeal neuralgia: a study of 6 cases.
Neurosurg Rev 1997;20(3):1996–2000.
Dalessio DJ. Diagnosis and treatment of cranial neuralgias. Med Clin North Am
1991;75(3):605–15.
Dubner R, Sessle BJ, Storey AT. The neural basis of oral and facial function. New York:
Plenum Press; 1978. p. 370–2.
Eyzaguirre C, Abudara V. Carotid body glomus cells; chemical secretion and transmission
(modulation?) across cell-nerve ending junctions. Respir Physiol 1999;115:135–49.
18. 180 Cranial Nerves
Fitzerald MTJ. Neuroanatomy basic and clinical. 3rd ed. Toronto: W.B. Saunders
Company, Ltd.; 1996. p.147–50, 190–1.
Glossopharyngeal neuralgia with cardiac syncope: treatment with a permanent cardiac
pacemaker and carbamazepine. Arch Intern Med 1976;136:843–5.
Haines DE. Fundamental neuroscience. New York: Churchill Livingstone; 1997. p. 261.
Hanaway J, Woolsey TA, Mokhtar MH, Roberts MP Jr. The brain atlas. Bethesda (MD):
Fitzgerald Science Press, Inc.; 1998. p. 180–1, 186–7, 194–5.
Kandel ER, Schwartz JH, Jessel TM. Principles of neuroscience. 3rd ed. New York:
Elsevier Science Inc.; 1996. p. 770–2.
Kiernan JA. Barr’s the human nervous system. 7th ed. New York: Lippincott-Raven; 1998.
p. 169–74.
Kong Y, Heyman A, Entman ML, McIntosh HD. Glossopharyngeal neuralgia associated
with bradycardia, syncope, and seizures. Circulation 1964;30:109–12.
Loewy AD, Spyer KM. Central regulation of autonomic functions. New York: Oxford
University Press; 1990. p. 182–4.
Miller AJ. The neuroscientific principles of swallowing and dysphagia. San Diego: Singular
Publishing Group, Inc.; 1999. p. 100–1.
Moore KL, Dalley AF. Clinically oriented anatomy. 4th ed. New York: Lippincott
Williams & Wilkins; 1999. p. 1104–5.
Nolte J. The human brain. 4th ed. Toronto: Mosby Inc.; 1999. p. 288, 305.
Verna A. The mammalian carotid body: morphological data. In: Gonzalez C, editor. The
carotid body chemoreceptors. Austin (TX): Chapman & Hall, Landes Bioscience;
1997. p. 1–29.
Young CP, Nagaswawi S. Cardiac syncope secondary to glossopharyngeal neuralgia effec-
tively treated with carbamazepine. J Clin Psychiatry 1978;39:776–8.
Young PA, Young JA. Basic clinical neuroanatomy. Philadelphia: Williams & Wilkins;
1997. p. 292, 296.
Zigmond MJ, Bloom FE, Landis SC, et al. Fundamental neuroscience. Toronto: Academic
Press; 1999. p. 1057–60, 1080–4.
![IX Glossopharyngeal Nerve
CASE HISTORY
Allen is a 43-year-old construction worker. While he was eating dinner, Allen developed
pain in the left side of his throat. The pain was short, brief, and stabbing in nature and only
occurred when he swallowed. Allen was eating fish at the time and assumed that a fish
bone was lodged in his throat. He went to the emergency department and was assessed
by an otolaryngologist, but nothing was found. It was assumed that a fish bone had
scratched Allen’s throat and that his symptoms would soon resolve.
A month later, Allen’s pain was still present; in fact, it had increased. The pain occurred
not only when he swallowed but also when he spoke and coughed. Again, while eating din-
ner, Allen experienced the same pain with swallowing. He got up from the table, but after
a few steps he collapsed unconscious to the floor.
Although Allen quickly regained consciousness, he was immediately taken to the
emergency department where he was put on a heart rate and blood pressure monitor to
evaluate the function of his cardiovascular system. While he was on the monitor, the emer-
gency room physician noticed an interesting correlation. Whenever Allen swallowed, he
had a paroxysm (a sudden recurrence or intensification of symptoms) of pain followed
invariably within 3 to 4 seconds by a decrease in heart rate (bradycardia) and a fall in blood
pressure (hypotension). Allen was examined by a neurologist who noticed no evidence of
reduced perception of pharyngeal pinprick or touch, or of pharyngeal motility. A diagnosis
of glossopharyngeal neuralgia was made. Allen was treated with carbamazepine. His
attacks of pain stopped and his cardiovascular function returned to normal.
ANATOMY OF THE GLOSSOPHARYNGEAL NERVE
The name of the glossopharyngeal nerve indicates its distribution (ie, to the glossus
[tongue] and to the pharynx). Cranial nerve IX emerges from the medulla of the
brain stem as the most rostral of a series of rootlets that emerge between the olive and
the inferior cerebellar peduncle. The nerve leaves the cranial fossa through the jugu-
lar foramen along with cranial nerves X and XI (Figure IX–1). Two ganglia are
situated on the nerve as it traverses the jugular foramen, the superior and inferior
(petrosal) glossopharyngeal ganglia. The superior ganglion is small, has no branches,
and is usually thought of as part of the inferior glossopharyngeal ganglion. The
ganglia are composed of nerve cell bodies of sensory components of the nerve
(Figure IX–2).
164](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)