NEUROLOGY
nerve in the medulla. 5 Preganglionic axons travel
in the glossopharyngeal nerve and synapse at the
otic ganglion. 5 The postganglionic axons course
with the auriculotemporal nerve, a branch of the
mandibular nerve, to arrive at the zygomatic and
parotid salivary glands. 5 Preganglionic neurons for
the parasympathetic innervation of the sublingual
and mandibular glands are provided by the
parasympathetic nuclei of the facial nerve in the
medulla. 5 The preganglionic axons course in the
facial nerve, through the tympanic cavity to join the
lingual nerve, a branch of the mandibular nerve, at the
level of the oval foramen. The oval foramen, located
just medial to the temporomandibular joint, is also the
foramen through which the mandibular nerve exits the
cranial cavity. After the preganglionic axons join the
mandibular nerve, they course to the mandibular and
sublingual ganglia and synapse with parasympathetic
ganglionic neurons. Parasympathetic postganglionic
axon coursing with branches of the mandibular nerve
ultimately innervate the mandibular and sublingual
glands. 5
Parasympathetic stimulation of the salivary glands
mediated through acetylcholine is responsible
for salivary production and flow. The sympathetic
nervous system can modulate salivary secretion and
composition through norepinephrine by stimulating
the blood vessels and the acinar cells of the salivary
glands. 6 In general, sympathetic stimulation to the
salivary glands results in vasoconstriction of the blood
vessels, which reduces aqueous saliva and exocytosis
of the acinar glandular cells. Overall, this results in a
more proteinaceous and less voluminous saliva flow. 6
An analysis of Max’s salivation
In patients like Max with dysfunction of the trigeminal
or the mandibular nerve, abnormal saliva that
appears foamy, ropy and stringy accumulates in the
oropharynx on the side ipsilateral to the nerve deficit
(Figure 2). The saliva buildup is located just caudal
to the maxillary fourth premolar, which is where the
openings to the oral cavity are for the parotid gland
and zygomatic gland. 7 .
How can one explain the accumulation of abnormal
saliva?
Given the normal function of cranial nerve VII (ability
to blink the eye) and cranial nerve IX (ability to swallow
normally), the preganglionic parasympathetic axons
to the salivary glands are likely intact. Therefore, the
abnormal composition and flow of saliva produced by
the parotid and zygomatic salivary glands, as evidenced
by accumulation of the thickened saliva in the caudal
oropharynx, is most likely due to dysfunction of the
postganglionic axons that course with the branches
of mandibular nerve.
In cases like Max’s, we hypothesize that the dysfunction
of the trigeminal or mandibular nerve also affects the
postganglionic parasympathetic axons that course
alongside the axons of the trigeminal or mandibular
nerve to reach the salivary glands. In other words,
the loss of the conduit for the postganglionic axon
provided by the trigeminal or mandibular nerve results
in dysfunction of the parasympathetic stimulation
to the salivary glands, which alters salivary flow and
composition.
Normally, the parasympathetic nervous system
is responsible for the production of voluminous
amounts of aqueous saliva. Parasympathetic
denervation results in proteinaceous saliva that is more
viscous than normal. This is appreciated clinically
as an accumulation of thickened, ropy saliva that
accumulates in the oropharynx on the side ipsilateral
to trigeminal or mandibular nerve dysfunction.
The essentiality of salivation, and why it might
go wrong
Figure 2; View of Max's oral cavity reveals the accumulation of
thick, foamy saliva in the left caudal oropharynx.
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Issue 04 | SEPTEMBER 2018 | 22
Normal salivation provides an important role in day-
to-day life. Not only does it aid in food mastication
and digestion but also in lubrication of the oral
cavity, maintenance of normal pH of the mouth, and
prevention of dental caries. 8 Lack of salivation can
cause significant oral discomfort and ulcerations as
well as a detrimental decline in oral health. 9 It’s possible
that with unilateral trigeminal nerve dysfunction
and accumulation of abnormal saliva, there may be
an increase in dental tartar on the side of the nerve
dysfunction. 7