Page 771 - Clinical Small Animal Internal Medicine

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68 The Neurologic Examination 739

For the trigeminal nerve, palpate the muscles of mastica- Grasp the superior jaw with one hand and pull down
VetBooks.ir tion for any denervation atrophy caused by dysfunction of on the inferior jaw with the other hand to open the
mouth. The resistance felt is the result of the function
the mandibular nerve from the trigeminal nerve. The only
evidence of unilateral loss of function of the mandibular
nerve will be unilateral atrophy of the muscles of mastica- of the masticatory muscles that close the mouth and are
innervated by the mandibular nerves from the trigemi-
tion. Be sure to palpate for this atrophy because you will nal nerves. Quickly look at the surface of the tongue for
not see it in breeds with a thick hair coat, such as an old its size and any movement that is present. Push the
English sheepdog. No clinical evidence of any loss of jaw tongue with your finger and observe for any movement.
function will be observed; they can still bite vigorously. This maneuver evaluates the sensory branches of the
A dropped jaw that the patient cannot move requires trigeminal nerves (V) and the motor neurons in the
dysfunction of both mandibular nerves. The observation hypoglossal nerves (XII). Then insert your finger
of a dropped jaw is sometimes aided by holding only the through the oral cavity into the oropharynx and laryn-
superior jaw and associated lips elevated and observing the gopharynx. Feel for the muscle tone and evaluate the
gap created by the inability to elevate the inferior jaw to patient’s sensory response to this maneuver. This
close the mouth. Place the blunt end of your tissue forceps response is the gag reflex. The sensory nerves stimu-
against the nasal septum. The normal patient will immedi- lated include the trigeminal branches to the tongue
ately move its head away from the stimulus. This action surface and oropharyngeal surface of the soft palate
tests two anatomic pathways. One is the integrity of the and both the sensory and motor neurons in the glos-
ipsilateral branch of the ophthalmic nerve from the trigem- sopharyngeal (IX) and vagal (X) nerves. This assessment
inal nerve that innervates the mucosa of the nasal septum. of the gag reflex is difficult to evaluate and is usually
The other is the nociceptive pathway that projects pre- quite subjective. A more reliable indication of dyspha-
dominantly to the opposite side of the rostral brainstem gia usually comes in the form of a complaint by the
and the somesthetic cortex of the opposite cerebral hemi- owner as they watch their animal eating and drinking.
sphere. This evaluation is one of the three clinical examina- These functions can also be assessed by watching the
tions that we routinely use for prosencephalic dysfunction. patient prehend and swallow food.
We do not routinely check the autonomous zones of the I do not routinely test for olfaction or hearing because
other two branches of the trigeminal nerve. they are difficult to evaluate objectively, especially when
they are incomplete. The owner’s observation of their
Cranial Nerves IX, X, and XII animal’s behavior is more reliable for disorders of these
Cranial nerves IX, X, and XII are examined together with functions. Brainstem auditory‐evoked potential (BAER)
the so‐called gag reflex. This examination is performed testing is the most reliable way to evaluate hearing
rapidly because the patient usually objects to the manip- function, especially with unilateral disorders. Tests for
ulation that is necessary, especially cats. olfaction have been described.